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Medical Cell Biology and Genetics > Proteins And enzymes > Flashcards

Proteins And enzymes Flashcards

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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
Q

What is activation energy?

A

The minimum energy a substrate requires to allow a reaction

26
Q

What is a transition state?

A

A high energy intermediate between substrate and product

27
Q

Name three things that increase rate of reaction

A

Temperature
Concentration
Enzymes (catalysts)

28
Q

What do enzymes do?

A

Act as biological catalysts - lower activation energy therefore reaction is more likely to occur therefore increased rate.

29
Q

What is Vmax?

A

Maximal velocity of the reaction - when all active sites are saturated with substrate

30
Q

What is Km?

A

Michaelis constant - substrate concentration at half Vmax

31
Q

Low Km means enzyme has _____ affinity for substrate

A

High

32
Q

High Km means enzyme has _____ affinity for substrate

A

Low

33
Q

What is a lineweaver-Burk plot?

A

A reciprocal plot of michealis-menten. Linear plot - easier to estimate Km and Vmax

34
Q

What is the effect of competitive inhibitors on Km and Vmax?

A

Increases Km

Same Vmax

35
Q

What’s the effect of non-competitive inhibitors on Km and Vmax?

A

Same Km

Lower Vmax

36
Q

What are constitutive proteins?

A

Proteins that are constantly produced e.g. Albumin, collagen

37
Q

What type of cells secrete procollagen?

A

Fibroblasts

38
Q

What enzyme produced hydroxyproline?

A

Prolyl hydroxylase (requires vitamin C and iron)

39
Q

What enzyme forms cross links between lysine residues on collagen fibrils?

A

Lysyl oxidase

40
Q

What four things can be used to regulate protein activity in the short term?

A

Substrate/product production
Allosteric regulation
Covalent modification
Proteolytic cleavage

41
Q

What are isoenzymes?

A

Enzymes with the same function but different structures (same substrates, different kinetic/catalytic properties)

42
Q

What do protein kinases do?

A

Transfer phosphate from ATP onto OH of serine, threonine or tyrosine side chains

43
Q

What is the opposite to kinase activity?

A

Phosphatase (require water)

44
Q

Allosteric activators increase the proportion of enzyme in its __________

A

R state - high affinity - more likely to bind substrate

45
Q

Allosteric inhibitors increase the proportion of enzyme in its _______

A

T state - low affinity - less likely to bind substrate

46
Q

Name two allosteric activators of phosphofructokinase

A

AMP

Fructose-2,6-bisphosphate

47
Q

Name two allosteric inhibitors of phosphofructokinase

A

ATP
Citrate
H+

48
Q

ATP is a substrate for phosphofructokinase, how is it an allosteric inhibitor too?

A

When ATP at high concentration, glycolysis needs to be down regulated. Therefore ATP binds at allosteric site to inhibit/slow down reaction.

49
Q

What does rate of phosphorylation/dephosphorylation depend on?

A

ATP concentration

50
Q

What is a zymogen?

A

Inactive form of the enzyme, that’s activates by proteolytic cleavage

51
Q

What enzyme is used to activate chymotrypsinogen (into chymotrypsin)?

A

Trypsin

52
Q

What is the structure of active chymotrypsin?

A

Three chains connected by disulphide bonds

53
Q

What is alpha-1-antitrypsin?

A

An endogenous inhibitor of trypsin - prevents activation cleavage therefore prevents activity

54
Q

What disease is caused by the deficiency of alpha-1-antitrypsin?

A

Emphysema - destruction of alveolar walls by elastase

55
Q

What is a Gla domain?

A

Formed by adding COOH to glutamate residues

56
Q

What is haemophilia A a defect in?

A

Factor VIII (which stimulates activity of factor IX serine protease)

57
Q

What’s the function of protein C?

A

Degrades factors Va and VIII

Medical Cell Biology and Genetics (11 decks)

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