Cell Biology

• Nucleus


  Controls cell activities and contain chromosomes, which are made of DNA and contain genetic information (DNA)
• Fungal Cells


  • Fungi are a group of organisms that includes mushrooms, moulds, yeast and toadstools
  • Yeast is a unicellular fungus
  • Yeast cells have a nucleus, cytoplasm and cell wall
  • Yeast has no chloroplasts and so cannot photosynthesise
• Bacterial Cells


  • The DNA in bacteria is not contained in a nucleus, only in chromosomes
  • In addition to this, there are other smaller rings of DNA called plasmids
  • The cell wall is made of cellulose in plant cells but of different materials in fungal and bacterial cells

  
• Cell membrane


  • Controls what molecules enter and leave a cell
  • Consists of phospholipids and proteins and is selectively permeable

  
• Concentration Gradient


  A difference in concentration between two solutions
• Movement of Molecules


  1. Passive transport

  2. Active transport
• Passive transport


  • Occurs down a concentration gradient and does not require energy
  • Examples are diffusion and osmosis
  • Molecules move down the concentration gradient from high concentration to low concentration and stop moving when the two concentrations are equal

  
• Diffusion


  • The movement of molecules in a liquid or gas down a concentration gradient from higher to lower concentration until the molecules are evenly spread out
  • Many substances can enter or leave cells by diffusion
  • Animal cells take in glucose and oxygen for aerobic respiration
  • Carbon dioxide and other waste materials leave animal cells by diffusion
• Osmosis


  The movement of water from a higher water concentration to a lower water concentration through a selectively permeable membrane
• Dilute solution


  High concentration of water, low concentration of solute
• Active Transport


  • Involves movement of molecules and ions against a concentration gradient
  • Requires energy
  • Membrane proteins are involved in this process
• DNA nucleotide


  • The DNA molecule is a double stranded helix
  • There are two strands each of which consists of a backbone with bases attached
  • The bases are joined to each other to form the double helix
• Complementary base pairs


  There are 4 bases called Adenine, Thymine, Cytosine and Guanine
• Genetic Code


  • The genes on a chromosome are made up of a sequence of bases
  • Each different sequence of bases instructs the cell to make a specific protein
  • Proteins are made up of chains of amino acids
  • Three bases in the genetic code will put one particular amino acid into the chain

  
• Protein synthesis


  DNA must stay in the nucleus, so a special molecule called messenger RNA (mRNA) carries a complementary copy of the genetic code from the DNA, in the nucleus to a ribosome, where the protein is assembled from amino acids

  
• Types of proteins


  • Structural
  • Enzyme
  • Hormone
  • Antibodies
  • Receptors
• Enzymes


  • Function as biological catalysts and are made by all living cells
  • They speed up chemical reactions and are unchanged in the process
  • Enzymes have an active site - where the chemical reaction occurs
  • The shape of the active site of enzyme molecules is complementary to a specific substrate(s)
  • Enzyme action results in products
• Types of enzyme reactions

  • Degradation reaction - large molecules broken down into smaller molecules
  • Synthesis reaction - small molecules built up together to make larger molecules
• Degradation reactions


  • Amylase breaks down starch into maltose
  • Catalase breaks down hydrogen peroxide into oxygen and water
• Synthesis reaction


  • Phosphorylase synthesises glucose-1-phosphate into starch
• Factors affecting enzyme activity

  • pH and temperature affect enzyme activity
  • Each enzyme has its own set of optimum conditions
  • If conditions are altered beyond an enzyme's optimum, the shape of the enzyme irreversibly changes (denatured)
  • Enzymes are made of protein, and proteins are denatured at high temperatures (usually above about 60°C)
  • pH also affects the rate of enzyme activity, each enzyme has its own range of pH in which it will work and an optimum pH
• Genetic engineering


  • The transfer of genetic material from one organism to another (e.g. human to bacteria)
  • This process can be used to make the second organism to produce a specific protein
• Plasmid


  • A ring of DNA found in bacteria that is used in genetic engineering
  • Bacteria are often used because their plasmids are easy to remove, alter and replace
• Stages of genetic engineering

  1. Identify section of DNA with required gene

  2. Extract required gene using enzymes

  3. Extract plasmid from bacterial cell

  4. Insert required gene into bacterial plasmid using enzymes

  5. Insert plasmid into host bacterial cell to produce a genetically modified (GM) organism

  6. Grow and culture the bacteria to produce insulin or required product
• ATP


  • A molecule of energy in cells
  • The energy transferred by ATP can be used for muscular contraction, mitosis, active transport, transmission of nerve impulses, and synthesis of proteins
• Aerobic respiration


  • Takes place in the presence of oxygen
  • Glucose is broken down into two molecules of pyruvate, releasing enough energy to yield two molecules of ATP
  • If oxygen is present, each pyruvate is broken down to carbon dioxide and water, releasing enough energy to yield a large number of ATP molecules
• Fermentation


  • A type of respiration that occurs in the cytoplasm in the absence of oxygen
  • In animal cells, the pyruvate molecules are converted to lactate
  • In plant and yeast cells, the pyruvate is converted into ethanol and carbon dioxide
• Comparing respiration and fermentation


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• Other support available for Unit test: Course notes, BBC Bitesize website
• Self-assessment of revision: What areas do I need to work on?