Lecture 6

Question 1

Describe the two main modes of protein degradation in the cell, and their main purpose

Answer 1

There are two pathways of protein degradation; the major pathway (90%) is the ATP dependent ubiquitin polymers in the proteasome. Through 3 enzymes the protein will be tagged with either one or a chain of ubiquitin proteins. The protein will then be degraded in the proteosome complex but the ubiquitin can be reused for new proteins. There is also the ATP independent degradation in the lysosome which contains protein degrading enzymes.

Question 2

· Explain what ubiquitin is, and how it gets attached to target proteins

Answer 2

It’s a small TAG peptide. It get’s attatched to proteins by ubiqination which happens in three steps with 3 enzymes.

Question 3

· Describe the basic structure and function of the proteasome

Answer 3

The proteasome is a large protein complex made out of 33 proteins. It’s responsible for protein degradation.

Question 4

· Name the end products of amino acid breakdown (nitrogen group versus carbon skeleton)

Answer 4

The nitroge group is used for amino acids, nucleotides, biological amines or turns into carbomylphostphate to enter the urea cycle. The carbon skeleton can either enter the citric acid cycle to get ATP, become pyruvate or excalacetrate to becom glucose, or acetylCoA to become ketone bodies and fatty acids.

Question 5

· Name the different mechanisms for amino group removal

Answer 5

Transamination rection where the amino group is transferred to a keto acceptor. Removal as ammonia, a four step process.

Question 6

· Name the five key steps of the urea cycle, and where they occur

Answer 6

1)Formation of carbamoyl phosphate in the mitochondrial matrix 2)Formation of citrulline3)Formation of arginosuccinate4)Arginosuccinate is cleaved into fumarate and arginine.5)Arginine is converted into urea and ornithine. Step 1 and 2 occur in the mitochondria matrix, step 3,4, and 5 occur in the cytosol.

Question 7

Describe how glycolysis and the citrate cycle are connected to protein biosynthesis

Answer 7

Amino acids are derived from seven metabolic intermediates in three metabolic processes: Glycolysis, Pentose phosphate pathway, Citrate cycle