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St Ninian’s High School Biology Department National 5 Unit 1: Cell Biology Summary Notes Name: _______________________ Cell Ultra Structure A cell is the basic unit of life. There are 4 main types of cells to learn in National 5 Biology. Animal Cells Animal cell has 5 key parts. Ribosomes Mitochondria Cytoplasm Nucleus Cell membrane Plant Cells Plant cell has 8 key parts. Vacuole Cytoplasm Hint! Don't get mitochondria and chloroplasts confused! Mitochondria = wiggly line in middle Chloroplast Chloroplast = stacks of discs Mitochondria Nucleus Ribosomes Cell wall Cell membrane Cell Ultra Structure Yeast Cell Yeast cell has 7 key parts. Ribosomes Mitochondria Cell wall Vacuole Cell membrane Cytoplasm Nucleus Bacterial Cell Bacterial cell has 6 key parts. Plasmid Ribosomes Cytoplasm Cell membrane Cell wall Free-floating DNA Cell Ultra Structure Cell Part Function Cells Ribosomes Site of protein synthesis All Cytoplasm Where chemical reactions occur All Cell membrane Controls what enters and leaves the cell All Nucleus Controls all cell activities Animal, plant and yeast Mitochondria Site of aerobic respiration Animal, plant and yeast Cell wall Supports the cell Plant, bacteria and yeast Vacuole Stores cell sap Plant and yeast Chloroplasts Site of photosynthesis Plants only Plasmids Passed naturally between bacteria. Extra circular piece of DNA. Bacteria only Free floating DNA Genetic material that codes for protein Bacteria only Cell Microscope Calculation Calculate the average length of the cells in micrometres. (1mm = 1000 micrometres) 10 mm divided by 5 cells = 2mm per cell Convert mm into micrometres. 2 x 1000 = 2000 micrometres 10mm length Remember... width Cell Membrane Function of the membrane Controls what enters and leaves the cell. Selectively permeable Only allows small molecules to move in and out of cell, but NOT large molecules. Small molecules Oxygen Water Carbon dioxide Glucose Amino acids Fatty acids and glycerol Large Molecules Proteins Fat Starch Large molecules require to be digested by enzymes before they can pass through the membrane. Proteins Structures in the membrane 1. Phospholipids 2. Protein Phospholipids Transport across the Membrane Molecules can move across the membrane in TWO ways. 1. 2. Passive transport (diffusion and osmosis) High to low concentration (down the concentration gradient). No energy required. Very slow process due to no energy needed. Active Transport Low to high concentration (against concentration gradient). Energy required to allow membrane proteins to move molecules from low to high concentration. Importance of Diffusion in everyday life Oxygen/glucose diffuse INTO cells for respiration. Carbon dioxide & water diffuse OUT of cells as waste products produced by respiration. Osmosis in Cells Animal Cells Animal cells are surrounded only by the membrane, therefore they either burst or shrink depending on their surrounding solutions. Pure Water Salt/Sugar Water HWC HWC LWC LWC Animal cells will gain mass. Animal cells will lose mass. Cell will SWELL & BURST. Cell will SHRINK. Plant Cells Plant cells are surrounded by a cell wall which prevents cell bursting or shrinking. Pure Water Salt/Sugar Water Turgid plant cell 1. Vacuole gets bigger (stores water). 2. Cell membrane pushes against the cell wall. Plasmolysed plant cell 1. Vacuole gets smaller (loses water). 2. Cell membrane pulls away from the cell wall. Summary of Animal/Plant Cells Type of Cell Strong Salt Solution Pure water Animal Shrink Burst Plant Plasmolysed Turgid Osmosis Problem Solving What is osmosis? A special case of diffusion involving water molecules. Water molecules move from areas of high WATER concentration to areas of low WATER concentration through a selectively permeable membrane. Osmosis In Cells Cell placed in pure water; Cell placed in strong salt/sugar solution; Gain mass Lose mass High water concentration outside the cell to low water concentration inside the cell High water concentration inside the cell to low water concentration outside the cell *****Likely 2 mark exam question***** Q. Explain what happens to the following cells in terms of water movement. A Pure water Water moves into the cell by osmosis (1 mark) from an area of high water concentration outside the cell to an area of low water concentration inside the cell (1 mark). B Strong salt solution Water moves out of the cell by osmosis (1 mark) from an area of high water concentration inside the cell to an area of low water concentration outside the cell (1 mark). Hint! Think....where’s the high water concentration, where’s the low water concentration. Osmosis Problem Solving Possible exam question Q. Why should you blot the plant tissue dry before starting an osmosis experiment? A. Blotting tissue sample prevents excess/ external water being taken into account. Problem Solving Calculating percentage change (also called percentage increase/decrease) change X 100 original Worked Examples 1. A plant cell is placed in pure water. The plant cell weighed 12g before, and now weighs 15g after osmosis has occurred. Calculate the percentage change in mass. Change = 15-12g = 3g Original number = 12g (3÷12) x 100 = 25% 2. A plant cell was placed in a 20% salt solution, and as a results now weighs 4g. If the plant cell originally weighed 10g, calculate the percentage change in mass. Change = 10-4g = 6g Original number = 10g (6÷10) x 100 = 60% Mitosis What is mitosis? When 1 diploid cell produces two identical diploid cells. Mitosis maintains diploid chromosome number. Diploid = 2 matching sets of chromosomes 46 46 46 46 46 46 46 Why undergo mitosis? Single celled organisms – reproduction. Multicellular organisms - growth & repair. Location of mitosis In the nucleus (DNA found here) ***Importance of maintaining the number of chromosomes (complement)*** To ensure no genetic information is lost. Mitosis Long uncoiled chromosome, not yet visible. Nuclear membrane breaks down. Chromosomes replicate to form 2 chromatids. Chromosomes are now visible. Chromosomes line up at the equator (middle) of the cell and spindle fibres attach (at centromere). Chromatids pulled to opposite poles (ends) of cell by spindle fibres. Nuclear membrane reforms . Cytoplasm divides. 2 identical diploid daughter cells are produced. Aseptic Technique Aseptic Technique Promote cell division (growth) of 1 microorganism by preventing contamination by other micro organisms. Techniques used 1. Disinfecting working areas 2. Washing hands 3. Use of lab coats 4. Flaming bottle necks in a Bunsen burner Industrial fermenters Containers used to grow micro organisms on a large scale to make useful products such as beer, wine or antibiotics. Fermenters need to control ABIOTIC factors to ensure optimum bacterial growth. These factors include; Temperature Oxygen concentration pH DNA Structure Location of DNA DNA is found in the nucleus of the cell. DNA molecules are made up of nucleotides which have 3 basic parts. phosphate base sugar Structure of DNA The 2 strands of DNA nucleotides are held together in a twisted 3D structure known as a double helix. DNA Bases DNA has four different bases which form complementary base pairs as follows, making up the GENETIC CODE. Adenine (A) Thymine (T) + Guanine (G) Cytosine (C) + Complementary base code example A G T C A G C T (Strand 1) T C A G T C G A (complementary strand 2) DNA Calculations DNA Calculations Your exam paper may ask you to calculate the percentage of A bases given the number of G bases etc. Two worked examples are shown below. Worked example 1 If there are 1200 bases in total and 300 are adenine (A) – how many are cytosine (C)? A - 300 = T – 300 G + C = 1200 – 600 = 600 bases for both G + C Therefore, G = 600/2 = 300 bases Worked example 2 If 10% of 4000 bases are thymine (T), what number are guanine (G)? T - 10% = A - 10% G + C = 80% divide by 2 = 40% are G Now find 40% of the total (4000) 40/100 X 4000 = 1600 bases DNA Function Function of DNA DNA is a genetic code for protein. The Genetic Code A particular protein is made by a particular amino acid sequence, which is determined by the original DNA base sequence (genetic code). Base Sequence (determines) Amino Acid sequence (determines) Protein structure (determines) Protein function Making Proteins DNA cannot leave the nucleus to take the genetic code to the ribosomes to make proteins. Therefore, it makes a single stranded copy of the genetic code which can travel to the ribosomes. This messenger molecule is called mRNA. mRNA (messenger RNA) mRNA is produced in the nucleus from complementary base pairing with one of the two DNA strands. mRNA is identical to DNA except its 4 bases are: A&U C&G mRNA function Takes complementary genetic code from the nucleus to the ribosomes. mRNA DNA A G T C U C A G T C A G A U T mRNA leaves the nucleus and travels through the cytoplasm to the ribosome DNA mRNA U G A ribosome DNA DNA vs. mRNA DNA mRNA Double stranded Single stranded Bases = C & G A & T Bases = C & G A&U C U Making Proteins Ribosomes Once mRNA attaches onto the ribosomes, 3 bases = 1 specific amino acids. This forms a specific amino acid sequence making a specific protein. Different types of protein Proteins are made up of different sequences of amino acids. The different amino acid sequences fold the protein into different shapes giving it a different STRUCTURE and therefore a different FUNCTION. Type of Protein Enzyme Function Speeds up chemical reactions inside cells. Antibodies Fight disease/infections by bacteria. Receptors Bind to specific hormones at target tissue. Structural Provides support. Hormone Chemical messengers that travel in blood from one place to another. Enzymes Enzymes are biological catalysts They speed up reactions but are not used up in the reaction. Importance of Enzymes Enzymes allow reactions to happen at relatively low temperatures (37 °C). Lock & Key Theory Enzymes interact with substrate molecules at the enzyme’s active site to produce a product. (substrate) (products) (substrate fits into enzyme’s active site) (enzyme) The active site is uniquely shaped that only fits 1 type of substrate (lock & key model). Factors affecting enzyme activity 1. Temperature 2. pH Enzymes Enzyme activity with temperature graph Optimum temperature The optimum temperature is the temperature where the enzyme works best. Every enzyme has the same optimum temperature of 37°C. Denatured Enzymes Above 40°C the active site of the enzyme is permanently damaged and the enzyme no longer works. The enzyme is said to be denatured. (normal enzyme) (denatured enzyme) Top tip At low temperatures enzymes do not work very well but they are NOT denatured. This is because if the temperature is increased to the optimum the enzyme will work well again. Enzymes pH The pH scale is a measure of the hydrogen ion concentration and is given a rating 1-14. Acid pH = 1-6 Neutral pH = 7 Alkali pH = 8-14 Enzyme activity with pH graph Different enzymes work best at different pH values, their optimum pH. Many enzymes’ optimum pH is neutral (pH 7) but not all! Pepsin optimum – pH 2 Amylase optimum – pH 7 Pepsin amylase 2 Catalase optimum – pH 9 catalase 7 Enzyme activity 9 1 2 3 4 5 6 7 8 9 10 11 12 pH Denaturing & pH Extremes of pH (strong acid/alkali) can denature the active site of an enzyme, causing the enzyme to become inactive. Enzymes 2 types of enzyme reactions; Degrading reactions 1 large substrate is broken down into smaller products i.e. during digestion substrate enzyme product Substrate Enzyme Product Hint? Hydrogen Peroxide Catalase (liver) Water + oxygen HPCOW Starch Amylase (saliva) Maltose SAM Protein Pepsin (stomach) Amino Acids PPAA Fat Lipase Fatty acids & glycerol FLAG Synthesising Reaction 1 small substrate is joined together to make a larger product. substrate enzyme product Substrate Enzyme Product Hint? Glucose-1-phosphate Phosphorylase Starch G1PPS Phosphorylase only found in plants which stores glucose made during photosynthesis as starch. Genetic Engineering Bacterial Plasmids Bacteria transfer plasmids in two ways; 1. Naturally between bacteria - to pass on a specific advantage between bacteria through sharing plasmids e.g. passing on resistance to antibiotics 2. Genetic engineering of bacteria - a gene from an animal/plant is inserted into the bacterial plasmid to produce the foreign protein in the bacterial cell. Why use bacteria as the host cell? 1. Bacterial cells divide quickly by mitosis. 2. DNA found loose in cytoplasm, easy to modify. Plasmid Free-floating DNA ***Likely problem solving question*** A bacterial cell replicates every 2 minutes. Calculate how many bacterial cells are present after 12 minutes? O mins – 1 bacterium 2 mins – 2 bacteria 4 mins – 4 bacteria 6 mins – 8 bacteria 8 mins – 16 bacteria 10 mins – 32 bacteria 12 mins – 64 bacteria Genetic Engineering Examples of genetically engineered products Insulin for the control of diabetes. Antibiotics such as penicillin to kill bacteria. Growth hormone for dwarfism. Stages of genetic engineering 1. The insulin gene is ‘cut out’ from a human chromosome using enzymes. 2. The plasmid is removed from the bacterial cell and is ‘cut open’ using enzymes. 3. The insulin gene is then inserted into the plasmid which is then put back into a new bacterial cell. 4. The modified bacterial cell is then added to a fermenter, where it divides and produces insulin in large quantities. 5. The insulin produced by bacterial is continually collected and purified. Genetic Engineering Advantage of genetic engineering Can produce large quantities of substances that were difficult to obtain previously. Disadvantage of genetic engineering Controversial as concerns over; 1. GM bacteria passing on antibiotic resistance to other bacteria in the outside environment. 2. GM crops can pass on weedkiller resistance to weeds. Photosynthesis Word Equation LIGHT ENERGY carbon dioxide + water (raw materials) Photosynthesis 1. oxygen (by-product) CHLOROPHYLL + glucose (carbohydrate food product) is a complex series of enzyme controlled steps split into TWO stages; Light Dependent Stage 2. Carbon Fixation Light Dependent Stage Using light energy to a) Join ADP and Pi using light energy to make ATP (chemical energy) which is needed for Carbon Fixation. b) Splitting up water (photolysis) into oxygen (by-product) and hydrogen which is needed for Carbon Fixation. (needed for stage 2) Photosynthesis Energy Conversion Light energy is absorbed by chlorophyll in chloroplasts. The light energy is converted into chemical energy as ATP to be used in Carbon Fixation. Hydrogen & ATP made in Light Dependent Stage taken to Carbon Fixation stage. Carbon Fixation Carbon Fixation consists of several enzyme-controlled reactions which take the form of a cycle. The cycle forms glucose from carbon dioxide by adding hydrogen and ATP from the Light Dependent stage. ATP + Enzymes Fates of glucose made during Carbon Fixation Glucose (for respiration) Starch (storage carbohydrate in leaves) Iodine turns black when starch is present. Cellulose (structural carbohydrate in cell walls in plants ONLY) Photosynthesis—Limiting Factors A limiting factor is simply anything that if increased, increases the rate of photosynthesis. Rate of photosynthesis (units) Photosynthesis has Light Intensity limiting 30 3 limiting factors: Light Intensity no longer limiting Temperature 10 Light intensity 0 Carbon dioxide concentration 20 0 10 20 Light Intensity (units) Limiting factors—worked example 30°C 25% CO2 conc. C 30°C 15% CO2 conc. B 20°C 15% CO2 conc. A Hints! If the line is going up, look down to the bottom axis. If the line is going across, look up to the next line, what’s changed? Limiting factor at points; A = light intensity B = temperature C = carbon dioxide concentration Measuring Photosynthesis Testing Leaf for Starch Plants can be checked to see if they are photosynthesising if they are producing starch in their leaves by using iodine which turns black in presence of starch. Only green leaves that have been placed in the following conditions will produce starch. 1. Plentiful light 2. CO2 present 3. Room temperature (enzymes near their optimum) Measuring the rate of photosynthesis The rate of photosynthesis can be measured by using a pond weed such as elodea. The beaker contains water full of carbon dioxide, with a lamp used to provide light. A heat shield is used to provide the plant overheating and affecting results. The number of oxygen bubbles per minute is then measured. ATP ATP is made up of one adenosine molecule and 3 phosphates (Pi). ATP is made from ADP and Pi. Function of ATP ATP is a high energy molecule that transfers CHEMICAL energy from respiration to reactions that require ATP, such as; Protein synthesis (in ribosomes) Muscle contraction Active transport Aerobic Respiration The chemical energy stored in glucose is converted into ATP using oxygen through a series of enzyme-controlled reactions called aerobic respiration. Glucose + oxygen carbon dioxide + water + energy Aerobic respiration occurs in the mitochondria. More active cells such as brain or sperm cells have more mitochondria to produce more ATP. Aerobic respiration has 2 stages; 1. Glycolysis Glucose is broken down into pyruvate in a process called glycolysis. Occurs in the cytoplasm & no oxygen is required at this stage. 2 ATP produced per glucose molecule. 2. Aerobic Respiration Pyruvate from cytoplasm moves into the mitochondria. Producing water, CO2 and 36 ATP when OXYGEN is present. In total, during aerobic respiration, 38 ATP is produced. Aerobic Respiration Oxygen Net gain of ATP = 2 + 36 = 38 Fermentation Location—cytoplasm Conditions—no oxygen present 2 ATP produced During fermentation glucose is only partly broken down. Glycolysis occurs producing pyruvate which is then converted into either lactate/ lactic acid (animal muscle cells) OR ethanol and carbon dioxide (yeast and plants). Fermentation in Animal muscle cells Produce lactic acid from pyruvate in process called muscle fatigue. Reaction is reversible when oxygen debt is repaid. Fermentation in plant or yeast cells Produces alcohol (ethanol) and carbon dioxide. Reaction is irreversible, alcohol builds up killing the organism. Respiration Measuring Respiration Organism takes in oxygen which can be seen by measuring the time taken for the coloured liquid to be drawn up the tube in a respirometer. The carbon dioxide exhaled is removed by a carbon dioxide absorbing chemical in test tube to ensure oxygen is drawn up the tube. Respiration Summary Table Aerobic Respiration Fermentation 38 ATP 2 ATP Location Cytoplasm then mitochondria Cytoplasm Products CO2 & water Net energy Animal – lactic acid Plants – ethanol & CO2 & yeast