TA Session 1 (2/7)

How many different amino acid side chains are there?

• 10

• 15

• 20

• 25

Answer explanation

There are 20 different amino acids, each with a different side chain.

What kind of bond links amino acids to form proteins?

• Ionic

• Phosphodiester

• Hydrogen

• Peptide

Answer explanation

Peptide bonds form between the alpha carbon of one amino acid and the amino group of the next.

Nucleotides are made up of...

• Nitrogenous base + sugar

• Nitrogenous base + sugar + phosphate

• Sugar + phosphate

Answer explanation

Which of the following has one (1) phosphate group?

• AMP

• ADP

• ATP

• UDP

Answer explanation

AMP stands for adenosine MONOphosphate, so it has one phosphate group.

Pyrimidines have ___ ring(s) and purines have ___ ring(s).

• 2, 1

• 1, 2

• 2, 0

• 0, 1

In DNA, the nucleotide pairs are ...

• A-T and G-C

• A-G and T-C

• A-C and U-G

• A-U and G-C

Gel electrophoresis separates DNA fragments by their ...

• Size

• Charge

• Nucleotide content

Answer explanation

All DNA is negatively charged and travels toward the positive electrode. Smaller fragments are able to travel faster, and end up farther down on the gel.

Heterochromatin is ___, while euchromatin is ___.

• decondensed, highly condensed

• highly condensed, decondensed

• double stranded, single stranded

• single stranded, double stranded

Answer explanation

Heterochromatin is "tightly wrapped" around histones and is less accessible to transcription machinery.

Euchromatin is more "loosely wrapped" and is more accessible ("active").

Which histone modification makes histones more negatively charged, loosening chromatin?

• Methylation

• Acetylation

Answer explanation

Because chromatin is typically basic (+), acetylation makes chromatin more negative (-), decreasing interaction with negatively-charged DNA.

Restriction endonucleases used in molecular biology are...

• Highly specific mammalian enzymes

• Nonspecific mammalian enzymes

• Highly specific bacterial enzymes

• Nonspecific bacterial enzymes

Answer explanation

Restriction endonucleases are bacterial nucleases (DNA-cutting enzymes) that target 4-8 basepair stretches of DNA and are therefore useful in DNA cloning.