35. Proteins and enzymes Flashcards
1
Q
what are proteins?
A
- most important and ubiquitous macromolecules in cell
– all antibodies
– most enzymes and hormones
– connective tissue
– muscle fibrils
– cillia and flagella - almost all cellular functions
2
Q
what is the structure of proteins?
A
- linear polymers of amino acids
– joined in genetically determined sequence - synthesised by ribosomes
– under genetic direction of mRNA - properties depend on:
– composition of AA sequence
– post-translational modifications (folding, subunit joining, glycosylation) a
3
Q
what are amino acids?
A
- 20 standard types of AAs
– 10 considered essential - most proteins contain all 20
– proportions vary
4
Q
what is the basic structure of amino acids?
A
- carboxyl groups
- amino group
- hydrogen atom
- R-group
– organic substituent (side-chain) - all attached to C atom
5
Q
how are amino acids characterised?
A
- chiral molecules
– except glycine (R=H) all have asymmetric C
– exist in 2 stereoisomeric forms (D/L-isomers) - both isomers exist
– L-amino acids incorperated into proteins - characteristic depend on R-group
– range from simple (H)
– to complex aromatic structures
6
Q
what is aspartame?
A
- artificial (non-saccharide) low calorie sweetener
– L-phenylalanyl-L-aspartyl-methyl ester - widely used in soft drinks and confectionary products
- approx. 200x sweeter than sucrose
– only 4 calories/g
7
Q
what is the structure of aspartame?
A
- dipeptide
– composed of 2 amino acids - L-phenylalanine (Phe)
– as methyl ester - L-aspartic acid (Asp)
8
Q
what are the structures and properties of amino acids?
A
- 9 AA’s non polar
– hydrophobic
– no O or N in R-group
– typical interior of protein (3-D structure)
– if protein mainly hydrophobic AA, will seek hydrophobic regions (interior membrane) - 11 hydrophilic
– R-group disticntly polar
– AAs tend to cluster at protein surface
9
Q
what is the peptide bond?
A
- during protein synthesis
– each AA attached to growing chain in condensation reaction
– bond between AA ususally peptide bond - nature of bond gives protein intrinsic diretionality
– N-terminus and C-terminus
10
Q
what is the peptide bond formation?
A
- mRNA and tRNA (genetically encode)
- requires energy to acivate incoming AA
- initial polypeptide not functional protein
– functional protein has unique stable 3-D shape
11
Q
what are the levels of organisation in protein structures?**
A
–
12
Q
what is the primary structure of proteins?
A
- amino acids
– in polypeptide chain - peptide bond
– between each amino acid - sequence of AA
– determined by DNA sequence - not a functioning protein
13
Q
what is the secondary structure of proteins?
A
- hydrogen bonds between AA
- polypeptide chain coils (folds) into
– alpha-helix
– B-sheet
14
Q
what is the tertiary structure of proteins?
A
- 3D folding single polypeptide
- hydrogen bonds
- di-sulfide bonds
- electrostatic interactions
- hydrophobic effect
15
Q
what is the quaternary structure of proteins?
A
- association of two or more polypeptides
– form multimeric protein
16
Q
what is the denaturation fo proteins?
A
- loss of higher order structure
- associated with loss of biological function
– function not associated with first degree structure - caused by exposure to:
– extreme heat
– extreme pH
– certain chemicals - peptide bonds (covalent) unaffected
- depending on severity of denaturant
– protein may/not refold to original conformation
17
Q
how is thermal denaturation applied in industry?
A
- Taq adapted to live at high T
- extract genomic DNA
- isolate portion of DNA from Taq
– that encodes Taq DNA polymerase - insert into E.coli
18
Q
how are proteins secreted?
A
- synthesised with 15-30 peptides at N-terminus
- signal sequence/peptide
– rich in hydrophobic AAs - ribosomes synthesising secretory proteins
– often attached to cell membran - signal sequence cleaved off by signal petidase
– after secretion to produce mature protein
19
Q
what is the protein 3D structure and how is it dictated?
A
- conformation
- dictated by:
– interactions with solvent
– pH and ionic composition of solvent
– sequence of protein (dictated by DNA sequence of gene encoding protein)
20
Q
what are functional proteins?
A
- eg. enzymes
– protein catalysts - highly specific for reaction they catalyse
– and molecules acted upon (substrate) and produced
21
Q
what affects functional proteins?
A
- substrate
- conditions
– pH
– T - inhibitors
- presence/absence of inhibitor or required co-factors
22
Q
what are industrial enzymes?
A
- textile processing
- grain processing
- food processing
- cleaning
- feed enzymes
- diagnostic/pharma
- waste management
- other
23
Q
what are enzymes?
A
- catalysts
- usually proteins
– some ribonucleic acid (RNA) molecules - perform ciritcal lowering of reaction’s activation energy
– amount of energy required for reaction - don’t change reactions delta G value
– don’t affect free energy of reactants/products
– don’t change whether reaction energy is releasing/absorbing overall
24
Q
how do enzymes affect activation energy?
A
- lower Ea
- bind to reactant molecule in such a way that chemical bond-breaking/forming takes plac emore readily
- increase reaction rate
25
Q
how do enzymes work as biocatalysts?
A
- allow reactions to occue at mild conditons
– T for living organisms
– dilute aqueous solutions
– biological pH range
– atmospheric pressure - specificity and selectivity
– stereospecific (act only one stereoisomer of substrate)
– reaction specific (no wasteful bi-products; 100% yield of desired product)
26
Q
what are the different enzyme classifications?**
A
-
27
Q
what are active sites & substrate specificity?
A
- catalyse reaction, enzyme will bind to one/more reactant molecule
– enzyme’s substrates - substrate broken down to multiple products/come together forming larger molecule
– or swap pieces - active site is where sibstrate binds
28
Q
A
