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BISC 312 > Lecture 12 > Flashcards

Lecture 12 Flashcards

1
Q

What is an extremely common strategy to modify enzymes and protein activity?

A

– covalent modifications

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2
Q

T or F, covalent modifications are often reversible and are done by enzymes which are themselves subjected to regulation

A

True

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3
Q

Describe phosphorylation by kinases and dephosphorylation by phosphatases.

A

– utilize an ATP that adds a PO4 to a specific amino acid on an enzyme –> phosphorylation

– dephosphorylation is removal of phosphate by phosphotases

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4
Q

What are zymogens?

A

– inactive forms of enzymes aka proenzymes

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5
Q

How does regulation with zymogens work?

A

– zymogens are activated into enzymes by proteolytic cleavage (protease activation)

– Synthesized in pancreas and secreted into duodenum in small intestine

    • enter as inactive forms and get converted to active proteases in small intestine
    • ensures active enzymes are only in lumen and not in pancreatic cells
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6
Q

T or F, trypsin is a common activator of many zymogens

A

True

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7
Q

What is trypsin?

A

– a common activator of multiple zymogens for enzymes involved in protein degradation and more generally in digestive functions

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8
Q

T or F, zymogens activation by trypsin provides strong and synchronized commitment to digestion of proteins

A

True

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9
Q

Why are good inhibitors needed for trypsin?

A

– because zymogen activation is irreversible, good inhibitors are needed to block key activators such as trypsin

Ex: Pancreatic trypsin inhibitor regulate trypsin activity

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10
Q

How does trypsin active chymotrypsin?

A

– It cleaves at the 15/16 site that results in the formation of the pi chymotrypsin.

– This further cleaves to form a triad by the release of two dipeptides.

– This results in the alpha chymotrypsin, the most active chymotrypsin, and results in a A, B and ,C chain that contain the serine residue, histidine, and Aspartate amino acid.

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11
Q

What are other important biological cascades involving zymogens?

A
    • Blood clotting
    • Caspases: enzymes involved in cell apoptosis
    • Protein hormones: Insulin is derived from pro-insulin
    • Collagen is derived from procollagen
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12
Q

What are the general functions of carbohydrates?

A
    • They act as cellular protection,
    • generate and store biological energy, – serve as molecular recognition analogs, – cell signaling
    • cell adhesion
    • biological lubrication
    • control of protein trafficking, and – maintenance of biological structure.
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13
Q

What is the general molecule formula for carbohydrates?

A

(CH2O)n

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14
Q

T or F, elemental analysis of carbohydrate yield one H2O molecule for every C atom

A

True

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15
Q

T or F, carbohydrates have a very large structural diversity

A

True

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16
Q

What are monosaccharides typically used for?

A

as fuel and as building blocks for synthesis of complex molecules like dna, glycoproteins, storage molecules

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17
Q

What’s the difference between an aldose and ketose sugar?

A

an aldose sugar has a sugar with the 1 carbon containing an aldehyde group. A ketose sugar has a ketone group somewhere along its chain. This ketone group is not carbon 1.

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18
Q

What is the most common form of stereoisomer of sugars in living organisms?

A

D sugars

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19
Q

True or false. Monosaccharides with 3 carbons or more contain 1 or more chiral carbons.

A

True

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20
Q

How do we assign D/L isomers for carbohydrates?

A

– the position of the last chiral carbon from the carbonyl group.

– If the last chiral carbon contains the OH to the right, it is a d sugar.

– If the last chiral carbon contains an OH to the left, it is an L sugar.

21
Q

True or false.

At equilibrium, carbohydrates are typically in their cyclic form

A

True

22
Q

True or false.

Furan are 5-membered sugar sings that result from the 4C alcohol attacking the 1C carbonyl group

A

True

23
Q

True or false?

Pyranose is made from the attack of the C5 sugar on the C1 carbonyl to give a 6 membered sugar ring.

A

True

24
Q

Which carbon in a sugar is considered the anomeric carbon?

A

C1

25
Q

What is an anomeric carbon? How does this relate to sugars?

A

– Carbon that can readily change between different epimers ( molecules that differ only by one stereocenter) by forming the open chain intermediate and form the other epimer.

–If there is a hemiacetal on the sugar ring, it can open and change from the alpha or beta sugar.

26
Q

True or false.

The alpha sugar form has its alcohol in the hemiacetal forming upwards whereas the beta has it pointing downward

A

False. alpha has it pointed downward and the beta is pointed up

27
Q

How can you tell whether an open chain sugar will form an alpha or beta epimer?

A

– If the C1 alcohol in the open chain is on the right, it is alpha.

– If the C1 alcohol is pointing to the left, it is beta

28
Q

What are common derivatives of monosaccharides

A

methylation, acetylation, and phosphorylation

29
Q

What makes a sugar a reducing sugar?

A

having a hemiacetal allows it to be a reducing sugar. This allows it to open and be in a more readily oxidizable form.

*note: reducing sugar loses electrons

30
Q

What does reducing sugar mean?

A

It means it is able of being oxidized and reduce other stuff. It is equivalent to saying it is a reductant.

31
Q

Why can’t an acetal be reducing?

A

It will be locked into its ring conformation, which is oxidizable because it needs to be open in order to be oxidized effectively

32
Q

What are the types of glycosidic bonds?

A

O-glycosidic or N-glycosidic

33
Q

What is the main difference between glycogen and amylopectin?

A

– Glycogen has branching every 10-12 residues

– whereas amylopectin branches every 30 residues.

– Therefore glycogen is more branched.

34
Q

Whats the difference between amylose and amylopectin?

A

amylose has no branching

35
Q

Why are glycogen/amylopectin good storage molecules?

A

Branching allows good storage in a small area, allows for glucose stores to remain inside the cell and not diffuse out since it is good for cell, and it osmotically inactives glucose.

36
Q

Why is cellulose different than Gylcogen?

A

– cellulose has beta 1-4 bonds and is linear in structure. This allows it to have fiber like structures with high intra-fiber hydrogen bonding.

– The glycogen branching of alpha 6 favor packing whereas the beta favor strengthening.

37
Q

What are glycoproteins?

A

proteins modified with carbohydrates by the ER/golgi at specific AA.

38
Q

Which specific AA allow for glycosidation?

A

Asn for N-glycosidic and Ser/Thr for O-glycosidic.

Specifically, for N-glycosylation, you need Asn-X-Ser or Asn-X,Thr where X can’t be proline

39
Q

Which enzyme allows for glycosidation?

A

glycosyltransferase puts a carbohydrate on a protein to make it a glycoprotein.

40
Q

True or False.

O phenotypes have a mutated glycosyltransferase enzyme

A

true

41
Q

What type of glycosyl is transferred via the A type glycosyltransferase?

A

N-acetylgalactosamine

42
Q

What type of glycosyl is transferred by B type?

A

galactose

43
Q

True or false. O blood type makes anti a and B antibodies

A

true

44
Q

What is EPO?

A

– glycoprotein involved in stimulating RBC production through its 3x N-glycosylated asn residues and 1x
O-glycosylated Ser residues.

– This pattern prevents degradation and stimulation of RBC

45
Q

What type of glycosylation patterns do mucins have?

A

Ser/Thr o linked glycosylation

46
Q

What are functions of mucins?

A

cell adhesion, fertilization, barrier to pathogens

47
Q

Why are reducing properties important?

A
    • for forming polysaccharides chains

- - for non specific reaction with other molecules (e.g. glycosylation in aging)

48
Q

How can reducing properties be blocked?

A

– by locking carbohydrates in their cyclic form (e.g. methylation)

49
Q

What is the difference between hemiacetal and acetal linkages?

A
    • hemiacetal can open

- - acetal linkages are locked

BISC 312 (31 decks)

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