Chapter 4: Nucleic Acids and Information Flow

Question 1

What is the general structure of proteins in terms of primary, secondary, tertiary, and quaternary structures?

Answer 1

Primary: the sequence of amino acids (polypeptide chain)

Secondary: results from the interactions of nearby amino acids (alpha helix or beta/pleated sheet)

Tertiary: a combination of alpha helixes and beta sheets (3D shape of protein = FUNCTION)

Quaternary: a combination of large tertiary units (ex: hemoglobin)

Question 2

How are amino acids linked? How can this bond be broken?

Answer 2

Peptide Bonds (formed by DEHYDRATION synthesis = losing water to create a covalent bond)

• This bond can be broken by adding water in a process called HYDROLYSIS

Question 3

What are the different molecules used in translation? (in order of when they are used)

Answer 3

Messenger RNA (mRNA)
Aminoacyl tRNA Synthateses
Transfer RNA (tRNA)
Initiation Factors
Elongation Factors
Release Factors
Ribosome (ribosomal RNA + ribosomal proteins)

Question 4

What is the basic structure of a ribosome? Are Prokaryotic or Eukaryotic Ribosomes bigger?

Answer 4

Large Ribosomal Unit
Small Ribosomal Unit
E, P, and A sites

• Eukaryotic Ribosomes are a little bigger

Question 5

Describe basic tRNA structure. What is the difference between “charged” tRNA and “uncharged” tRNA?

Answer 5

STRAND OF RNA that binds to itself creating several loops, including an ANTICODON loop.

“Uncharged” tRNA binds to tRNA Synthetase (emzyme) where it is also bound to a corresponding amino acid. “Charged” tRNA leaves holding onto the amino acid

Question 6

What happens during the initiation, elongation, and termination of translation?

Answer 6

Initiation: the initiator AUG codon is recognized and Met (a specific amino acid) is established as the first amino acid in the new polypeptide chain

Elongation: successive amino acids are added one by one to the growing chain with the help of charged tRNA

Termination: the addition of amino acids stops when it reaches a Stop Codon (UAA, UAG, UGA) and a release factor binds to the tRNA spot so that the completed polypeptide chain can be released from the ribosome

Question 7

What is the difference between eukaryotic protein synthesis and prokaryotic protein synthesis?

Answer 7

Eukaryotic:
- MONOCISTRONIC (only one ribosome per strand of mRNA -> only one amino acid chain is formed at a time)
- Initiation happens only at the 5’ cap; the first AUG is the start codon (just one)

Prokaryotic:
- POLYCISTRONIC (multiple ribosomes per strand of mRNA -> many amino acid chains can be formed at a time)
- Initiation happens at Shine-Dalgarno Sequences (multiple)