2.3 Proteins Flashcards
Explain the different levels of protein structure
primary structure - sequence of amino acids
secondary structure - α helix coiling or β pleated sheets
tertiary structure - complex 3D folding (caused by hydrogen/disulphide/ionic bonds between R groups)
quaternary structure - multiple tertiary proteins + other nonprotein molecules (modified)
Explain how the structure of a globular protein determines its function and properties + give an example
- spherical shape, hydrophobic groups on inside and hydrophilic groups on outside - therefore soluble
- specific shape for their roles (active sites in enzymes)
e.g. haemoglobin
Explain how the structure of a fibrous protein determines its function and properties + give an example
- long, rope-like fibres (with α helix structure) connected by crosslinks for high tensile strength
- insoluble in water, hydrophobic groups on outside
e.g. collagen
Explain the stages of RNA transcription
- DNA helicase splits strands (breaking H bonds)
- RNA polymerase binds to template strand (antisense strand)
- free RNA nucleotides bond by complementary base pairings
- RNA polymerase forms phosphodiester bonds between nucleotides
- pre-mRNA strand breaks off, and DNA strands re-bond with each other
- pre-mRNA is then spliced, introns cut out and exons kept to form mRNA
Explain the stages of RNA translation
- mRNA strand exits nucleus into cytoplasm
- it attaches to a ribosome, and tRNA molecules with complimentary anticodons to mRNA codons H bond to the mRNA
- each tRNA has a specific amino acid, which are bonded together by the ribosome through peptide links (condensation reactions) to form a polypeptide
- process continues until stop codon
Identify and explain features of genetic code
universal:
- same for all organisms e.g. ACC always codes for threonine
degenerate:
- more than one triplet combination codes for the same amino acid
non-overlapping:
- each triplet only read once
triplet code:
- three bases code for one amino acid
Describe + explain lock and key, and induced fit models
lock and key
- each substrate has a perfect complimentary fit to the enzyme
induced fit
- the enzymes active site can change slightly to allow substrate to bind, and ‘puts pressure on bonds’ to break substrate into products
Explain the effect of increasing substrate/enzyme concentrations on the rate of an enzyme-controlled reaction
as substrate/enzyme increases, rate of reaction also increases as more reactants to collide, up until the other reactants become the limiting factor and there is no more rate increase
Explain how temperature and pH affects rate of reaction
temp:
too low - not enough KE for successful collisions - low rate
optimum temp - more KE so greater fraction of successful collision - peak rate
too high - h bonds in protein break, denaturation, and change in active site - low rate
pH:
too low or too high - conc H+ ions different, affects bonds in protein and causes denaturation - low rate
optimum pH - works the best - peak rate
Explain the lock and key, and induced fit models for enzyme action
Induced fit:
enzyme and substrate form a complex , the structure of the enzyme distorted so
active site of enzyme fits around the substrate
lock and key:
enzymes are completely specific to
substrates they bind to
PRACTICAL:
Explain how you would investigate the effect of changing enzyme concentration on the rate of reaction
IV: enzyme concentration (protease %)
DV: Time taken for enzyme to breakdown substrate (seconds)
CVs: temp (use water bath), volume and conc of substrate
Method:
2 cm3 protease + 2 cm3 milk in cuvette, use colorimeter to record % transmission every 10 seconds for 3 mins
Analysis:
graph and calculate initial rate (tangent at t=0)
Conclusion:
Increase in enzyme concentration leads to increase R of R as more enzyme (more active sites) available for substrate to bind to (line may level off if substrate is limiting)
