Specialization of Proteins I

Question 0

Is a prosthetic group organic or inorganic?

Answer 0

Prosthetic groups are organic molecules.

Question 1

Define reaction specificity

Answer 1

The reaction will only work for a specific reaction

Question 2

Vmax is the maximum possible reaction rate. When does this occur?

Answer 2

When all binding sites are occupied (saturated).

Question 3

Vmax (the max. rxn rate and when all binding sites are occupied) is dependent on what?

Answer 3

Enzyme concentration

Question 4

Doubling the enzyme concentration does what to Vmax?

Answer 4

Doubles Vmax

Question 5

Kcat (the catalytic constant) is the rate at which…

Answer 5

Kcat is the rate at which the enzyme can catalyze the reaction.
It is known as the EFFICIENCY of the reaction

Question 6

What is substrate affinity?

Answer 6

How well the substrate site binds the substrate

Question 7

Km describes substrate affinity. Define what Km is the concentration of.

Answer 7

Km is the concentration of substrate that causes half of the enzymes to be substrate bound and the velocity of the reaction to be 1/2Vmax.

Question 8

Synthesis/Processing of Collagen

What is the first step that causes the formation of mRNA?

Answer 8

The first step in the synthesis of collagen is the TRANSCRIPTION of the preprocollagen gene in the nucleus.

Question 9

Synthesis/Processing of Collagen

After the first step in which preprocollagen is transcribed in the nucleus, forming mRNA, what happens to mRNA?

Answer 9

mRNA travels to a ribosome on the RER where the polypeptide is SYNTHESIZED.

Question 10

Synthesis/Processing of Collagen

After reaching the ribosome of the RER, what happens to the preprocollagen?

Answer 10

The “pre” sequence on the preprocollagen is a peptide that signals for procollagen to be sent through a secretory route. The preprocollagen polypeptide moves into the lumen of the RER and the signal peptide “pre” is removed.

Question 11

Synthesis/Processing of Collagen

After the “pre” peptide is cleaved in the lumen of the RER, what happens to the polypeptide procollagen?

Answer 11

Proline is hydroxylated, via the actions of prolyl hydroxylase and the coenzyme vitamin C (iron also involved). This allows the strand to coil tightly and then form a TRIPLE HELIX with other strands.

Question 12

Proline, along with the coenzymes vitamin C and iron, does what to the procollagen polypeptide?

Answer 12

It causes the strand to coil tightly and form a triple helix with other strands.

Question 13

Synthesis/Processing of Collagen

After hydroxylation of the prolines of the strands via the actions of prolyl hydroxylase and its cofactors, what happens?

Answer 13

Lysine is hydroxylated via the actions of lysyl hydroxylase and the cofactors vitamin C and iron. OH-Lys (hydroxilysyl?) is formed from this reaction. After hydroxylation of lysine, OH-Lys is glycosylated. This is not well-regulated. If the strand stays in the RER too long, too much glycosylation will occur and collagen will lose its tensile strength.

(occurs in the RER)

Question 14

Synthesis/Processing of Collagen

What happens if the collagen strands stay in the lumen of the RER too long?

Answer 14

Too much glycosylation will occur and collagen will lose its tensile strength

Question 15

What is the effect of excess glycosylation of OH-Lys molecules on the collagen strand?

Answer 15

Collagen will lose its tensile strength

Question 16

Synthesis/Processing of Collagen

After glycosylation of OH-Lys, what occurs?

Answer 16

Disulfide bridges are formed (by oxidation of cysteine). This aligns the strand so that the triple helix can form.

Question 17

Synthesis/Processing of Collagen

What is the significance of the oxidation of cysteines?

Answer 17

Disulfide bridges are formed and the strands are ALIGNED allowing for formation of the triple helix.

Question 18

Synthesis/Processing of Collagen

After disulfide bridges are formed (by the oxidation of cysteine) aligning the strands and forming the triple helix, what happens to the procollagen?

Answer 18

Procollagen is moved to the Golgi Body where it is packaged for secretion from the cell.

Question 20

Synthesis/Processing of Collagen

After procollagen is secreted from the cell in vesicles (packaged and sent out by the Golgi body) what happens to the procollagen triple helix?

Answer 20

The cysteine-rich terminal ends of the procollagen are cleaved by proteases called procollagen peptidases.

Question 21

Synthesis/Processing of Collagen

After the cysteine-rich ends are cleaved (outside the cell), the triple helix loses much of its water solubility. As such, the triple helix now does what?

Answer 21

The triple helix, having lost much of its water solubility, has become hydrophobic. The collagen units will clump together spontaneously to form fibrils.

Question 22

Synthesis/Processing of Collagen

The collagen units have now clumped together to form fibrils after becoming hydrophobic due to the cleavage of cysteine-rich ends. What happens to the fibrils?

Answer 22

The fibrils bundle together spontaneously to form collagen fiber.

Question 23

Describe the causes and consequences of Osteogenesis Imperfecta

Answer 23

Cause: mutation on gene COLIA1/COLIA2, which affects the pro-alpha 1 and 2 chains.
The gene sequence is not correct.
The strands are unable to fold correctly and the abnormal collagen is identified and broken down by the cells.
The defects affect Type I collagen, found in skin, bone, tendon, and arterial walls.
This can cause death or be mild, dependent on severity.

Question 24

Describe the causes and consequences of Scurby

Answer 24

Cause: Lack of vitamin C

Vitamin C is a coenzyme for both lysyl hydroxylase and prolyl hydroxylase.
W/o Lysyl hydroxylase, Lys-OH will not form, no need for lysyl oxidase, cross-linking in the fibril will not occur. This causes THIN SKIN, WEAK AND OVERELASTIC AREAS where collagen is used in the body

W/o prolyl hydroxylase, Pro-OH will not form, so strand will not twist tightly into helical form. BLOOD VESSEL STRENGTH IS WEAKENED (classic bleeding gums).
Procollagen will build up in cell and cause cell death, or improperly folded fibrils lead to collagen that is not very strong.

Question 25

Describe the causes and consequences of Ehlers Danlos Syndrome Type V

Answer 25

Cause: deficiency in lysyl oxidase

W/o lysyl oxidase, the collagen fibrils cannot be stabilized through cross-linking. This causes thin skin and arterial walls.

Question 26

Describe the causes and consequences of Ehlers Danlos Syndrome Type VI

Answer 26

Cause: deficiency in lysyl hydroxylase

W/o lysyl hydroxylase, Lys-OH not formed, no glycosylation. Lack of glycosylation may/may not be an issue; it might help secrete procollagen from cell, absence could cause buildup of the protein inside the cell.
Lack of OH-Lys means there is no substrate for lysyl oxidase to act on to form cross-linking to stabilize the fibril, causing issues with HYPERFLEXIBLE JOINTS AND EYE ISSUES

Question 27

Describe the causes and consequences of Ehlers Danlos Syndrome Type VIIB

Answer 27

Cause: defect in N-terminal protease that cleaves the dangling cysteine-rich polypeptides from the end of the trimer

W/o cleaving cysteine ends, trimer is still hydrophilic and will not spontaneously from into a fibril in proper fashion. Impairs collagen function

Question 28

Describe how Advanced Glycosylation End-products (AGEs) are formed

Answer 28

AGEs are formed when exposed to too much sugar in the blood. Glycosylation happens in the presence of high levels of glucose in the blood. A free amine group on a protein (N-terminal or lysine residues) will react with the aldehyde group on glucose. In the short term it is reversible, but if glucose levels remain high, glucose can rearrange and react with another free amine in the protein. This product is the AGE. It is irreversible and exists for the life of the protein. They are very stiff. When they form in blood vessels, in kidney tubules, or in the eyes, they may be associated with complications that we often see with diabetics: cardiovascular disease, retinopathy, renal disease, and cataracts.

Basically, continuously high levels of blood glucose is bad.