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MGD > Session 3 > Flashcards

Session 3 Flashcards

1
Q

How can enzymes be regulated in the long-term?

A

Changes in rate of protein synthesis

Changes in rate if protein degradation

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2
Q

What are isoenzymes?

A

Different forms of the same enzyme with different kinetic properties.

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3
Q

What relationship do Allosteric enzymes show between rate and substrate concentration and why?

A

A sigmoidal relationship: they are multi-subunit enzymes so can exist in a R or T state (binding to one subunit makes it progressively easier to bind to other subunits).

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4
Q

What do Allosteric activators do to target enzymes?

A

Increase the proportion of enzyme in the R state.

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5
Q

What do Allosteric inhibitors do to target enzymes?

A

Increase the proportion of enzyme in the T state.

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6
Q

How is PFK regulated and why is it regulated?

A

Allosterically to set the pace of glycolysis
Activated by fructose-2,6-bisphosphate
Inhibited by ATP, citrate and H+

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7
Q

What is ubiquitination?

A

Covalent modification of protein activity using ubiquitin

Controls cell cycle

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8
Q

Which enzymes are used for phosphorylation and what do they do?

A

Protein kinases.

Transfer the terminal (gamma) phosphate from ATP to an -OH group.

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9
Q

Which enzymes perform de-phosphorylation and what do they do?

A

Protein phosphotases.

Catalyse the hydrolysis removal of phosphoryl groups from proteins.

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10
Q

What do enzyme cascades do?

A

Act to amplify a signal.

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11
Q

What does Proteolytic cleavage achieve? What is it used on?

A

Activates enzymes from their inactive zymogen forms.
May be used to activate digestive enzymes, protein hormones (e.g. insulin), blood clotting, developmental processes and apoptosis.

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12
Q

How is chymotrypsinogen activated?

A

Via Proteolytic cleavage
Forms 3 chains: A chain,B chain and C chain
Controlled by trypsin

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13
Q

How can enzymes be regulated after Proteolytic cleavage?

A

Using inhibitors, they can’t be deactivated back into zymogen form once cleaved.

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14
Q

What is emphysema?

A

Deficiency of alpha1-antitrypsin.

Causes destruction of alveolar walls by elastin.

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15
Q

What is the intrinsic pathway of the blood clotting cascade?

A

Damage to the endothelial lining of blood cells promotes binding of factor 7 to activate the clotting cascade by causing factor 10 activation.
Calcium plays a role.
It is required for sustained thrombin activation.

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16
Q

What is the extrinsic pathway of blood clotting?

A

Trauma releases tissue factor (factor 3) to activate the clotting cascade by causing factor 10 activation.

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17
Q

(Briefly) what occurs in the blood clotting cascade?

A

Factor 10 is activated to factor 10a by the intrinsic or extrinsic pathways.
Factor 10a causes prothrombin to be activated to thrombin.
Thrombin activates fibrinogen to fibrin which forms cross-linked fibrin when factor 13 activates.

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18
Q

What is the structure of prothrombin?

A

Functional part is contained in the C-terminal domain.
Two Kringle domains keep prothrombin in the inactive form.
Gla domains next to the Kringle domains target prothrombin to appropriate sites for activation.

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19
Q

How is prothrombin activated?

A

Activated by calcium ions binding to the calcium-binding region.
Cleaved to release fragment containing the first 3 domains.
Cleaved again to release fully active thrombin: 2 chains (one larger than the other) linked by a Disulphide bond.

20
Q

What are Gla residues (formation and function)?

A

Formed by addition of COOH groups to glutamate residues.
Used in post-translational modification of some factors in the liver and allow interaction with sites of damage and bring together clotting factors.

21
Q

What is the structure of fibrinogen?

A

2 sets of tripeptides (alpha, beta and gamma) joined at N-termini by Disulphide bonds.
3 globular units linked by rods.
N-terminal regions are highly negatively charged and prevent aggregation of fibrinogen,

22
Q

How is a soft fibrin clot formed?

A

Thrombin cleaved peptides A and B from the central globular domain of fibrinogen.
Globular domains on the beta and gamma chains interact with exposed sequences on the N-termini of cleaved beta and alpha chains to form a fibrin mesh (soft clot)
(Like crabs grabbing each others feet with pincers)

23
Q

How is a hard fibrin clot formed?

A

Amine bonds form between side chains of lysine and glutamine residues in different fibrin monomers.
Catalysed by transglutaminase (activated from protransglutaminase by thrombin).

24
Q

What causes classic haemophilia?

A

Defect in factor 8.

Factor 8 stimulates factor 9a.

25
Q

How is haemophilia treated?

A

Using recombinant factor 8.

26
Q

How is the clotting process stopped?

A

Localisation of thrombin: clotting factors diluted and removed by the liver.
Digestion by proteases.

27
Q

How can the blood clotting process be regulated?

A

Using specific inhibitors: antithrombin 3

-Enhanced by heparin binding.

28
Q

How can clots be destroyed?

A

Fibrinolysis

  • Plasminogen activated to plasmin by t-PA or streptokinase
  • Breaks fibrin down into fragments
  • Causes the clot to break down
29
Q

What is heterochromatin?

A

Darker stained DNA in nucleus that is more densely packed and not replicating.

30
Q

What is euchromatin?

A

Lighter stained DNA in the nucleus that is less densely packed as it is replicating.

31
Q

Which groove in a DNA helix is more flexible?

A

The minor groove.

32
Q

How many times in DNA wrapped around a chromatid, what is the DNA-chromatid complex called?

A

Twice.

A nucleosome.

33
Q

What is a histone?

A

An octameric protein used to package DNA by wrapping it around the protein.

34
Q

What structure is formed by many DNA wrapped histones?

A

A solenoid.

35
Q

What is a nucleoside?

A

A pentose sugar attached to a base.

36
Q

What is a nucleotide?

A

A pentose sugar attached to a phosphate group and a base.

37
Q

What is the difference between ribose and deoxyribose sugars?

A

Deoxyribose has an -OH group on C2 replaced with a -H

38
Q

How does DNA bind to a histone?

A

Negative charges on the phosphate group of DNA interact with positive charges on the histone.

39
Q

Which bases are purine?

A

Adenine and guanine.

40
Q

Which bases are pyrimidine?

A

Cytosine, thymine and uracil.

41
Q

How are nucleotides joined in DNA and RNA?

A

Via phosphodiester bonds.

42
Q

Which end of a DNA base is 5’ and which end is 3’?

A

Phosphate end is 5’

Hydroxy end is 3’

43
Q

How many hydrogen bonds form between guanine and cytosine?

A

3.

44
Q

How many hydrogen bonds form between adenine and thymine?

A

2.

45
Q

How can enzymes be regulated in the short-term?

A 
By changes in substrate and product concentration.
By changes in enzyme conformation:
-Allosteric regulation
-Covalent modification
-Proteolytic cleavage

MGD (10 decks)

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