Biology Course Notes Unit 1.1. Cells PDF

Biology Course Notes Unit 1.1. | Cells The basic unit of living organisms is the cell. In multicellular animals, cells may be very specialized. The red blood cells (RBC) shown are specialized for oxygen transport. Oxygen binds to the hemoglobin molecules...

Biology Course Notes Unit 1.1. | Cells The basic unit of living organisms is the cell. In multicellular animals, cells may be very specialized. The red blood cells (RBC) shown are specialized for oxygen transport. Oxygen binds to the hemoglobin molecules in the RBCs and is transported throughout the body. One single RBC carries more than 250 million molecules of hemoglobin (https://pixabay.com/illustrations/blood-cells-red-medical-medicine-1813410/) Unit 1.1. Cells Date 01122023 1 Revision | 6 BIOLOGY PROGRAM Welcome to Biology! This is an exciting time to study biology, the science of life. Biologists are continuing to make remarkable new discoveries that affect every aspect of our lives including our health, food, safety, relationships with humans and other organisms and the environment and our planet. New knowledge provides new insights into the human species and the millions of other organisms with which we share the planet and helps us to develop solutions to the complex problems we encounter. In this course we aim to provide you with a strong basis for undertaking further studies in the biological sciences. We will take you on a tour of life and hope to nurture and encourage your interest in this subject. The staff in Biology will work to support you in your studies of Biology as much as possible. The staff are here to help so if you have any questions please do not hesitate to seek assistance from your teachers Best wishes for a successful year. Unit 1.1. Cells Date 01122023 2 Revision | 6 BIOLOGY PROGRAM TABLE OF CONTENTS We will begin our exploration of life through the following topic questions; Chapter Chapter title Page General Information 4 Introduction What is Biology, and how does scientific method work? 7 1 Which molecules are important in living things? 25 2 What are cells and organelles? 56 3 What are biological membranes? 77 4 How do biological reactions work? 96 5 How do living things get their energy? 112 Unit 1.1. Cells Date 01122023 3 Revision | 6 BIOLOGY PROGRAM General Information Biology classes (i) Lectures Each week there is a one 90-minute lecture. Lecture are based on your course notes so you should read through the topic prior to attending the lecture. Attendance at lectures is compulsory. (ii) Tutorial Each week there is a one 90-minute tutorial class. Attendance at tutorial classes is compulsory. Be prepared for tutorial class. Prior to attending class, you should re-read your lecture notes and complete the revision questions for the previous lecture. (iii) Practical classes You will undertake ten (10) practical classes during this course. You will be provided with a timetable for your classes and a practical manual. Details will be provided at your first tutorial class. For Biology practical classes you will require a laboratory coat. Attendance at practical classes is compulsory. You MUST attend a minimum of 80% of practical classes to PASS Biology. Unit 1.1. Cells Date 01122023 4 Revision | 6 BIOLOGY PROGRAM Biology Resources (i) Course Notes For Biology you are provided with course notes. These notes provide the basis for your study of the Biology program. This is the first set of notes for Unit 1.1: Cells. The course notes include the following sections: ICON SECTION TITLE SECTION DESCRIPTION Key Concepts: This lists the main concepts that are covered in the chapter. Learning Outcomes: Provides a list of the outcomes for a chapter. These are the requirements/knowledge you should have developed from your study of this chapter. On completion of your study of the chapter you should return to the learning outcomes to check that you are happy that you can meet the requirement. There is a check box for you to mark. Chapter sections: These contain the information for learning each topic in the Biology course. Bio-in Action: Provides examples of biology in the real world that relate to the chapter of study. These are not examinable. Glossaries: Lists of some key words are provided for you to write in their meaning. You might also add your own words to build this list. Revision questions Completion of the revision questions will assist you to develop an understanding of the topics covered (‘Test Your in the chapter. The questions relate directly to material in the chapter so you should be able to answer Knowledge’): these questions when you have completed your study of the chapter and/or by going back through the notes. They are part of your independent study. ‘On reflection’ pages: These provide an opportunity for you to note some of your own insights, examples, and connections from the topic. Trinity Learning Management System (LMS) It is important that you become familiar with the Biology LMS site. On the Biology LMS site, you will find course notes, worksheets, and answers for revision questions. There is information on exams and access to lecture recordings (Echo360). The Trinity LMS is a useful resource, and it is recommended that you make use of the information provided. If you have any problems accessing our LMS please see your teacher. Unit 1.1. Cells Date 01122023 5 Revision | 6 BIOLOGY PROGRAM Biology Assessment Biology is assessed by exam, assignment and practical class reports. Exam 1 (Semester 1) 30% Exam 2 (Semester 2) 40% Assignment 10% Practical reports 20% Unit 1.1. Cells Date 01122023 6 Revision | 6 BIOLOGY PROGRAM  Introduction – What is Biology, and how does scientific method work? Key Concepts What is Biology? Characteristics of life 1. Cells 2. Growth and development 3. Response to stimuli 4. Reproduction Watson and Crick posed in the early 1990s with a model like the one they made to first describe the structure of DNA. Courtesy Susan Lauter, CSHL. 5. Evolution and adaptation https://www.cshl.edu/letters-shed-new-light-on-nobel-prizes-for-discovery-of-dnas- Life is organised at many levels. double-helix-structure/ Organisation within the organism Organisation between organisms and with the environment. How does scientific method work? Scientific Method– The Practice of Science Observations: “An act or instance of noticing or perceiving” Hypothesis: A possible explanation for an observation is a hypothesis. Scientific Theory: If a hypothesis has been tested positively many, Test: Experimental design many times AND in many different ways it will eventually be referred Data: The results of the experiments are the data. to as a scientific THEORY. Unit 1.1. Cells Date 01122023 7 Revision | 6 BIOLOGY PROGRAM  Learning Outcomes On completion of this topic students should have achieved the following learning outcomes: Level of Section Outcome achievement I.1 Explain what Biology is and provide an example of what could be studied. I.3 Understand that life is defined by a set of characteristics and provide three examples of characteristics of life. I.4 Understand that there are several levels of biological and ecological organisation. I.4 Provide one example of a level of biological organisation within an organism. I.4 Provide one example of ecological organisation. I.5 Describe the steps of observation, hypothesis and experimentation in scientific method. I.5 Given an example, apply the principles of scientific method to design a simple experiment. Unit 1.1. Cells Date 01122023 8 Revision | 6 BIOLOGY PROGRAM  Introduction Chapter Index Section Section title Page I.1 What is Biology? 10 I.2 What does it mean to be ‘alive’? 10 I.3 What are the characteristics of life? 10 I.4 How is life organised? 17 I.5 How does scientific method work? 19 Unit 1.1. Cells Date 01122023 9 Revision | 6 BIOLOGY PROGRAM Section I.1 What is Biology? Biology is the study of living things - the science of life. Living things come in an outstanding variety of shapes and forms and biologists study life in many different ways. Biologists may live with monkeys, collect fossils or listen to whales. They read the messages encoded in the DNA molecules, count how many times ants visit a square metre of ground or find ways to treat disease. Section I.2 What does it mean to be ‘alive’? It is easy to recognise that a tree outside your window, a butterfly flying past or your pet dog are living systems, whereas a rock or a car is not. How do we decide if something is alive or not? When we consider life on Earth, we find that all living things share a common set of characteristics that distinguish them from nonliving things. Section I.3 What are the characteristics of life? 1. Organisms are composed of cells. Even though there is much variation in the size and appearance of living things, all organisms consist of basic units called cells. New cells can only be formed by the division of previously existing cells. Some of the simplest life forms such as protozoa are unicellular organisms meaning that they consist of a single cell. In contrast the body of a human or an elephant or a mouse is composed of billions of cells. These are complex multicellular organisms however made up of the basic unit of organisation, the cell. Unit 1.1. Cells Date 01122023 10 Revision | 6 BIOLOGY PROGRAM  A single celled organism, belonging to Phylum Sarcodina. This is a type of amoeba. Amoeba is a term used to describe cells that can change shape as they move. Figure 1.1 | Phylum Sarcodina includes single celled organisms (https://sites.google.com/site/blakesmsedclassifications/home/about-life/domains- of-living-things/eukarya/protista/sarcodina-amoeboids) Giant kelp forests provide food and shelter for many inhabitants of the oceans. These giant algae are multicellular and photosynthetic and belong to Kingdom Protista. Figure 1.2 | Giant Kelp Forest (NOAA’s National Ocean Service, www.flickr.com/photos/40322276@N04/12801115735) Unit 1.1. Cells Date 01122023 11 Revision | 6 BIOLOGY PROGRAM  2. Organisms grow and develop Biological growth involves an increase in the size of the individual cells, in the number of cells or in both. Growth can be uniform in various parts of an organism or it may be greater in some parts than in others causing the body proportions to change as growth occurs. Some organisms, like trees continue to grow throughout their lives. Other organisms particularly animals have a defined period of growth that ends when the individual has reached adult size. Organisms may develop as well as grow. Development includes all the changes that take place during an organism’s life. Examples of growth and development …. Figure 1.3 | Growth and development in a chicken and in a plant (https://zumeriserly.wordpress.com/2013/09/18/growth-and- development-in-plants-and-animals/) In animals, growth occurs in all parts of the body while in plants growth occurs in specific (meristematic) regions. Plants development is the process toward maturity and can be observed in change in shape and organ function. In animals (including humans) growth and development occurs in two phases – before and after birth. Unit 1.1. Cells Date 01122023 12 Revision | 6 BIOLOGY PROGRAM  3. Organisms respond to stimuli All forms of life respond to stimuli, physical or chemical changes in the internal external environment. Some examples of stimuli that can cause a response include changes in the colour or direction of light, changes in temperature, pressure or sound or changes in the chemical composition of the surroundings including the air or the water. Responding to stimuli involves movement, although not always moving from one place to another. Figure 1.4 | Lemurs sunbathing (image from ‘Wonders of Science’ on Twitter) Figure 1.5 | Little penguin (https://characteristicsoflifebiology.weebly.co m/response-to-stimuli.html) Penguin eyes respond to different environments. The shape of the eye lenses change when the penguin moves form air to water. This allows the penguin to have sharp vision in either environment. Unit 1.1. Cells Date 01122023 13 Revision | 6 BIOLOGY PROGRAM  4. Organisms reproduce At one time people thought worms arose spontaneously from horsehair in a water trough, maggots from decaying meat, and frogs from the mud of rivers. As a result of much scientific work, we now know that organisms arise only from pre-existing organisms. Simple organisms such as a single celled protozoan reproduce by asexual reproduction. When the protozoan has reached a certain size, it reproduces by splitting in half to form 2 new cells. Some plants and animals may also reproduce asexually. In most plants and animals however, reproduction is sexual. Fusion of sperm and egg cells form the fertilised egg, and the new organism develops from this fertilised egg. Figure 1.6 | Pregnant male seahorse (https://theconversation.com/the-secret-sex-life- and-pregnancy-of-a-seahorse-dad-46599) In seahorses, the males (sperm-producers) are the ones that get pregnant. The female transfers her eggs to the male’s pouch and the male releases sperm to fertilise the eggs as they enter. The male carries the offspring for about 3 weeks before they are born. Unit 1.1. Cells Date 01122023 14 Revision | 6 BIOLOGY PROGRAM  Figure 1.7 | Eastern Grey Kangaroo (https://www.livescience.com/14866- kangaroos-mysterious-offspring-swapping-habits.html) Eastern grey kangaroo only produce offspring when the environmental conditions are good to do so. Unit 1.1. Cells Date 01122023 15 Revision | 6 BIOLOGY PROGRAM  5. Populations evolve and become adapted to the environment. Adaptations are inherited characteristics that help an organism to survive in a particular environment. Populations of organisms evolve over many generations and become adapted to their environments. Populations of organisms develop characteristics that allow them to survive in a changing world. The feathers and lightweight bones of birds are adaptations for flying, the thick fur coats of polar bears allow them to survive in freezing temperatures. Every successful biological organism is a complex collection of coordinated adaptations produced through the evolutionary process. Figure 1.8 | Polar bear (https://www.nationalgeographic.org/activity/arctic- adaptations/) Adaptations for flight include lightweight and smooth feathers, streamlined body, wings, hollow bones and enlarged breastbone for attachment of flight muscles. Figure 1.9 | Birds (https://telanganatoday.com/ the-science-behind-birds- flight) Unit 1.1. Cells Date 01122023 16 Revision | 6 BIOLOGY PROGRAM Section I.4 How is life organised? In organisms there are several levels of organisation. Atoms combine chemically to form molecules. Two atoms of hydrogen combine with one atom of oxygen to form a single molecule of water. All life as we know it depends on this simple molecule. At the cellular level different atoms and molecules come together to give rise to cells. The cell forms a basic structural functional unit of life. In multicellular organisms the cells come together to form tissues. Most animals have muscle tissue and nervous tissue for example. Plants have vascular tissues that move materials throughout the plant body. In complex organisms’ tissues come together to form functional structures called organs such as the heart and stomach in animals or the roots and leaves in plants. In animals’ major biological functions are performed by a coordinated group of tissues and organs called an organ system. The circulatory and digestive systems are examples of organ systems. The organs systems function together to make up a complex multicellular organism. There are several levels of ecological organisation. Organisms interact with each other and the environment to form more complex levels of biological organisation. All members of one species living in the same geographic area at the same time make up a population. Populations of different types of organisms that inhabit a particular area and interact with one another form a community. A community can consist of hundreds of different types of organisms. The community together with its nonliving environment is an ecosystem. An ecosystem can be as small as a pond or even a puddle or as huge as one of the deserts of Australia. All of earth's ecosystems together are known as the biosphere. The biosphere includes all systems of earth that are inhabited by living organisms - the atmosphere, the hydrosphere which is water in any form and the lithosphere which is the earth's crust. The study of how organisms relate to each other and their physical environment is ecology. Unit 1.1. Cells Date 01122023 17 Revision | 6 BIOLOGY PROGRAM  Figure 1.10 | Levels of biological organisation (https://www.thinglink.com/scene/58334250642754765 0) Unit 1.1. Cells Date 01122023 18 Revision | 6 BIOLOGY PROGRAM  Section I.5 How does scientific method work? The Practice of Science The scientific method is a way to ask and answer scientific questions by making observations and doing experiments. Biology is a science. Science is a way of thinking and a method of investigating the natural world in a systematic manner. Ideas are tested and based on findings these ideas might be modified or rejected. The scientific method involves a series of ordered steps using the scientific method scientists make careful observations ask critical questions and develop hypothesis. A hypothesis is a simple explanation for an observation. Scientific method has as its basis observation, hypothesis and experiment. Unit 1.1. Cells Date 01122023 19 Revision | 6 BIOLOGY PROGRAM Observation – “An act or instance of noticing or perceiving” An observation can be qualitative (descriptive) or quantitative (based on numbers). In scientific research it may have involved planning and organisation or it may be a chance finding. The observation may lead to questions – Why? How? When? Hypothesis – A possible explanation for an observation is a hypothesis. The hypothesis can be used to make certain predictions, which can be tested by experiments. “If I change this then I expect such and such will happen” Test – Experimental design To test a prediction (a minimum of) two experiments will be undertaken. (i) Test (ii) Control All experiments are affected by many variables. The control is designed so it differs from the test by a single factor. This single factor is the experimental variable that is being tested. Unit 1.1. Cells Date 01122023 20 Revision | 6 BIOLOGY PROGRAM Data - The results of the experiments are the data. Hypothesis supported, if the results of the control and test are different then this may support the hypothesis. Good, do some further testing! Hypothesis not supported, if the results of the control and test are the same then the hypothesis is not supported. It is necessary to reconsider the hypothesis and perhaps make further observations. Whether the hypothesis is supported or not there should be further testing. Experiments and observations must always be repeatable. They must be reported so that another scientist could use the information and carry out the experiments and reach the same conclusions. Scientific Publication - The findings of experimental work are published in scientific journals. Prior to publication the work is subject to review by other scientists in the field. Once published the research findings are available to the scientific community. Scientific theory - If a hypothesis has been tested positively many, many times AND in many different ways it will eventually be referred to as a scientific THEORY. Examples: Cell theory – all living things are composed of cells. Evolutionary theory – all organisms have a common ancestor and are adapted to their environment. Gene theory – inherited information (DNA) controls the form and function of an organism. Unit 1.1. Cells Date 01122023 21 Revision | 6 BIOLOGY PROGRAM  Glossary for Cells Introduction. Write the definitions for these words yourself. Add any extra words that are helpful for you! Cell: Growth: Development: Stimulus: Ecology: Observation: Hypothesis: Unit 1.1. Cells Date 01122023 22 Revision | 6 BIOLOGY PROGRAM  ON REFLECTION, A BIGGER PICTURE: Some ways these topics connect into the wider world, some points that caught my interest… Unit 1.1. Cells Date 01122023 23 Revision | 6 BIOLOGY PROGRAM  Test your knowledge 1 What is Biology? If you were a biologist what would you like to study? 2 An insect is a living thing while a rock is not. Describe three characteristics of life observed in an insect but not a rock. 3 The broadest category of biological organisation is the biosphere. What is the biosphere? 4 Other than the biosphere, describe one example of a level of ecological organisation. Describe one example of a level of organisation within an organism. 5 Scientific method is based on observation, hypothesis and experiment. Briefly describe each of these steps. Congratulations! You have completed the introduction to BIOLOGY. Which of the learning outcomes have you achieved? Check them off on your learning outcomes checklist at the start of this chapter. Unit 1.1. Cells Date 01122023 24 Revision | 6 BIOLOGY PROGRAM Chapter 1 | Which molecules are important in living things? Key Concepts Water: Properties & importance to life. DNA molecules are double stranded and form a helical structure. https://www.britannica.com/science/genetics/DNA-and-the-genetic-code Carbohydrates: monosaccharides, disaccharides and polysaccharides Lipids: Neutral fats, phospholipids and steroid Proteins: Amino acids, peptides, organization, fibrous compared to globular proteins. Nucleic Acids: Nucleotides, DNA compared to RNA. Unit 1.1. Cells Date 01122023 25 Revision | 6 BIOLOGY PROGRAM  Learning Outcomes On completion of this topic students should have achieved the following learning outcomes: Level of Section Outcome achievement 1.1 Identify hydrogen bonds as being responsible for the special properties of water. 1.1 Name and describe one property of water. Explain how this property is important for living things. Explain the terms; monosaccharide, disaccharide and polysaccharide with reference to carbohydrates. Name the bond 1.2 that links monosaccharide units to form disaccharides or polysaccharides. Name and provide an example of a storage and a structural polysaccharide in animals and in plants. Identify a triglyceride, a phospholipid and a steroid molecule. With respect to triglycerides identify the fatty acid chains. 1.3 Describe the difference between a saturated and an unsaturated fatty acid. Provide examples of the function of triglycerides, phospholipids and steroids. Explain the characteristics of phospholipids that result in bilayer formation. Understand that proteins are composed of amino acids. Draw and label a diagram of the general structure of amino 1.4 acids and identify the peptide bond as the bond that links amino acids. Define the primary, secondary, tertiary and quaternary structures of a protein. Identify the bond types that are important 1.4 in maintaining each of these levels of structure. Explain the effect of changes in temperature and pH on the structure of a protein 1.5 Describe the function of DNA and RNA and the components of a nucleotide. Name the link that forms between nucleotides to form a nucleic acid. 1.5 List three structural differences between DNA and RNA. Unit 1.1. Cells Date 01122023 26 Revision | 6 BIOLOGY PROGRAM  Chapter 1 Index Section Section title Page 1.1 Water 28 1.2 Carbohydrates 31 1.3 Lipids 34 1.4 Proteins 39 1.5 Nucleic acids 48 Unit 1.1. Cells Date 01122023 27 Revision | 6 BIOLOGY PROGRAM Section 1.1 Water Water is the most abundant molecule found in living things Properties (physical and chemical) of water make it ideal for sustaining life. For example, each of the following properties: solvency, high heat of vaporisation, cohesion and adhesion, varying density). The properties arise due to hydrogen bonding. Hydrogen bonds form due to weak charge interactions. In a water molecule, the oxygen (O) atom has a weak negative charge while the hydrogen (H) atoms have a weak positive charge. As a result, a weak attraction (hydrogen bond) can form between water molecules. As Figure 1.1 shows a single water molecule can form a maximum of four hydrogen bonds. Hydrogen bonds also can occur in and between other types of molecules and are important in many biological molecules Figure 1.1 | Hydrogen bonding occurs between water molecules (Knox et al., 2005) Unit 1.1. Cells Date 01122023 28 Revision | 6 BIOLOGY PROGRAM How do the properties of water benefit living things? Cohesion: When water molecules stick Adhesion: When water molecules stick to Water is a universal solvent: Water can together due to their hydrogen bonds. This other molecule due to their hydrogen bonds surround the charged molecules of other can be seen when droplets are form on a This can be seen as wicking or substances. The molecules in the substance surface. absorbing/drawing off liquid by capillary are separated by the water molecules and action. the substance dissolves. The cohesion and adhesion properties of This allows molecules to be dissolved in the water allow the upward movement of water blood and other body fluids for transport. and dissolved minerals in plants. https://phys.org/news/2019-10-impact-droplets- https://www.discovercarpetcare.com/2017/07/01/carp https://www.saddlespace.org/whittakerm/ quickly-triggers-stress.html et-stains-come-back-carpet-cleaning/paper-towel- science/cms_page/view/7795247 capillary-action/ Unit 1.1. Cells Date 01122023 29 Revision | 6 BIOLOGY PROGRAM More properties of water ……. High specific heat capacity: Water can Different state densities: Ice (water in solid High heat of vaporisation: It takes a lot of absorb a lot of heat before it gets hot. This form) is less dense than liquid water. This energy to transform liquid water in water helps living things maintain a constant means ice can float in liquid water. vapor (gas). When this happens, heat is temperature even when heat is produced by A layer of ice over a body of water has an removed from a surface and the surface is biochemical reactions. insulating effect. Water under the ice layer cooled. The cooling effect can help protect does not freeze so aquatic life can survive. organisms from overheating. https://www.gettyimages.com.au/detail/photo/t https://wonderopolis.org/wonder/why-does-ice-float- https://www.dreamstime.com/illustration/wiping- hermal-image-of-young-male-athlete-training- in-water sweat.html with-royalty-free-image/499135717 Unit 1.1. Cells Date 01122023 30 Revision | 6 BIOLOGY PROGRAM Section 1.2 Carbohydrates Carbohydrates are the most abundant organic compounds in living things. The general formula for a carbohydrate is Cn(H2O)n. The basic unit for all carbohydrates is the sugar molecule (monosaccharide). Monosaccharides polymerise (link together) to form disaccharides or polysaccharides. Fig 1.2 |Glucose (monosaccharide) and sucrose (disaccharide) (Knox et al., 2005) Monosaccharides Disaccharides Simple sugars are composed of a single sugar molecule Two monosaccharides joined by a glycosidic bond form a disaccharide. and are sweet tasting. Examples of disaccharides found in living things include: The most abundant monosaccharide is glucose (Figure 1.2). (i) Sucrose (glucose & fructose) form in which plants transport sugar. It is the primary product of photosynthesis and primary (ii) (ii) Lactose (glucose & galactose) form of sugar that mammals energy source for most living things. produce in their milk. Unit 1.1. Cells Date 01122023 31 Revision | 6 BIOLOGY PROGRAM Polysaccharides Many monosaccharides joined by glycosidic bonds form polysaccharides. Polysaccharides have many functions in living things. Examples include: (i) Storage polysaccharides Starch: storage polysaccharide of higher plants Glycogen: Storage polysaccharide in animals. Figure 1.3 | Starch (Knox et al., 2005) Unit 1.1. Cells Date 01122023 32 Revision | 6 BIOLOGY PROGRAM (ii) Structural polysaccharides Cellulose: Cell walls of plants Chitin: Structural material found in the exoskeletons of insects and crustaceans. Figure 1.4 | Cellulose (Knox et al., 2005) Unit 1.1. Cells Date 01122023 33 Revision | 6 BIOLOGY PROGRAM Section 1.3 Lipids Lipids are oily, greasy or waxy substances extracted from biological materials. Lipids have a number of important roles in biological systems including: i. energy storage ii. insulation iii. structural component of biological membranes iv. chemical messengers. There are three main groups of lipids. Triglycerides (Fats and Oils) Fats and oils allow an efficient storage of chemical energy. On average, fats and oils yield 2 to 3 times more energy per gram than carbohydrates or proteins. Fats provide insulation – protection from external cold e.g., whales. Figure 1.5 | A fat or oil is composed of a glycerol (grey) and three fatty acids (yellow). It is a triglyceride. (Campbell & Reece, 2002) Unit 1.1. Cells Date 01122023 34 Revision | 6 BIOLOGY PROGRAM Saturated and unsaturated fats Fatty acid chains may be saturated or unsaturated. Saturated fatty acids contain a maximum number of hydrogen atoms attached to the carbon atoms. The fatty acid chains shown in Figure 1.5 are all saturated. Unsaturated fatty acids contain one or more carbon - carbon double bonds (C=C). Monounsaturated fatty acids contain a single C=C while a polyunsaturated fatty acids contain more than one C=C. Figure 1.6 | Fatty Acid chains may be saturated or unsaturated (http://acebiochemistry.yolasite.com) Unit 1.1. Cells Date 01122023 35 Revision | 6 BIOLOGY PROGRAM Phospholipids Phospholipids are the main structural component of biological membranes. Structurally they are similar to triglycerides except have 2 FA chains, and one phosphate group attached to glycerol. Figure 1.8b | Phospholipid molecules on water. The hydrophilic head (phosphate group) comes into contact with the water, the hydrophobic tail (fatty acid chains) point away from the water (Knox et al., 2005) Figure 1.8a | Phospholipid (Knox et al., 2005) Unit 1.1. Cells Date 01122023 36 Revision | 6 BIOLOGY PROGRAM Cell membranes and phospholipid bilayers The phosphate group is hydrophilic (loves water) and soluble in water whereas the fatty acid is hydrophobic (hates water) and insoluble. Molecules that have both hydrophobic and hydrophilic regions are amphipathic. These properties mean that in water, phospholipids can form a bilayer. The phospholipid bilayer is the main component of cell membranes. Figure 1.8 c | Phospholipid molecules on water. The hydrophilic head (phosphate group) comes into contact with the water, the hydrophobic tail (fatty acid chains) point away from the water (Knox et al., 2005) Unit 1.1. Cells Date 01122023 37 Revision | 6 BIOLOGY PROGRAM Steroids Steroids are structurally very different to other lipids. The structure is based on four carbon rings which are derived from cholesterol. Many steroids are hormones, for example, testosterone, oestrogen, progesterone. Figure 1.9 | The structure of cholesterol and testosterone (Mader, 2010) Unit 1.1. Cells Date 01122023 38 Revision | 6 BIOLOGY PROGRAM Section 1.4 Proteins Proteins perform a huge range of functions. For example, proteins act as enzymes for metabolism; involved in structure, movement, nutrition, storage and transport; antibodies and toxins for defence and attack; hormones The building blocks of proteins are amino acids (aa). There are 20 common amino acids. (The structures for all 20 are provided on the LMS). All amino acids have the same basic structure. The R- group is variable. YOU MUST BE ABLE TO DRAW THE GENERAL STRUCTURE OF AN AMINO ACID. Figure1.10a | Generalised structure of an amino acid (Mader, 2010) Unit 1.1. Cells Date 01122023 39 Revision | 6 BIOLOGY PROGRAM Examples of common amino acids Examples of four common amino acids are provided. Note: the basic structure is the same while the R (or variable group) differs. The amino acids show different properties because of these differing R groups. If the R group is nonpolar then the amino acid is hydrophobic whereas if the R group is polar/ionized/charged, then it is hydrophilic group. Figure1.10b | Examples of four common amino acids are provided (Mader, 2010) (polar) Unit 1.1. Cells Date 01122023 40 Revision | 6 BIOLOGY PROGRAM A protein is a chain of amino acids linked by peptide bonds. The following terms apply to amino acids linked by peptide bonds: (i) Peptide – two or more amino acids linked by peptide bonds. (ii) Polypeptide – a chain of more than 10 amino acids linked by peptide bonds. (iii) Protein – protein molecules consist of one or more long chains of amino acids (polypeptides) linked by peptide bonds. Figure 1.11 | Formation of a dipeptide (Knox et al., 2005) Unit 1.1. Cells Date 01122023 41 Revision | 6 BIOLOGY PROGRAM Structure and conformation of proteins Proteins have four levels of organisation (i) Primary structure The primary structure is the sequence of amino acids for a particular protein. The amino acids are linked by peptide bonds. Figure 1.12 Primary structure of the hormone insulin (Knox et al., 2005). Unit 1.1. Cells Date 01122023 42 Revision | 6 BIOLOGY PROGRAM  (ii) Secondary structure The chain of amino acids may undergo coiling (to form an a -helix) or pleating (to form a b-sheet) which is the secondary structure. This structure is held together by hydrogen bonds. These extend between H (slightly positive) to an O (slightly negative) atoms. Figure1.13 | Secondary structure (Knox et al., 2005) Unit 1.1. Cells Date 01122023 43 Revision | 6 BIOLOGY PROGRAM  (iii) Tertiary structure The tertiary structure is the overall three-dimensional (3D) shape of a protein that results from folding and twisting of the secondary structure. Figure 1.14 | Tertiary structure of Myoglobin, an oxygen carrying protein from muscle (Knox et al., 2005) Unit 1.1. Cells Date 01122023 44 Revision | 6 BIOLOGY PROGRAM Figure 1.15 | The tertiary structure is held by a number of different types of R group interactions with each other or surrounding water. These include hydrogen bonds, ionic bonds, covalent bonds, and hydrophobic interactions (Campbell et al., 2006). Unit 1.1. Cells Date 01122023 45 Revision | 6 BIOLOGY PROGRAM  (iv) Quaternary structure The quaternary structure describes the arrangement of the amino acid chains relative to one another and only applies if the protein is composed of more than one chain of amino acids. (Many proteins do NOT have a quaternary structure). Figure 1.16 | Quaternary structure. (a) Collagen is a fibrous protein with an elongated structure while (b) haemoglobin is an example of a globular protein with tightly folded chains (Campbell & Reece, 2002) Unit 1.1. Cells Date 01122023 46 Revision | 6 BIOLOGY PROGRAM The importance of protein shape For the protein to carry out its function, it is the overall shape of the protein that is important. The protein shape will be disrupted if any of the bonds holding it together are broken. If this occurs the protein is denatured and it will no longer function. Figure 1.17 | Modifying pH or temperature can have the effect of denaturing a protein (https://ib.bioninja.com.au/standard-level/topic-2- molecular-biology/24-proteins/denaturation.html) Unit 1.1. Cells Date 01122023 47 Revision | 6 BIOLOGY PROGRAM Section 1.5 Nucleic acids Nucleic acids transmit hereditary information and determine which proteins a cell makes. Nucleic acids are found in all cells and viruses. There are two types of nucleic acid - deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). The nucleic acids are chains of nucleotides units. The structure for a nucleotide includes a 5-carbon sugar, phosphate group and nitrogenous base. Figure 1.18 | Nucleotide structure (https://biologydictionary.net/nucleotide) Unit 1.1. Cells Date 01122023 48 Revision | 6 BIOLOGY PROGRAM Structural differences between DNA and RNA DNA RNA Sugar is deoxyribose Sugar is ribose Adenine, guanine, cytosine and thymine Adenine, guanine, cytosine and uracil Double stranded, double helix in which adenine pairs with Usually single stranded thymine while guanine pairs with cytosine DNA stores genetic information. Each DNA molecule is made up of many genes. The genes carry the code for making proteins. RNA is associated with protein synthesis. Unit 1.1. Cells Date 01122023 49 Revision | 6 BIOLOGY PROGRAM Nucleic acids are chains of repeating nucleotide units. Nucleotides link to one another through phosphodiester bonds to form a nucleic acid. Figure 1.17 | Nucleotides link to each other to form a nucleic acid. RNA is shown. (http://humanbiologylab.pbworks.com/w/page/44855656 /RNA) Unit 1.1. Cells Date 01122023 50 Revision | 6 BIOLOGY PROGRAM  “One drop of lemon juice in a cup of water?” “One drop of lemon juice in a cup of water?” Could you imagine just one drop of lemon juice in a cup of water being enough to kill a person? Ok, well it’s not literally one drop of lemon juice in a cup of water. You should have lemons and oranges – they’re good for you! The equivalent pH change of adding one drop of lemon juice to a cup of water; if that pH change happened in our blood, we could not survive. pH is really important to living things, because it affects our proteins. Anything that messes up a proteins shape messes up its function. pH is one of those things that messes up protein shape. We have a lot of proteins in our blood so CO2 exits our body, helping our blood pH come back to normal. keeping them the right shape is really important. Urinating also helps blood pH get back to normal. Our kidneys can remove Our normal blood pH is approximately 7.3-7.4, depending extra H’s and actively secrete them out of our blood into our urine so they can’t on if it’s in an artery or a vein. If pH gets below 6.8 or hurt our body. above 7.8, it will kill us. One thing that makes blood more acidic is CO2: a product of aerobic respiration. This is So, breathing and urinating, are both very good things for our health, and part because when CO2 travels in blood it does this as a of this is because they help maintain body homeostasis by keeping it a nice dissolved acid. When we breathe out, the place for our proteins to be. Unit 1.1. Cells Date 01122023 51 Revision | 6 BIOLOGY PROGRAM  Glossary for Cells chapter 1. Write the definitions for these words yourself. Add any extra words that are helpful for you! Protein: Carbohydrate: Steroid: Disaccharide:.. Lipid:.. Monosaccharide:.. Nucleic acid: Phospholipid: Polysaccharide: Unit 1.1. Cells Date 01122023 52 Revision | 6 BIOLOGY PROGRAM  ON REFLECTION, A BIGGER PICTURE: Some ways these topics connect into the wider world or with other topics, some points that caught my interest… Unit 1.1. Cells Date 01122023 53 Revision | 6 BIOLOGY PROGRAM  Test your knowledge 1 Provide one example of a property of water. Describe this property and how it is useful to living things. 2 a. What is a monosaccharide? Provide an example. b. What is a disaccharide? Provide an example. c. What is a polysaccharide? Name two polysaccharides and give an example of their function in living things 3 a. Give an example of a function of a triglyceride in a human. b. Triglycerides are composed of a glycerol and three fatty acids. What is the difference between a saturated and unsaturated fatty acid? 4 Draw the structural formula of a simple amino acid, and identify the carboxyl group, amino group and the R-group. How many common amino acids are there? a. Draw an example of a non-polar amino acid. Label amino, carboxyl and R groups. Would you expect the R group to be hydrophobic or hydrophilic? b. Draw an example of a charged amino acid. Label amino, carboxyl and R groups. Would you expect the R group to be hydrophobic or hydrophilic? 5 Refer to Figure 1.14 (tertiary structure of myoglobin) to answer the following. a. In the protein myoglobin, the secondary structure is mainly __________________. b. he tertiary structure of this protein is globular. What type of interactions hold the protein in this shape? c. Does this protein have a primary structure? Explain 6 a. Name the three components of a nucleotide. b. Describe two structural differences between RNA and DNA. Unit 1.1. Cells Date 01122023 54 Revision | 6 BIOLOGY PROGRAM  Well done! Another chapter completed! Now go back to the learning outcomes at the start of this chapter. What have you learnt? What might you need to revise? Unit 1.1. Cells Date 01122023 55 Revision | 6 BIOLOGY PROGRAM Chapter 2 | What are cells and organelles? Key Concepts Cell theory Features of cells - What are cells? What are their sizes? Prokaryotic cells - No nucleus. Eukaryotic cells – Have a membrane bound nucleus and membrane bound organelles. Organelles and the internal structure of cells - The membrane bound organelles of a eukaryote include nucleus; lysosomes; vacuole, mitochondria; chloroplasts. Other structures found in the Purkinje Neurons are involved in motor coordination. These are some the largest neurons in the body and are found as part of the human nervous system. These are eukaryotic cell include the cytoskeleton; centrosome (centriole); examples of eukaryotic cells. flagella and cilia. http://www.kidneynotes.com/2013/07/currentsinbiology-cerebellar-purkinje.html. Unit 1.1. Cells Date 01122023 56 Revision | 6 BIOLOGY PROGRAM  Learning Outcomes On completion of this topic students should have achieved the following learning outcomes: Level of Section Outcome achievement 2.1 Describe the three components of cell theory. Identify five features common to all cells and demonstrate a basic understanding of differences in the size and 2.2 complexity of cells. 2.3 Draw and label a simple diagram of a prokaryotic cell and its structures. 2.3 - 2.4 Define prokaryotic and eukaryotic with regards to cell types and distinguish between the two cell types. 2.5 Describe the advantages to eukaryotic cells of having membrane-bound organelles. Describe the function of each of the following organelles and structures in eukaryotic cells: Cell membrane, cytosol, nucleus, rough endoplasmic reticulum (RER), smooth endoplasmic reticulum (SER), vesicles, Golgi apparatus, 2.5 lysosomes, vacuoles, mitochondria, chloroplasts, cytoskeleton, centrosome (MTOC) and centrioles, flagella and cilia. Recognise the appearance of and identify each of the above organelles and structures on a diagram of a cell. 2.5 Identify the components of a mitochondrion, including outer and inner membrane, intermembrane space, matrix and proteins of the electron transport chain (ETC) and label each in a simple diagram. 2.5 Identify the components of a chloroplast, including outer and inner membranes, thylakoid membranes, grana and stroma and label each of them in a simple diagram 2.5 Distinguish between a plant and animal cell by identifying or describing 2-3 structures unique to each of these two cell types. Unit 1.1. Cells Date 01122023 57 Revision | 6 BIOLOGY PROGRAM  Chapter 2 Index Section Section title Page 2.1 Cell theory 59 2.2 Features of cells 59 2.3 Prokaryotes (no nucleus) 61 2.4 Eukaryotes (membrane bound nucleus) 62 2.5 Organelles & Structures 63 Unit 1.1. Cells Date 01122023 58 Revision | 6 BIOLOGY PROGRAM Section 2.1 | Cell theory All living organisms are made up of one or more cells, and materials produced by cells. Cells are the basic unit of organisation of all organisms. All cells come from pre-existing cells. Section 2.2 | Features of cells Cells are small membrane bound structures in which biological reactions occur. All cells have the following features: Some structure separating the inside from the outside (membrane) Semifluid substance (cytosol) DNA, genetic information for the cell RNA, for protein synthesis Ribosome - structures that respond to the DNA (via the RNA) to produce proteins Unit 1.1. Cells Date 01122023 59 Revision | 6 BIOLOGY PROGRAM Cell size Cells vary enormously in their size and complexity. Most cells are microscopically small. Figure 2.1 | Cell size (Campbell & Reece, 2002) Unit 1.1. Cells Date 01122023 60 Revision | 6 BIOLOGY PROGRAM Section 2.3 | Prokaryotes (no nucleus) Organisms from the domains Bacteria and Archaea are prokaryotes. Prokaryotic cells have NO membrane bound nucleus. The bacterial DNA is present as a single, circular chromosome and is found in the cytosol. This prokaryotic cell in the image is complex. Many prokaryotic cells have only cell membrane, cytosol, DNA (and RNA) and ribosomes. They have no other structures. Figure 2.2 | A prokaryotic cell (Campbell & Reece, 2002) Unit 1.1. Cells Date 01122023 61 Revision | 6 BIOLOGY PROGRAM Section 2.4 | Eukaryotes (membrane bound nucleus) Eukaryotic cells have an internal membrane bound nucleus. All living things, other than prokaryotes, are composed of eukaryotic cells. Eukaryotic cells possess internal membrane bound compartments called organelles ‘little organs’. Some of the organelles include the nucleus, endoplasmic reticulum (ER) - smooth & rough, Golgi complex, mitochondria, chloroplast, vacuoles, lysosomes, flagella and cilia. Figure 2.3 | Eukaryotic (animal) cell (Mader, 2010) Unit 1.1. Cells Date 01122023 62 Revision | 6 BIOLOGY PROGRAM Section 2.5 | Organelles & Structures There are a number of advantages for cells having membrane bound compartments. Membrane results in a closed space so certain activities are localised in a small region of the cell. Specific molecules are localised in one area and are more likely to come into contact, which increases the rate of reaction. Certain molecules (such as enzymes in lysosomes) could potentially damage parts of the cell. The membrane enclosed space keeps such molecules away from other parts of the cell. Membranes allow the cell to store energy. The membrane may provide a barrier that is analogous to a dam. A difference in the concentration of a substance on two sides of the membrane is a form of potential energy which when required by the cell can be converted into chemical energy. Cell organelles & structures Nucleus contains most of the cell’s DNA controls the activities of the cell Structure The nucleus is surrounded by a double membrane called the nuclear envelope. Holes in the nuclear envelope are called nuclear pores. They allow movement of certain molecules into and out of the nucleus. The nucleolus is a dark staining region inside the nucleus and is the site of synthesis of ribosomal RNA. The chromosomes are found in the nucleus. They are composed of a complex of DNA and proteins (chromatin) and become visible when the cell divides. Unit 1.1. Cells Date 01122023 63 Revision | 6 BIOLOGY PROGRAM  Ribosomes Site of protein synthesis Found in all cell types Structure Ribosomes are small granular structures, 25- 30nm in diameter. Typically, the cytosol contains several million ribosomes. In eukaryotic cells, ribosomes may be associated with the Rough Endoplasmic Reticulum. Figure 2.4 | Nuclear envelope and membranes of the endoplasmic reticulum (ER). (https://www.britannica.com/science/ endoplasmic-reticulum) Unit 1.1. Cells Date 01122023 64 Revision | 6 BIOLOGY PROGRAM Endoplasmic Reticulum (ER) A continuous membrane system dedicated to protein synthesis modification and transport Structure The Endoplasmic reticulum is an extension of the outer membrane of the nuclear envelope. This membrane network extends throughout the cytosol. The folds in the membrane network are called cisternae, and the internal space is the lumen. Rough ER Proteins (synthesised by the ribosomes) move inside the rough ER for folding into 3D shape and further processing. Structure Ribosomes are attached to the outside surface give the rough ER a rough appearance. Smooth ER No ribosomes Site of lipid metabolism (that is, synthesis and breakdown of lipids) Breakdown, and so, detoxify lipid soluble drugs and harmful metabolic products. Some types of cells have large amounts of SER, for example, liver cells which are responsible for breakdown of various toxins. Structure Smooth, tubular appearance Unit 1.1. Cells Date 01122023 65 Revision | 6 BIOLOGY PROGRAM  Golgi apparatus Delivery system of the cell. Molecules (from ER and carried in a vesicle) enter the Golgi apparatus on the cis face and are modified, sorted and packaged in vesicles, which deliver the molecules to specific destinations. Vesicles leave the Golgi apparatus at the trans face Structure Stacks of 3-10 slightly curved flattened sacs. Number of stacks varies depending on the type of cell. Vesicles Transport molecules within the cell Structure Small membranous sac Figure 2.5 | Vesicles carrying materials to and away from the Golgi Apparatus (shown in pink) (https://cnx.org/contents/[email protected]:fV7KwqTE@5/The-Cytoplasm-and-Cellular-Org) Unit 1.1. Cells Date 01122023 66 Revision | 6 BIOLOGY PROGRAM Lysosomes Membrane bound organelles found in animal cells that breakdown many types of unwanted materials using enzymes. Examples of uses: Allows the cell to breakdown worn out organelles. An immune system cell may ingest a bacterium. Lysosomes are used to breakdown the bacterium inside the cell. Examples of diseases due to lysosome problems: Tay Sachs disease: normal lipids fail to break down in brain cells due to one lysosome enzyme being absent. The lipid accumulates, damaging cells and causing death. Vacuoles Vacuoles are membranous sacs (but larger than vesicles). In plant cells vacuoles tend to be large and prominent. Vacuoles are not usually found in animal cells. One exception is the cells of adipose (fat) tissue which contain vacuoles that store lipids. As much as 90% of a plant cell may be occupied by the vacuole containing water, stored food, salts, pigments and wastes. Unit 1.1. Cells Date 01122023 67 Revision | 6 BIOLOGY PROGRAM Mitochondria Mitochondria have their own DNA, make some of their own proteins and are able to grow and divide. Cellular (aerobic) respiration occurs. (Cellular respiration is the release of energy from sugars and fats. The released energy is used to produce ATP, which drives other reactions in the cell). Structure Mitochondria are surrounded by a double membrane. The outer membrane is highly permeable (allowing ions and small molecules to pass through readily); while the inner membrane is highly impermeable and has many folds (cristae). Enzyme complexes on the inner membrane are involved in cellular respiration. The core of the mitochondria is the matrix space (contains DNA and ribosomes). Figure 2.6 | Mitochondrion (Knox et al., 2005) Unit 1.1. Cells Date 01122023 68 Revision | 6 BIOLOGY PROGRAM Chloroplasts Chloroplasts have their own DNA, make some of their own proteins and are able to grow and divide. Site of photosynthesis (convert light energy into chemical energy). Found in plant and algae cells. Numbers in a cell vary (unicellular algae may have one whereas a plant leaf cell may have 20-100). Structure Chloroplasts have a double outer membrane. The inner membrane encloses a fluid filled space called the stroma. They contain a third internal system of membranes. These are the thylakoid membranes. The thylakoid membranes extend throughout the stroma and are arranged in stacks called grana (granum). Figure 2.7 | Chloroplast (Knox et al., 2005) Unit 1.1. Cells Date 01122023 69 Revision | 6 BIOLOGY PROGRAM Cytoskeleton All eukaryotes contain a cytoskeleton. Cytoskeleton is a crisscrossed network of protein fibres. Functions include: Supporting the shape of the cell; Anchoring organelles to fixed locations Acting as a frame work on which organelles may be moved around the cell Fibres of the cytoskeleton are dynamic, that is, constantly being assembled and disassembled. There are 3 different types of fibres - microfilaments, intermediate filaments and microtubules. The cytoskeleton is composed of microfilaments, intermediate filaments and microtubules (actin filaments). These fibres are each made of protein units Figure 2.8 | Cytoskeleton (Knox et al., 2005) Unit 1.1. Cells Date 01122023 70 Revision | 6 BIOLOGY PROGRAM Microtubules Microtubules are hollow cylinders that are the components of the cytoskeleton. They have a number of functions in the cell. Microtubules are part of the cytoskeleton, found in flagella and cilia, and help during cell division. Microtubule assembly is controlled by the microtubule organising centre, MTOC (which is also referred to as the centrosome in some cells). The MTOC usually lies near the nucleus and microtubules extend out from it. Microtubule is composed of pairs of tubulin units. The addition of tubulin units makes the structure longer. Whilst removal shortens the structure Figure 2.9 | Microtubule structure (Mader, 2010) Unit 1.1. Cells Date 01122023 71 Revision | 6 BIOLOGY PROGRAM Centrioles Associated with the centrosome. Centrioles are found in animal cells ONLY. The function of centrioles is uncertain (although they may have a role in the cell division process). In plant and most fungal cells centrioles are absent. Flagella and Cilia Structures that allow movement of a cell, or to move substances across the surface of the cell. Flagella tend to be long in proportion to the size of the cell, and cell usually only has one (or two). Cilia are short and generally a cell has many. Structure Cilia and flagella are covered by the cell membrane and contain cytosol. Inside they consist of a circle of nine microtubule pairs surrounding two central ones - 9+2 structure (axoneme) Movement results from sliding of microtubule Figure 2.10 | A cross section of a flagellum showing the internal 9+2 doublets adjacent to each other. arrangement of microtubules (Knox et al., 2005) Unit 1.1. Cells Date 01122023 72 Revision | 6 BIOLOGY PROGRAM  Mitochondrial Disease Did you know that mitochondria are responsible for providing more than 90% of the energy that your body needs to sustain life and support normal organ function? If mitochondria are dysfunctional, it can lead to mitochondrial disease. Cells are not able to generate enough energy to sustain a normal quality of life. Cell injury and cell death can follow. If this process is repeated throughout the body, whole organ systems can start to fail. Mitochondrial disease can be caused by exposure to certain medicines or toxic substances that inhibit the function of electron transport chain, but most of the time, is an inherited genetic condition. A wide range of symptoms may appear in an affected individual, and this can make an accurate diagnosis somewhat difficult! Unit 1.1. Cells Date 01122023 73 Revision | 6 BIOLOGY PROGRAM  Lysosome: Glossary for Cells chapter 2. Write the definitions for these words yourself. Add any extra words that are helpful for you! Mitochondria: Centriole: Nucleus: Centrosome: Nucleolus: Chloroplast: Organelle: Cilia: Prokaryote: Cytoskeleton: Ribosome: Endoplasmic reticulum: Vacuole: Eukaryote: Vesicle: Flagella: Unit 1.1. Cells Date 01122023 74 Revision | 6 BIOLOGY PROGRAM  ON REFLECTION, A BIGGER PICTURE: Some ways these topics connect into the wider world or with other topics, some points that caught my interest… Unit 1.1. Cells Date 01122023 75 Revision | 6 BIOLOGY PROGRAM  Test your knowledge 1 Eukaryotic cells have membrane bound organelles. What are the advantages of having internal membrane bound compartments? 2 Draw a prokaryotic cell and label its components. 3 Some liver cells contain a large amount of Smooth Endoplasmic Reticulum. What does this indicate about the function of these cells? 4 Sketch a chloroplast and a mitochondrion. Label the membranes and compartments. 5 a. As part of which cellular structure would you expect to find microfilaments, microtubules and intermediate filaments? b. Apart from the answer to part a) in which other structure would you expect to find microtubules? 6 Prioritise the completion of your glossary words for this topic. It is highly important that you able to name and describe the structure and function of organelles. Congratulations, another chapter completed! Which of the learning outcomes have you achieved? Check them off on your learning outcomes checklist at the start of this chapter. Unit 1.1. Cells Date 01122023 76 Revision | 6 BIOLOGY PROGRAM Chapter 3 | What are biological membranes? Key Concepts Fluid mosaic model – Phospholipid bilayer and proteins Selective permeability – Some molecules can pass through the membrane others can’t How do molecules get across membranes? Each of our cells is surrounded by a complex membrane that functions as a biological border, letting ions and nutrients such as salt, potassium and sugar in and out. The guards are membrane proteins, which do the hard i) PASSIVE TRANSPORT - Diffusion, work of permitting or blocking the traffic of these molecules. osmosis, facilitated diffusion ii) ACTIVE TRANSPORT https://scitechdaily.com/new-findings-on-water-wires-contradict-computational-models-that-have-been- iii) BULK TRANSPORT - Exocytosis / accepted-for-decades/ Endocytosis Unit 1.1. Cells Date 01122023 77 Revision | 6 BIOLOGY PROGRAM  Learning Outcomes On completion of this topic students should have achieved the following learning outcomes: Level of Section Outcome achievement Describe the basic structure of a biological membrane including the phospholipid bilayer, integral proteins and 3.1 peripheral proteins. Identify, draw and label these structures on a simple diagram. Distinguish between cell membrane, as being the outer boundary of the cell, and other membranes, as being the 3.1 boundary or part of internal cellular structures. Understand that all biological membranes have similar structures but their location affects their function. 3.1 Explain what is meant by the term, ‘fluid mosaic ’with regards to membrane structure. Describe what is meant by the term, ‘semi-permeable ’with regards to membrane function. Explain using examples why 3.2 some molecules can cross membranes freely while others cannot. Describe each of the following main methods of transport of substances across a membrane: Diffusion (including osmosis as a specific type of passive transport); Facilitated diffusion; Active transport, 3.3 Bulk transport. Including, a description of the direction of movement across a concentration gradient; if a transport protein is used or not; if energy is required or not, and an example of a molecule moved for each of these three methods of movement. When presented with a described example of transport, identify the mode of transport used and justify your answer. 3.3 Define and correctly apply the terms, hypotonic, isotonic and hypertonic Unit 1.1. Cells Date 01122023 78 Revision | 6 BIOLOGY PROGRAM  Chapter 3 Index Section Section title Page 3.1 Biological membranes 80 3.2 Membranes are selectively permeable (or semi permeable) 82 3.3 How do molecules get across membranes? 83 Unit 1.1. Cells Date 01122023 79 Revision | 6 BIOLOGY PROGRAM Section 3.1 | Biological membranes All living cells are surrounded by a membrane, which separates the cell from its environment. Its main role is to regulate the passage of molecules in to and out of the cell. In eukaryotic cells internal membrane bound compartments (organelles) are present. The structure of cell membrane and internal membrane is the same and is described by the Fluid Mosaic Model. Thickness of the membrane varies. For example, plasma membrane is thickest ~9nm, whereas ER membranes are thinnest ~6nm. Different membranes may be composed of different types of phospholipids. Membranes are asymmetric that is, the properties on one side may differ to the other. Elements of cytoskeleton (microfilaments and microtubules) are associated with the inner surface of the cell membrane and these provide structural support. On the outer surface carbohydrates associated with proteins, or lipids may be present. These may be involved in cell recognition or adhesion to other cells. Figure 3.1 Eukaryotic cells have a cell (plasma) membrane and internal membrane bound organelles (https://www.toppr.com/content/concept/eukaryotic-cell-200275/) Unit 1.1. Cells Date 01122023 80 Revision | 6 BIOLOGY PROGRAM The Fluid Mosaic Model Cell membranes are composed of fluid layer of phospholipids with proteins that are either attached to the surface or embedded in the bilayer. Peripheral proteins - loosely associated with the membrane surface. Removed relatively easily by washing with mild salt solutions. Integral proteins – embedded in the bilayer. Some extend right through the membrane - these are transmembrane proteins. This fluid-mosaic model was developed by Singer and Nicholson in 1972. The bilayer may contain other types of lipid including cholesterol. The cholesterol helps to support this fluid membrane structure. The proteins and phospholipids are able to move around in the bilayer. Figure 3.2 The fluid mosaic model of biological membrane structure. (http://meliasasbio.blogspot.com/2015/03/fluid-mosaic-model.html) Unit 1.1. Cells Date 01122023 81 Revision | 6 BIOLOGY PROGRAM Section 3.2 | Membranes are selectively permeable (or semi permeable) Some molecules pass through the membrane while others do not. This allows cells to control their internal composition. Figure 3.3 | Biological membranes are selectively permeable (Knox et al., 2005) Unit 1.1. Cells Date 01122023 82 Revision | 6 BIOLOGY PROGRAM Section 3.3 | How do molecules get across membranes? (i) PASSIVE TRANSPORT Diffusion Diffusion is the movement of a substance (ie. gases, molecules, ions and liquids) from a region of high concentration of that substance to a region of low concentration of that substance (referred to as a concentration gradient). Substances may move across membranes by diffusion if the membrane is permeable to the substance. Each molecule diffuses down its own concentration gradient. It is not affected by the concentration gradients of other molecules. No energy expenditure is required. Unit 1.1. Cells Date 01122023 83 Revision | 6 BIOLOGY PROGRAM  Figure 3.4 | A substance will move from a region of high concentration to low concentration by diffusion (https://content.byui.edu/file/a236934c-3c60-4fe9-90aa- d343b3e3a640/1/module5/readings/membrane_transport.html) Unit 1.1. Cells Date 01122023 84 Revision | 6 BIOLOGY PROGRAM Osmosis Osmosis is the net movement of water molecules across a selectively permeable membrane from a region of higher water concentration to a region of lower water concentration. Osmosis