St Andrew s High School, Coatbridge Biology Department. National 5 Unit 1 Cell Biology Summary Notes

Transcription

1 St Andrew s High School, Coatbridge Biology Department National 5 Unit 1 Cell Biology Summary Notes

2 Key area 1.1 : Cell Structure. Key area 1.2: Transport across Cell Membrane. Key area 1.3: DNA and the production of proteins. Key area 1.4: Proteins & Enzymes. Key area 1.5: Genetic Engineering. Key area 1.6: Respiration. Key Area 1.1: Cell Structure Learning Intentions: Cells 1. Identify Cell ultrastructure and Functions cell wall, mitochondrion, chloroplast, cell membrane, cytoplasm, vacuole, nucleus, ribosome and plasmid using examples from typical plant, animal, fungal and bacterial cells. 2. Similarities and differences between organelles within animal, plant, fungal and bacterial cells. 3. Cell wall is made of cellulose in plant cells but of different materials in fungal and bacterial cells. Cells are the building blocks of all living organisms. Organisms made of a single cell, such as bacteria and the fungus yeast, are described as being unicellular. Organisms made of many cells such as animals, most plants and many species of fungi, are described as being multicellular.

3 Animal & Plant Cell Fungal Cell

4 Bacterial Cell How do we view cells? Living organisms are made up of millions of units called cells. Cells are microscopic so to see their structure we need to use microscopes. We can see more structures clearly if we use stains to colour specimens before putting them under the microscope. Stains are coloured dyes that are absorbed by some cell structures but not by others. An example of a stain which is used is iodine solution.

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6 Cell Wall The cell wall which is present in plant cells is made up of the carbohydrate CELLULOSE. Bacterial and fungal cells also have a cell wall which is made up of different materials. Key Area 1.2: Transport across cell membranes Learning Intentions: 1. State the parts of the cell membrane. 2. Describe passive transport and its energy requirements. 3. Describe diffusion and its importance. 4. Give the definition of osmosis. 5. Describe the changes in animal and plant cells when placed in solutions of different concentrations of salt and sugar solutions. 6. Describe active transport and its energy requirements.

7 The arrangement of the phospholipid molecules gives the membrane fluidity (allows it to move). The protein molecule shown in the diagram forms a channel through the membrane, allowing the movement of small molecules in to and out of the cell. Diffusion Diffusion is the movement of molecules (or ions) from an area of high concentration to an area of low concentration, down a concentration gradient. Examples of molecules that move by diffusion are glucose, oxygen and carbon dioxide. Large molecules like starch cannot leave the cell by diffusion. Diffusion is important as it allows essential molecules like glucose and oxygen enter a cell, whilst removing waste molecules like carbon dioxide. Osmosis Osmosis is the movement of water from an area of high water concentration to an area of low water concentration through a selectively permeable membrane. A cell would decrease in mass if it was placed in a solution containing a strong salt or sugar concentration (low water concentration), as water molecules would leave the cell by moving from an area of high water concentration to an area of low water concentration, and therefore leave the cell. An animal cell would shrink in this case, and a plant cell would become plasmolysed. A cell would increase in mass if it was placed in a solution containing a low salt or sugar concentration (high water concentration), as water molecules would move from an area of high water concentration to an area of low water concentration, and enter the cell. A plant cell would swell, become turgid in this instance, and an animal cell would burst. A plant and animal cell would remain unchanged if it was placed in a solution containing equal water concentrations found both inside and outside the cell. Do these passive processes require energy? Diffusion and osmosis are both passive processes, i.e., they don't need energy; the molecules move down a concentration gradient. A concentration gradient exists when there is a difference in concentration between the inside and outside of a cell.

8 High Concentration Low Concentration Active Transport Active transport is the movement of molecules against a concentration gradient. The molecules move from an area of low concentration to an area of high concentration. Active transport requires energy. Proteins are found in the cell membrane and are responsible for moving molecules across the cell membrane by active transport.

9 Key Area 1.3: DNA and the production of proteins Learning Intentions: 1. To state that DNA has a double- helix structure held by complementary base pairs. 2. To state that DNA carries the genetic information for making proteins. 3. Know the 4 bases, Adenine (A) Thymine (T) Cytosine (C) and Guanine (G) that make up the genetic code. 4. State that Adenine always pairs with Thymine. 5. State that Guanine always pairs with Cytosine. 6. State that the base sequence determines the amino acid sequences in proteins. 7. State that a gene is a section of DNA which codes for a protein. 8. State that Messenger RNA (mrna) is a molecule which carries a complimentary copy of the genetic code from the DNA, in the nucleus, to a ribosome, where the protein is assembled from amino acids. What is DNA? DNA stands for deoxyribonucleic acid. Within the nucleus, chromosomes are found, and these, and their genes are made of DNA. Each chromosome is a very long molecule of tightly coiled DNA. The DNA molecule looks like a twisted ladder, this spiral shape is called a DOUBLE HELIX.

10 Structure of a Nucleotide DNA is a double stranded molecule. The two strands form a helix. It is made up of a backbone of deoxyribose sugar molecules joined to a phosphate group. Below is a diagram of a Nucleotide: The two strands of DNA are joined via bases. There are 4 bases (adenine, thymine, cytosine and guanine). The bases always pair as follows; ADENINE=THYMINE CYTOSINE=GUANINE.

11 Production of Proteins The sequence of bases is called the GENETIC CODE. The sequence of bases on DNA determines the sequence of amino acids in a protein, which then determines the structure and function of a protein. Each amino acid is coded for by 3 bases on the DNA molecule, for example, the mrna strand shown below: Protein synthesis takes place in the cytoplasm on a cell structure called a ribosome.

12 Since the genetic code is held by the DNA contained within the nucleus, a messenger molecule is required to carry the genetic message from the nucleus, to the ribosome. This molecule is called messenger RNA (mrna). The mrna takes a copy of the genetic code from the DNA and carries it to the ribosome, where the protein is assembled from amino acids. Key Area 1.4: Proteins & Enzymes Learning Intentions: 1. Explain the connection between amino acid sequence and protein structure and function. 2. Give the functions of some proteins to include structural, enzymes, hormones, antibodies and receptors. 3. Describe the role of an enzyme and their properties. 4. Give the function of the active site in terms of substrate specificity. 5. Define the term optimum in relation to enzymes. 6. Identify factors that affect enzyme activity such as temperature and ph. 7. Explain why enzymes can be denatured, resulting in a change in their shape, which will affect the rate of reaction. Proteins are required for growth and repair. Proteins are formed from amino acids, and the sequence of amino acids will determine the shape and the function of the protein. Proteins have many functions. Some of these specific types of protein are listed below, along with their functions. Specific Types of Proteins: Hormones - Carry chemical messages in the blood. Enzymes act as biological catalysts to speed up chemical reactions inside cells. Antibodies help to protect the body against infection. Structural give strength and support to cell membranes. Receptors help cells recognize specific substances.

13 What are enzymes? Enzymes are biological catalysts, made by living cells, which speed up the rate of a chemical reaction, without being used up in the process. An enzyme has an active site - a section on the enzyme where a substrate binds to. The shape of this active site is specific and will only bind to one type of substrate. We say that the shape of the active site of an enzyme molecule is complementary to its specific substrate(s). Enzyme + Substrate Products Degradation Reactions (Degrading) Enzyme action results in products. In a degradation reaction, large molecules are broken down to small molecules:

14 Examples of Degradation Reactions Starch + Amylase Maltose (SAM) Hydrogen Peroxide + Catalase Oxygen + Water (HPCOW) Fats + Lipase Protein + Pepsin Glycerol + Fatty Acids (FLGFA) Amino acids (PPA) Synthesising Reactions In some chemical reactions small molecules are built up into large molecules. One example of this is in a plant. Plants take small molecules of glucose-1-phosphate and synthesise these into starch. Glucose-1-phosphate + Phosphorylase Starch Factors affecting the rate of enzyme action Each enzyme is most active in its optimum conditions. If an enzyme is outside the boundary of its optimum conditions, its activity will be slowed or, it may not work at all. Two important factors that can affect enzymes (and other proteins) are: Temperature and ph.

15 Temperature One factor that affects the activity of an enzyme is temperature. The optimum temperature is the temperature where the enzyme works best. Most enzymes have the same optimum temperature of 37 C. 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. The line graph below demonstrates this: ph The second factor that can affect the activity of an enzyme is ph. Different enzymes are most active at different ph values, also called their optimum ph. Many enzymes optimum ph is neutral (ph 7) but not all! There are some enzymes that are most active at different phs. Extremes of ph (strong acid/alkali) can denature the active site of an enzyme, causing the enzyme to become inactive slowing down the rate of reaction, or not working at all.

16 Key area 1.5: Genetic Engineering Learning Intentions: 1. Give the definition of genetic engineering. 2. Identify the stages involved in genetic engineering. 3. The role of Enzymes in genetic engineering. Genetic engineering is the process of transferring genetic information from one cell to another. Genes code for proteins and if transferred into a bacterial cell the bacterial cell will produce that particular protein. The protein can then be removed and purified and used by humans. This is how insulin to treat diabetics is made as the bacteria are able to produce large quantities quickly. The bacteria are said to be genetically modified organisms. 1. Identify section of DNA that contains required gene from source chromosome; 2. Extract required gene; 3. Extract plasmid from bacterial cell; 4. Insert required gene into bacterial plasmid; 5. Insert plasmid into host bacterial cell to produce a genetically modified (GM) organism. 6. Genetically Modified organism produces the required substance (ie. Insulin or Human Growth Hormone). 7. Substance purified for human use.

17 The use of enzymes in Genetic Engineering During the process, certain enzymes are required for genetic engineering to work. The enzyme Endonuclease is used to cut open the DNA molecule, and remove the gene on the chromosome. It is also responsible for opening the plasmid. The enzyme Ligase seals the gene in the plasmid. Key Area 1.5: Respiration Learning Intentions: 1. Identify the source of energy in a cell (Glucose) and the reaction which releases this energy is achieved by a series of enzyme controlled reactions called Respiration. 2. The energy released from the breakdown of glucose is used to generate ATP. 3. State the cellular activities that use energy. 4. Define aerobic respiration and fermentation and state the locations where they occur. 5. Describe the steps involved in aerobic respiration and fermentation in animals and plants. 6. Compare aerobic and anaerobic respiration in terms of energy yield and products in both plant and animal cells. Aerobic respiration is the enzyme-controlled chemical process where glucose is broken down in the presence of oxygen to release energy (ATP) to allow the body to do work and carbon dioxide and water are released as end products. Glucose + oxygen (ATP) energy + CO 2 + H 2 O The energy transferred by ATP can be used for cellular activities such as muscle cell contraction, cell division, protein synthesis and transmission of nerve impulses. Respiration can also take place in the absence of oxygen and is known as the fermentation pathway. In animal cells lactate is produced, and in yeast cells ethanol (alcohol) and carbon dioxide is produced. All of these processes are enzyme controlled and so temperature has an impact.

18 The breakdown of each glucose molecule via the fermentation pathway yields only the initial two molecules of ATP. Word Equations Glucose Carbon Dioxide + Ethanol + energy Glucose Lactate + energy Respiration begins in the cytoplasm. The process of fermentation is completed in the cytoplasm. In Aerobic Respiration, when glucose is broken down to two molecules of Pyruvate, to the production of Carbon dioxide and Water, this part of respiration is completed in the mitochondria. Also, it has been found that the greater number of mitochondria found in a cell, the higher the energy requirement.