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Proteins And enzymes Flashcards

1
Q

Name 6 functions of proteins

A 
Enzymes (catalysts)
Structural support
Immune protection
Receptors
Ligand in signalling
Transporters
Machines (muscle contraction)
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2
Q

What is an amino acid residue?

A

An amino acid in a protein sequence

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3
Q

What does a low pKr value mean?

A

More likely to lose H+ (more acidic)

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4
Q

If pH of solution is less than the pKr of the amino acid side group then it is ____________.

A

Protonated

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5
Q

What is the primary structure of a protein?

A

The linear sequence of amino acids

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6
Q

What is the secondary structure of a protein?

A

The local spatial arrangement of the polypeptide backbone - alpha helices and beta sheets

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7
Q

What is the tertiary structure of a protein?

A

The overall 3D configuration of a protein

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8
Q

Why do peptide bonds exhibit the trans conformation?

A

Because the cis conformation leads to steric clashes due to repelling groups being close together

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9
Q

What is the ioselectric point (pI) of a protein?

A

The pH at which there is no overall net charge (equal number of positive and negative charges)

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10
Q

If the pI of a protein is more than 7 the the protein is _________

A

Basic.

Mainly positively charged amino acids

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11
Q

If the pI is less than 7 then the protein is _________

A

Acidic.

Mainly negatively charged amino acids

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12
Q

If pH of solution is less than pI then the protein is ________

A

Protonated

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13
Q

If the pH of solution is higher than the pI of protein then the protein is _________

A

Deprotonated

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14
Q

What bonds are present in secondary structure?

A

Hydrogen bonds

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15
Q

Which amino acids are (alpha) helix breakers?

A

Proline - As rotation around the N-Ca bond is impossible

Glycine - as the tiny R group supports other conformations

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16
Q

Which amino acids are strong (alpha) helix formers?

A

Small hydrophobic amino acids e.g. Alanine and leucine

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17
Q

Which is weaker - parallel or anti parallel beta sheets?

A

Parallel - as hydrogen bonds at different angles

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18
Q

What role doe fibroid proteins play?

A

Function in support, shape and protection.

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19
Q

What is the repeating sequence in collagen?

A

Gly - X - Y

Where X and Y are often proline and hydroxyproline

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20
Q

Name the 5 bond types seen in tertiary structure if proteins

A 
Disulphide bonds
Electrostatic interactions
Hydrogen bonds
Van der Waals forces
Hydrophobic interactions
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21
Q

Disulphide bonds form between two _______

A

Cysteines

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22
Q

Disulphide bonds can be broken by _____________

A

Reducing agents

Such as beta-mercaptoethanol

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23
Q

What is protein denaturation?

A

Disruption of the normal native functional protein conformation (by breaking bonds/forces that hold it together)

24
Q

Give examples of what can cause protein denaturation:

A

Heat
PH
Detergents/solvents

25
What is activation energy?
The minimum energy a substrate requires to allow a reaction
26
What is a transition state?
A high energy intermediate between substrate and product
27
Name three things that increase rate of reaction
Temperature Concentration Enzymes (catalysts)
28
What do enzymes do?
Act as biological catalysts - lower activation energy therefore reaction is more likely to occur therefore increased rate.
29
What is Vmax?
Maximal velocity of the reaction - when all active sites are saturated with substrate
30
What is Km?
Michaelis constant - substrate concentration at half Vmax
31
Low Km means enzyme has _____ affinity for substrate
High
32
High Km means enzyme has _____ affinity for substrate
Low
33
What is a lineweaver-Burk plot?
A reciprocal plot of michealis-menten. Linear plot - easier to estimate Km and Vmax
34
What is the effect of competitive inhibitors on Km and Vmax?
Increases Km | Same Vmax
35
What's the effect of non-competitive inhibitors on Km and Vmax?
Same Km | Lower Vmax
36
What are constitutive proteins?
Proteins that are constantly produced e.g. Albumin, collagen
37
What type of cells secrete procollagen?
Fibroblasts
38
What enzyme produced hydroxyproline?
Prolyl hydroxylase (requires vitamin C and iron)
39
What enzyme forms cross links between lysine residues on collagen fibrils?
Lysyl oxidase
40
What four things can be used to regulate protein activity in the short term?
Substrate/product production Allosteric regulation Covalent modification Proteolytic cleavage
41
What are isoenzymes?
Enzymes with the same function but different structures (same substrates, different kinetic/catalytic properties)
42
What do protein kinases do?
Transfer phosphate from ATP onto OH of serine, threonine or tyrosine side chains
43
What is the opposite to kinase activity?
Phosphatase (require water)
44
Allosteric activators increase the proportion of enzyme in its __________
R state - high affinity - more likely to bind substrate
45
Allosteric inhibitors increase the proportion of enzyme in its _______
T state - low affinity - less likely to bind substrate
46
Name two allosteric activators of phosphofructokinase
AMP | Fructose-2,6-bisphosphate
47
Name two allosteric inhibitors of phosphofructokinase
ATP Citrate H+
48
ATP is a substrate for phosphofructokinase, how is it an allosteric inhibitor too?
When ATP at high concentration, glycolysis needs to be down regulated. Therefore ATP binds at allosteric site to inhibit/slow down reaction.
49
What does rate of phosphorylation/dephosphorylation depend on?
ATP concentration
50
What is a zymogen?
Inactive form of the enzyme, that's activates by proteolytic cleavage
51
What enzyme is used to activate chymotrypsinogen (into chymotrypsin)?
Trypsin
52
What is the structure of active chymotrypsin?
Three chains connected by disulphide bonds
53
What is alpha-1-antitrypsin?
An endogenous inhibitor of trypsin - prevents activation cleavage therefore prevents activity
54
What disease is caused by the deficiency of alpha-1-antitrypsin?
Emphysema - destruction of alveolar walls by elastase
55
What is a Gla domain?
Formed by adding COOH to glutamate residues
56
What is haemophilia A a defect in?
Factor VIII (which stimulates activity of factor IX serine protease)
57
What's the function of protein C?
Degrades factors Va and VIII

Medical Cell Biology and Genetics (11 decks)

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