1.6 - 1.9 + 6.9 - 6.10 Proteins, enzymes and digestion Flashcards
What are proteins made of?
Many amino acids forming a polypeptide joined by peptide bonds
Describe the primary structure of a protein
The sequence of amino acids in a polypeptide chain
Describe the secondary structure of a protein
The way a polypeptide chain will naturally fold and coil, held together by hydrogen bonding i.e beta pleated sheets and alpha helixes
Describe the tertiary structure of a protein
Further folding of the secondary structure, held together by; hydrogen bonds, ionic bonds and disulphide bridges
Describe the quaternary structure of a protein
Several different polypeptide chains held together by bonds, may contain non-protein/prosthetic groups
What are the four main functions of proteins?
- Enzymes
- Antibodies
- Transport proteins
- Structural proteins
How do you test for proteins?
Biuret test: 1. Place sample in solution 2. Add biuret reagent 3. Shake Blue = No peptide bonds Purple = Peptide bonds
Explain the induced fit model of enzyme action
- The proximity of the substrate leads to a change in the enzyme
- This forms the functional active site
- As it changes its shape, the enzyme puts a strain on the substrate molecule
- This distorts the substrate bonds and lowers the activation energy
How does temperature affect the rate of enzyme action?
- Rate of reaction increases to the optimum temp as the kinetic energy of the enzyme increases
- Above optimum temp, rate of reaction decreases as enzyme denatures
How does pH affect the rate of enzyme action?
- pH affects enzymes shapes as it can disrupt the bonds in the tertiary structure of the enzyme
- Enzymes have different optimum pH’s
How does enzyme concentration affect the rate of enzyme action?
- As enzyme concentration increases so does the rate of reaction (until there is another limiting factor e.g substrate concentration)
- More active sites for substrates to bind to
How does substrate concentration affect the rate of enzyme action?
- As substrate concentration increases, so too does the rate of reaction
How does a competitive enzyme inhibitor work?
- It has a similar shape to the substrate
- Occupies the active site so fewer enzyme substrate complexes can form
- Usually bind reversibly
- Can be overcome by increasing substrate concentration
How does a non-competitive enzyme inhibitor work?
- Binds to the enzymes allosteric site
- This causes the active site to change shape so enzyme substrate complexes can’t form
- Cannot be overcome by increasing substrate concentration
How can enzyme inhibitors control metabolic pathways?
- The end product can act as inhibitor of an enzyme earlier in the pathway
- Too much product = more inhibition = product decreases
- Too little product = less inhibition = product increases
Describe the function of the mouth as part of the digestive system
- Physical break down by chewing
- Chemical digestion by salivary amylase
Describe the function of the oesophagus as part of the digestive system
- Transports food from mouth to stomach (facilitated by peristalsis)
Describe the function of the stomach as part of the digestive system
- Physical break down by contraction of muscular walls
- Chemical digestion by proteases
- Temporarily stores food
- Contains HCl acid to kill bacteria
Describe the function of the liver as part of the digestive system
- Produces bile containing bile salts for lipid emulsification
- Bile is then stored in gall bladder
Describe the function of the pancreas as part of the digestive system
- Secretes pancreatic juice into the small intestine. This contains proteases, lipase and pancreatice amylase and is alkali.
Describe the function of the large intestine as part of the digestive system
- Absorbs excess water and ions
- Contains gut bacteria
Describe the function of the rectum as part of the digestive system
- Stores faeces before it is egested
Describe the function of villi in the small intestine
- Increases SA for difusion
- Very thin walled to reduce diffusion distance
- Contain muscle so can move, mixing content of the ileum and mainting concentration gradient
- Good blood supply
How are amino acids and monosaccharides absorbed?
Diffusion and co-transport
How are lipids absorbed?
See diagram explanation
