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BIO101 LEC Lesson 2: Cell Structure and Function Cell Organelles and the Cell Activity Learning Outcomes 1 2 3 Explain how the Identify the four main Decribe the cell structures of a cell functions of a cell and membrane and th...

BIO101 LEC Lesson 2: Cell Structure and Function Cell Organelles and the Cell Activity Learning Outcomes 1 2 3 Explain how the Identify the four main Decribe the cell structures of a cell functions of a cell and membrane and the contribute to its the whole cell activity different movements function. across it. Whoa! Did you know? There are approximately 36 trillion cells in the human body. Important Facts: Neurons/ nerve cells are the LONGEST cells in the human body, as well as the longest living cells. Sperm cell is the SMALLEST cell. Egg cell/ ovum is the LARGEST cell. Red blood cells can live up to 120 days but white blood cells can only live for about 13 days. What is a cell?  Introduction The cell is the basic unit of all organisms. It is like a factory filled with workers (organelles) doing different jobs. Simple organisms such as bacteria, are composed only of one cell (prokaryotes). However, humans, plants, and animals are composed of multiple cells (eukaryotes).  Why do we need to study about the cell?  Why do we need to study the cell? The human body is composed of cells. Thus, we must first understand how cells and its organelles work before we can understand the anatomy and physiology of the human body. 1 Cell Structure Its Organelles and their Functions  Cell Membrane /Plasma Membrane ⮚ Outermost component of cell ⮚ Encloses the cytoplasm; forms boundary between material inside the cell and outside the cell. ⮚ Cell membrane is made up of 2 major type of molecules; Phospholipids and Proteins. In addition, it also has cholesterol and carbohydrates.  Nucleus ⮚ Is the command/control center of the cell located near the center and contains the DNA. ⮚ It is bounded by the Nuclear envelope – consist of outer and inner membrane with narrow space between. ⮚ It is the site for RNA synthesis. ⮚ Discovered by Robert Brown. ⮚ Largest organelle in an animal cell.  Nucleus ⮚ At some point on the surface of nucleus the outer and inner membrane come together to form nuclear pores - Through which material can pass through in/out nucleus. ⮚ The nuclei of human cells contain 23 pairs of chromosomes – carrying genetic info in the form of genes, which contains DNA and proteins  Nucleus ⮚ Chromatin – chromosomes that are loosely coiled ⮚ Chromosomes- tightly coiled as preparation for cell division. It can be seen under the microscope. ⮚ Chromatids- one copy of a newly copied chromosome during cell division (sister chromatids) ⮚ Genes that influences the structural and functional features of every individual are positive of DNA molecules  Ribosomes ⮚ an organelle that functions as a micro-machine for producing proteins. ⮚ Ribosomes may be attached to other organelles in the cell such as the Endoplasmic Reticulum. ⮚ Ribosomes that are not attached to any organelle are called: Free ribosomes  Endoplasmic Reticulum ⮚ a series of membranes forming sacs and tubules that extends from the outer nuclear membrane into the cytoplasm. It serves as a channel (highway) through which materials are transported. ⮚ Rough ER - ribosomes are attached, major site for protein synthesis ⮚ Smooth ER - without ribosomes, major site for lipid synthesis  Golgi Apparatus ⮚ Series of closely packed membrane sacs that collect, modify, package and distribute proteins and lipids produced by ER. ⮚ Golgi Apparatus chemically modifies protein by attaching carbs/lipids ⮚ Golgi Apparatus are present in larger numbers and most highly develop in cells that secret protein such as Salivary Glands and Pancreas.  Secretory Vesicles ⮚ are membrane bound sacs that carry substances from GA “those that are pinched off” to cell membrane, where vesicle contents are released ⮚ In many cells, secretory vesicles accumulate in cytoplasm and are released to exterior when cells receive signals.  Lysosomes ⮚ are membrane-bound vesicles formed from the Golgi apparatus that breaks down or digests phagocytized material (bacteria, foreign substances, worn-out cell parts). ⮚ Like a garbage collector of the cell.  Mitochondria ⮚ the major sites of adenosine triphosphate (ATP) production within cells and it carries out cellular respiration; a series of chemical reactions that require O2 to break down food molecules to produce ATP. ⮚ ATP - is the main energy source for most chemical reactions within the cell. Cells with a large energy requirement have more mitochondria than cells that require less energy.  Cytoskeleton ⮚ supports the cytoplasm and organelles and its involved with cell movements ⮚ composed of microtubules, microfilaments and intermediate filaments ⮚ Like skeleton of the body acts as internal framework of the cell Cytoskeleton ⮚ consist of protein structures that support the cell ⮚ holds organelles in place ⮚ enable the cell to change shape  Centrioles ⮚ are located in the centrosome that are made up of microtubules. ⮚ They facilitate chromosome movement during cell division. ⮚ Centrosome- a specialized region in the cytoplasm where microtubule formation occurs. ⮚ Each centrosome has 2 centrioles, and each centriole is composed of microtubule organized into 9 triples, each triplet consist of 3 parallel microtubules joined together Cilia, Flagella, and Microvilli ⮚ Cilia (an eyelash) move substances over the surface of the cells ⮚ Flagella (a whip), one per cell, are much longer than cilia and propel sperm cells ⮚ Microvilli (shaggy hair) increase the surface area of cells and aid in absorption ⮚ Cilia vary in number from 0 to thousands per cell ⮚ Cilia are numerous on surface cells that line the respiratory tract Movement through the Cell Membrane Passive and Active Transport 2 Cell Membrane ⮚ Selectively permeable - allows SPECIFIC substances to pass into and out of the cell ⮚ Movement through cell membrane may be passive or active. Cell Membrane ⮚ Phospholipid bilayer – acts as barrier to most water-soluble substances ⮚ Certain water-soluble substances can diffuse between phospholipid molecule of membrane other water-soluble substances such as ions can diffuse across cell membrane only by passing through cell membrane channel ⮚ Molecules that are lipid-soluble such as O2 and CO2 and steroids pass easily through phospholipid bilayer. Cell Membrane ⮚ There are two types of channels in the cell membrane; leak channels and gated channels. ⮚ Leak Channels – allows ions to pass through ⮚ Gated Channels – limit movement of ions across membrane by opening/closing  What are the molecules that can be found in the cell membrane? 1. Phospholipids ⮚ Phospholipids has fluid quality meaning they are not completely stationary but able to move ⮚ Hydrophobic tail (water-fearing) ⮚ Hydrophilic head (water-loving) 2. Proteins ⮚ Membrane channel and carrier molecules ⮚ involved with the movement of substances through cell membrane (facilitates) ⮚ membrane protein function as membrane channel 3. Cholesterol ⮚ Cholesterol – gives phospholipid added strength and stability by limiting the amount of movement 4. Receptor Molecules ⮚ part of intercellular communication system that enables cell recognition and coordination of cell activites. Passive Transport ⮚ Diffusion – solutes such as ions/molecules tend to move from higher concentration of a solute to an area of lower concentration o Solute – dissolved in a predominant liquid/ gas o Solvent – substances that dissolves solute Concentration Gradient ⮚ When we say that a substance moves down the concentration gradient, we mean that solutes are diffusing from a higher toward a lower concentration of solutes. ⮚ When we say that a solute moves up its concentration gradient, this means that the substance moves from an area of lower solute concentration to an area of higher solute concentration. This second type of movement does not occur by diffusion and requires energy in order to occur. Osmosis ⮚ Osmosis- the diffusion of water (a solvent) across a selectively permeable membrane, from a region of HIGHER water concentration to one of LOWER water concentration. ⮚ This process is important to cells because large volume changes caused by water movement can disrupt normal cell functions. Types of Osmotic Conditions When placed into a solution, a cell may swell, remain unchanged, or shrink, depending on the concentration gradient between the solution and the cell’s cytoplasm. 1. A hypotonic solution usually has a lower concentration of solutes and a higher concentration of water relative to the cytoplasm of the cell. Water goes inside the cell causing it to swell/burst/turgid. Types of Osmotic Conditions 2. Isotonic solution - When a cell is immersed in an isotonic solution, the concentrations of various solutes and water are the same on both sides of the cell membrane. The cell therefore neither shrinks nor swells. Types of Osmotic Conditions 3. Hypertonic solution- When a cell is immersed in a hypertonic solution, the solution usually has a higher concentration of solutes and a lower concentration of water relative to the cytoplasm of the cell. Water moves by osmosis from the cell into the hypertonic solution, resulting in cell shrinkage, or crenation  Carrier-Mediated Transport Mechanism ⮚ Many nutrient molecules such as amino acids and glucose cannot enter cell by diffusion. Likewise, many polar molecules produced in cell cannot leave the cell by diffusion ⮚ Carrier molecules – proteins within the cell's membrane are involved in carrier mediated transport mechanism - “Process of Carrying”  1. Facilitated Diffusion Ø is a carrier-mediated transport process that moves substances across the cell membrane from an area of higher concentration to an area of lower concentration of that substance.  2. Active Transport Ø is a carrier-mediated process that moves substances across the cell membrane from regions of lower concentration to those of higher concentration against a concentration gradient.  2. Active Transport Ø Active transport requires energy in the form of ATP; Ø if ATP is not available, active transport stops.  3. Secondary Active Transport Ø involves the active transport of one substance, such as sodium, across the cell membrane  4. Endocytosis and Exocytosis Ø Large water-soluble molecules that cannot be transported, small pieces of matter and even whole cells Ø They can be transported through membrane bound sacs called vesicles  4. Endocytosis and Exocytosis Ø The cell membrane contains specific receptor molecules that binds to specific substance – Endocytosis is triggered Ø Substances is transported in to the cell. This process is called Receptor - mediated endocytosis  4. Endocytosis and Exocytosis Ø Phagocytosis (Cell eating) is often used for endocytosis when solid particles are ingested Ø Pinocytosis (Cell drinking) if vesicles are formed and contains liquid. The cell takes in fluids with dissolved small molecules.  4. Endocytosis and Exocytosis Ø Exocytosis- Opposite of endocytosis) Ø Material in vesicle is released from the cell Ø In some cells, membrane bound sacs called secretory vesicles accumulate materials for release Ø Cell Functions The Four Main Functions of the Cell 3 1. Cell Metabolism and Energy Use The chemical reactions that occur within cells are collectively called cell metabolism. Energy released during metabolism is used for cell activities, such as the synthesis of new molecules, muscle contraction, and heat production, which helps maintain body temperature. 2. Synthesis of Molecules Cells synthesize various types of molecules, including proteins, nucleic acids, and lipids. The different cells of the body do not all produce the same molecules. Therefore, a cell's structural and functional characteristics are determined by the types of molecules the cell produces. 3. Communication Cells produce and receive chemical and electrical signals that allow them to communicate with one another. For example, nerve cells communicate with one another and with muscle cells, causing muscle cells to contract. 4. Reproduction and Inheritance Each cell conta ins a cop y of the genetic information of the individual. Specialized cells (sperm cells and oocytes) transmit that genetic information to the next generation.  Cell Activity Gene Expression, Cell Cycle, and Cell Death 4 Whole Cell Activity Ø Cells’ characteristics are ultimately determined by the types of protein they produce Ø Protein produced are in turn determined by genetic info in the nucleus Ø Human body is composed of trillions of cells. With many different characteristics. Each human begins life as single cell. Through cell division and cell differentiation. The cells that make up human body is formed Gene Expression Ø is the process by which the genetic code (the nucleotide sequence) of a gene is used to direct protein synthesis and produce the structures of the cell. genes that code for amino acid sequences are known as “structural genes” Ø DNA- contains the information that directs protein synthesis. Deoxyribonucleic Acid Ø this determines individuals color of the eye, hair and other inherited traits. Ø DNA molecules consist of nucleotides joined together to form two (2) nucleotide strands Ø The 2 strands are connected and resemble a ladder. That is twisted around its long axis (double helix)  Genes ⮚ is a sequence of nucleotides that provides a chemical set of instructions for making a specific protein Ø “Recipe” for making protein ⮚ Each DNA molecule contains different genes