week 3 proteins and enzymes

Question 1

what is the structure of an amino acid

Answer 1

NH2 - CH,R - COOH

• amine group on left
• R is variable side chain
• carboxyl group on right

Question 2

are amino acids chiral

Answer 2

yes all are except glycine

Question 3

what do amino acids behave like

Answer 3

zwitterions

• cations in low pH (positive)
• anions in high pH (negative) (two hydrogens are removed)

Question 4

what are the 7 classes of amino acid

Answer 4

aliphatic 
aromatic
sulphur-containing 
acidic
basic
polar
miscellaneous

Question 5

what is an aliphatic amino acid

Answer 5

R group consists of hydrocarbon chain

e.g. glycine, alanine, valine

Question 6

what is an aromatic amino acid

Answer 6

R group consists of hydrocarbon ring

e.g. phenylalanine, tyrosine, tryptophan

Question 7

what is phenylketonuria (PKU)

Answer 7

patient is unable to metabolise phenylalanine

- build-up causes neurological damage

Question 8

what are sulphur containing amino acids

Answer 8

e. g. cysteine, methionine

- presence of sulphur allows disulphide bridges to form (covalently bonded linkages that occur between two amino acids)

Question 9

what are basic amino acids

Answer 9

e.g. lysine, histidine, arginine

NH2 attached

Question 10

what are acidic amino acids

Answer 10

e. g. aspartate, glutamate

- COO attached

Question 11

what are polar amino acids

Answer 11

e. g. serine, threonine, asparagine, glutamine

- can carry charge at end of R group i.e. -OH

Question 12

what is a miscellaneous amino acid

Answer 12

e.g. proline

Question 13

what is primary structure

Answer 13

sequence of amino acids

• 20^100 possible combinations
• two monomers linked is dipeptide, three is tripeptide, etc. to form polypeptide chain
• monomers linked by peptide bonds

Question 14

what is secondary structure

Answer 14

• the 3D spatial arrangement of amino acids located near each other in the polypeptide chain
• relies on hydrogen bonding
• alpha helix or beta pleated sheet

Question 15

what is tertiary structure

Answer 15

• results when R chain of amino acids in polypeptide interact with each other
• van der waal’s, ionic, hydrogen, disulphide bridges and hydrophobic interactions

Question 16

what structure are functional proteins

Answer 16

• at least tertiary

- some quaternary

Question 17

what is quaternary structure

Answer 17

more than one polypeptide comes together

• all active proteins have at least tertiary structure but they can be modified further and develop quaternary structure
• this is post-translational modification

Question 18

what is denaturation of proteins

Answer 18

• occurs when protein’s chemical bonds are disrupted (possibly destroyed) within its secondary and tertiary structure
• biological functionality is lost
• denaturation is rarely strong enough to break primary structure so that remains the same

Question 19

what are the functions of proteins

Answer 19

1. structural e.g. collagen in cartilage
2. enzymatic
3. receptor proteins
4. hormonal e.g. insulin
5. transport proteins
6. defensive proteins e.g. immunoglobulin
7. storage
8. contractile

Question 20

what are the three types of conjugated proteins

Answer 20

1. glycoproteins
2. lipoproteins
3. metalloproteins

Question 21

what is a glycoprotein

Answer 21

• conjugated protein
• protein with one or more carbohydrate molecule attached
• co-translational/post-translational modification where oligosaccharide (carbohydrate of from 3-6 simple sugars) are attached to protein
• this is glycosylation

Question 22

what are the effects of glycolysation

Answer 22

1. stability
2. solubility
3. cell signalling
4. orientation

Question 23

what are lipoproteins

Answer 23

proteins combined with lipids

Question 24

where are lipoproteins found and what is their function

Answer 24

found in cell membranes

they transport hydrophobic molecules (e.g. cholesterol transport in the blood)

Question 25

what are apolipoproteins

Answer 25

complex of lipoproteins

- they transport fat soluble vitamins and fat soluble hormones around the body

Question 26

what are metalloproteins

Answer 26

protein molecule with metal ion in their structure (co-factor)
- various functions (enzymatic, signal transduction, transport and storage)

Question 27

what are the three types of protein

Answer 27

1. globular
2. fibrous
3. membranous

Question 28

what are globular proteins

Answer 28

functions: storage, enzymes, hormones, transporters, structural
e. g. immunoglobulin

Question 29

what are fibrous proteins

Answer 29

• commonly found in muscle fibres and connective tissue
• elongated shape
• in tissues where tensile strength is required

Question 30

what are membranous proteins

Answer 30

• membrane transporters
• membrane enzymes
• cell adhesion molecules

Question 31

what is an enzyme

Answer 31

a protein molecule that catalyses chemical reactions without itself being destroyed or altered

Question 32

what are the six classes of enzymes

Answer 32

oxireductases - transfer e-
transferases - group transfers
hydrolases - hydrolysis
lyases - form, or add groups to double bonds
isomerases - transfer groups within molecules (form isomers)
ligases - formation of c-c, c-s, c-o and c-n

Question 33

what is a co-factor

Answer 33

non-protein component needed for the reaction

Question 34

what is co-enzyme

Answer 34

heat-stable substance that can aid enzyme reactions

Question 35

what is an isoenzyme

Answer 35

enzymes that catalyse the same reaction but vary in structure and other properties

Question 36

how do enzymes lower activation energy

Answer 36

• entropy reduction (force substrate to be correctly orientated)
• desolvation (weak bonds replace hydrogen bonds)
• induced fit

Question 37

what is Michaelis-menten plot and equation

Answer 37

relates reaction rate (V) to the concentration of the substance

Question 38

what is Vmax

Answer 38

maximum reaction velocity

• tells us how fast a reaction is proceeding when the enzyme is saturated with susbstrate
• high value = fast enzyme

Question 39

what is Km

Answer 39

the substrate concentration when the reaction is at 1/2 the maximum velocity

• low value = good fit
• high value = poor fit

Question 40

what can affect enzyme reactions

Answer 40

• enzyme concentration
• substrate concentration
• temperature
• pH
• inhibitors

Question 41

what happens in competitive inhibition

Answer 41

• an inhibitor binds to the active site
• Vmax unchanged
• Km increases because it takes more substrate to overcome inhibition

Question 42

what is non-competitive inhibition

Answer 42

• an inhibitor binds to a secondary site on the enzyme which changes shape of active site
• Vmax decreased
• Km remains the same

Question 43

why measure enzymes in a clinical setting

Answer 43

• detection of suspected disease
• confirmation of suspected disease and assessing severity
• localisation of disease to organs
• organ pathology
• assessing response to therapy
• organ function
• assessing genetic susceptibility to drug side effects
• inherited metabolic disease
• vitamin deficiencies

Question 44

what factors determine enzyme activity in samples

Answer 44

age, gender, pregnancy, race, time of day, genetics, drugs, disease processes, treatments, hypoxia, cellular damage, physical damage, immune disorders, microbiological agents, genetic defects, nutritional disorders