Holiday Revision PDF

1.1 Forgot name ➔ Matthias Schleiden → Nucleus (1838) ➔ Antonie van Leeuwenhoek → bacteria (1670) ➔ Theodor Schwann → cells have individual life of own (1839) ➔ Cell theory 1849, Rudolf Virchaw later said cells come from cells and aren't “created” Prokaryotic vs. Eukaryotic ➔ Al...

1.1 Forgot name ➔ Matthias Schleiden → Nucleus (1838) ➔ Antonie van Leeuwenhoek → bacteria (1670) ➔ Theodor Schwann → cells have individual life of own (1839) ➔ Cell theory 1849, Rudolf Virchaw later said cells come from cells and aren't “created” Prokaryotic vs. Eukaryotic ➔ All living things= Kingdoms (Animal, plant, fungi, protista, eubacteria, archaebacteria) which are originally based on being either prokaryotic or eukaryotic Prokaryotic ➔ Found in eubacteria and archaebacteria ➔ No membrane bound (surrounded by a membrane/wall) organelles internally, nucleus or, compartment ➔ DNA not in nucleus → packaged together with proteins in a region called nucleoid, and as extra chromosomal DNA in plasmids Eukaryotic ➔ Has membrane bound organelles suspended in cytosol ➔ DNA enclosed in in nucleus (nuclear envelope) DNA codes for protein synthesis  1.2 Size and shape Surface area and volume ➔ A cell needs to have enough space to remove toxins and gain requirements/nutrition → plasma membrane must be big enough ➔ A larger SA than V is required for a healthy cell, a ratio of 3:1 is better than 2:1 More Entry and Exit Points: A larger surface area provides more space for molecules (like oxygen, nutrients, and waste) to pass through the cell membrane. This means more molecules can diffuse at the same time. Reduced Distance for Diffusion: In a smaller cell with a high surface-area-to-volume ratio, the distance that molecules need to travel inside the cell is shorter. This speeds up the distribution of nutrients and removal of waste. Proportional Supply to Demand: Cells consume nutrients and oxygen in proportion to their volume (the "demand"). When the surface area is large relative to the volume, the "supply" (the rate at which these substances can enter or leave the cell) keeps up with the demand. Minimizing Congestion: With more surface area, molecules can move across the membrane without causing "traffic jams" that might slow down the overall diffusion process. ➔ Volume of a cell grows faster than SA: as a cell grows, the ratio difference decreases. Meaning that the efficiency of obtaining nutrients and removing waste also reduces. The cell reaches a point where the movement of substances by diffusion isn’t enough to aid the growth of a cell. THIS IS WHY CELLS ARE SO SMALL. How big can cells grow ➔ An egg yolk is one cell ➔ To escape the matrix, the vacuole in algal cells gets VERY large, pushing the active cytoplasm (describes cytoplasm which holds organelles and carries out chemical reaction, basically the cytoplasm) to the cell’s edge. 1. Thru this, the distance materials move to diffuse when going in and out is less  2. Reduces active volume of cytoplasm= reduces amount of exchange occurring across membranes. (bcoz cytoplasm controls things coming in and out of the cell) 1.6 This is because there are fewer organelles as the active cytoplasm is reduced. Shapes of cells ➔ Some cells need to be a certain shape to carry out functions ➔ Spheres have the least SA: V ratio ➔ Some cells have specific features to give them more surface area: root hairs 1.3 What’s inside? ➔ Membrane-bound organelles=greater surface area Amino Acids ➔ Protein building blocks ➔ Are of 2 types: essential and non essential Essential: Ones we can not produce naturally, and we get from our diets (10) Non essential: Ones that our bodies produce (10) ➔ Our body has 20 amino acids to play with, DNA decides amino acid order https://youtu.be/gG7uCskUOrA Enzymes ➔ Special proteins that increase the speed a reaction takes place by reducing the amount of energy needed ➔ Each enzyme fits only a certain molecule/s known as substrates (what is changed in a reaction) Structure ➔ Have a specific site called ACTIVE SITE → where the substrate binds Has a specific size, shape and chemical behaviour bcoz of specific amino acid arrangements ➔ Enzymes also consist of a non protein part called cofactors. Many enzymes only perform their catabolic role when assigned a coenzyme (cofactor). These can be: cation → positively charged metal ions which ‘activate’ the enzyme, temporarily bound Organic molecules like vitamins or vitamin products (coenzymes) which join temporarily Prosthetic groups permanently enzyme bound ➔ An inactivated enzyme (Apoenzyme) along with a coenzyme make up a system called a holoenzyme. There is 2 types of reactions: catabolic and anabolic ➔ Catabolic→large molecules split into smaller ➔ Anabolic → smaller molecules join to form one larger molecule Plasma membrane ➔ Separates other cells ➔ Composed of lipid molecules with tiny protein channels (nutrient, waste, water enter and leave through these) Cytoplasm ➔ Cytosol → gel like fluid which suspends organelles and dissolves substances ➔ Cytoplasm → holds cytosol and organelles, although not the nucleus, carries out chemical reactions Nucleus ➔ Control centre ➔ Includes mainly DNA: DNA codes for proteins, in this way the nucleus can coordinate activities depending on cell function Separated from the rest of the cell by a nuclear membrane (made of fatty lipid with pores, allowing charged particles (ions) and molecules to move across it. In this way the DNA is separated from cytoplasm reactions ➔ Nucleolus → The site of ribosome synthesis made up of a densely packed protein and a type of nucleic acid called RNA ➔ Nuclear envelope → keeps everything where it should be, and has pores which decide what goes and comes Mitochondria ➔ Mitochondria → site of aerobic cellular respiration, release energy for cells Cellular respiration → series of chemical reactions in which glucose is metabolised in the presence of water to produce carbon, water, and heat energy ➔ During some stages of these chemical reactions, energy is released to join inorganic phosphate into ADP molecules to form ATP ATP → energy storage molecule used for cellular processes Energy is released from ATP when the bond in the final phosphate is broken to form ADP ➔ Cristae → the folds in the inner membrane of the mitochondria. They are the site of chemical reactions (like production of ATP) (more wobbles = more energy) ➔ Mitochondria have their own DNA and ribosomes! Because the cytoplasm of the mothers egg turns into the cytoplasm of the zygote, producing a unique mitochondrial DNA. The sperm only gives you your nuclear DNA. THIS MEANS THAT A MITOCHONDRIA CAN REPLICATE ITSELF Ribosomes ➔ Ribosomes: build up proteins (synthesise) from amino acids Proteins are needed for cell growth, repair and cell function Structure ➔ Are made of two subunits which are made of RNA and protein, they stay separated until needed to join The smaller subunit in eukaryotic cells is 40s and the larger is 60s. The smaller subunit includes 18s rRNA and 30 proteins. The larger subunit contains 3 different rRNAs: 28s, 55s, 5.8s, and 40 proteins. ➔ The two subunits join together and squash the messenger RNA to make proteins (https://youtu.be/gG7uCskUOrA Endoplasmic Reticulum ➔ Endoplasmic reticulum → produce, process, and delivers proteins to other parts of the cell ➔ Pinches off into small sacs called vesicles, the endoplasmic reticulum is an intracellular transport system which helps move proteins in the cell ➔ with ribosomes is called rough endoplasmic reticulum. Proteins produced here move directly into the endoplasmic reticulum internal compartment where they can have modifications added and be transported around the cell Proteins produced here can also be secreted OUT of the cell, like enzymes and hormones. The endoplasmic reticulum also helps move proteins to other cells ➔ Smooth endoplasmic reticulum does not have ribosomes and INSTEAD makes lipids Their purpose depends on the type of cell. Mainly, it is to transport proteins, synthesize lipids and assist in the making of plasma membrane In liver cells: detoxifies drugs In adrenal cortex cells: produces steroid hormones Is a place for calcium ions, necessary for muscle contraction and membrane protein interaction Golgi Apparatus ➔ Golgi Apparatus → transport, sorting and modification of both protein and lipid. ➔ Made up of membranes in the cytoplasm ➔ Composed of typically 4-8 flat stacked pouches called cisternae, which stick together with matrix proteins, supported by microtubules ★ To secrete protein out of the cell → a transport vesicle from the ER containing protein pinches of the ER and fuses with the GA, releasing the contents of the vesicle into the GA. Then, a  transport vesicle of the GA pinches off the GA , fuses with the plasma membrane and secretes the proteins Consider a grass eating animal like a kangaroo: Grass cells have a tough outer membrane. To digest and get nutrients from the grass, the cell wall must be broken by enzymes. 1. These are produced in the animal's digestive glands, and digestive enzymes are produced initially in the on the rough endoplasmic reticulum. 2. Enzyme moves through the channels within the endoplasmic reticulum where it goes through the vesicle. 3. The vesicle fuses into the golgi apparatus and releases the enzymes into it. 4. Different enzymes put the final touches to the digestive enzyme and then it is stored and released into the kangaroo’s intestines. Lysosomes ➔ Formed by Golgi Apparatus ➔ Responsible for reusing organelles that have worn out through the use of digestive enzymes and acidity to break down complex chemical compounds (like proteins into amino acids). These broken down compounds are used to make new compounds and organelles ➔ Can also digest external substances which are brought into cell Cytoskeleton ➔ Cytoskeleton → 3 dimensional structure that provides shape to the cell ➔ The ‘bones’ are structures called microtubules and microfilaments made up of actin and tubulin ➔ Microtubules → hollow cylindrical tubes (20 nanometres in diameter) that determine cell shape and provide a set of rails for organelles to travel on. Cytoplasmic streaming → the constant movement of organelles around the cell Microtubules are capable of coming apart and coming back together in an area of the cell where they are needed. Centrioles are organelles which also produce and organize microtubules. Centrioles divide in cell division and give rise to spindle fibres → collections of microtubules onto which chromosomes attach ➔ Microfilaments → can cause cell to change shape (like muscle cells contracting) ¼ the size of a microtubule, easily assembled and disassembled, occur in bundles ➔ Prokaryotic cells also have a cytoskeleton made of similar proteins Cell walls ➔ Plant, bacteria, fungi and algae cells have an extra cell wall which is composed of cellulose Cellulose → complex carbohydrate molecule Plastids ➔ Cause the colourful presentation of plants. ➔ 3 different types of plastids: chloroplasts, leucoplasts (no colour), and chromoplasts (red) Chloroplasts ➔ Photosynthesis → process by which plants convert light to chemical energy Occurs in the stroma and thylakoid membrane system of the chloroplast. These are folded many times to provide more surface area for reactions to occur in. They are also associated with enzymes necessary to speed up chemical reactions involved. ➔ A chemical called chlorophyll absorbs light energy Vacuoles ➔ Stores sugars water minerals and proteins ➔ Can take up 50-90% of cell volume. As the organelle increases, more pressure is put on the cell wall making it bulge and making the cytoplasm become like a narrow band. 1.4 Plasma Membrane ➔ Plasma membrane → controls exchange of materials and messages in and out of the cell ➔ Forms a boundary between internal environment of cell, cytoplasm and its surroundings ➔ Animal cells are surrounded by a plasma membrane, and plants cells also have a cell wall ➔ Cell wall adds support and strength, but is permeable (allows things to pass through), while the plasma membrane is selectively permeable Structure of the plasma membrane ➔ Made up of small phospholipid molecules which make the cells plasma flexible and reshapable ➔ The plasma membrane is made of phospholipid molecules, best described as having a head and 2 tails The head is a hydrophilic ( allow water soluble substances to move through) phosphate group, and the tail is a hydrophobic (allow water insoluble substances to pass through) fatty acid ★ This means that the head can remain in water but the tails are repelled from aqueous  solutions, forcing them to form a wall in which they face against each other, forming a phospholipid bilayer ➔ Individual molecules are capable of sideways movement The bilayer is neither solid nor liquid, more like a liquid crystal They also travel rapidly ➔ Specialised protein molecules are embedded in the bilayer at different intervals and can move sideways, while some are fixed. Sterols increase flexibility Phospholipids are not the only things that make the membrane flexible, as strong inflexible bonds tend to form between their tails ➔ In animal cells, another type of lipid called cholesterol is spread in the bilayer ★ It interferes with interactions between lipid tails ➔ Depending on temperature, cholesterol has an interesting effect on membrane fluidity In low temperatures, phospholipid molecules cluster together and fluidity is reduced. When cholesterol is inserted, fluidity increases due to increased space between molecules In high temperatures, fluidity is increased. When cholesterol is inserted, the energy and motion of the tails is reduced and fluidity is decreased. In this way, the fluidity of the plasma membrane is controlled ➔ In plants, there is phytosterol Membrane proteins Each membrane has its own associated proteins which allow for it to do its distinct activities. ➔ The type of proteins attached differ based on cell type and location, even the two layers of the bilayer vary ➔ The way proteins are associated with the cell also vary, some are bound only to the membrane surface, while others are embedded in the bilayer, and may penetrate to the other side Surface proteins= cell-cell communication and interaction, and exchange of substances with external environment Proteins on external plasma= signalling and communication between cells and keep cell anchored to appropriate place Proteins that span the membrane (transmembrane proteins)= regulate movement of substances across membrane ➔ Different cell type = different receptor proteins → a protein that binds hormone and other signal molecules Receptor cells are determined by genetic information Membrane proteins are essential for regulating cell behaviour, communication and organisation of cell tissues. A few types include: ➔ Some proteins (receptors) have receptor sites on their surface that detect molecules (like hormones) Each receptor is specific to a hormone or molecule Some membrane receptor proteins carry a carbohydrate molecule → glycoprotein ➔ Recognition protein molecules identify the cell as a normal body cell belonging to YOU ➔ Adhesion proteins link cells together to maintain the structure of tissues. They are uniformly distributed along the membrane 1.5 Passive movement across membranes Some materials require energy to move while others don't ➔ Movement that does not require energy is called passive transport, it relies on a process called diffusion Diffusion ➔ Diffusion → the net movement of particles form a region of high concentration to low concentration The difference between the two regions in particle concentration is called concentration gradient Equilibrium → the point where particles are evenly distributed, and they move at equal rates Diffusion across membranes ➔ Some uncharged particles easily pass through the membrane Facilitated diffusion ➔ Charged ions (like sodium+ ) and large molecules (like glucose) are repelled by the hydrophobic tails of the bilayer To let such particles enter, there is special proteins which shield these materials from the hydrophobic tails and let them enter the cell →facilitated division Two types of proteins are involved in facilitated division: Carrier proteins: bind to molecules on one side of the bilayer by changing shapes, and release the molecule on the other side Channel proteins: water soluble substances pass through these. The inner boundaries of this protein have layers of water so that hydrophilic substances can move easily. Only ions of specific characters can move through certain channel proteins. Osmosis: a special type of diffusion ➔ Plasma membranes are selectively permeable. Water molecules pass more easily than solutes. Osmosis → diffusion of water by movement from an area of high concentration to an are of low concentration  ➔ If fluids inside and outside are equal, the external solution is said to be isotonic (iso=same) ➔ When cells are surrounded by a solution that contains a lower solute concentration than their cytoplasm, the external solution is said to be hypotonic (hypo =lower) ➔ Cell surrounded by a solution of high concentration is hypertonic (hyper= high) Osmosis in animal cells