Molecular Genetics

DNA Synthesis

The process of creating new DNA strands using existing DNA as a template.

Semiconservative Replication

DNA replication method where each new DNA molecule consists of one strand from the original DNA molecule and one newly synthesized strand.

Helicase

Enzyme that unzips the double-stranded DNA during replication.

Gyrase/Topoisomerase

Enzyme that relieves tension in the DNA double helix caused by helicase's unzipping.

Primase

Enzyme that adds RNA primers to the DNA strands to initiate DNA synthesis.

DNA Polymerase 3

Enzyme that synthesizes DNA continuously towards the replication fork on the leading strand.

DNA Polymerase 1

Enzyme that double-checks and corrects mistakes in DNA replication.

Exonuclease Enzyme

Enzyme that removes incorrect nucleotides from DNA strands.

Primers

Short RNA sequences that act as starting points for DNA synthesis by DNA Polymerase 3.

SSB Proteins

Proteins that prevent reannealing of the DNA strands during replication.

Leading Strand

The DNA strand synthesized continuously in the 5' to 3' direction.

Lagging Strand

The DNA strand synthesized discontinuously in the 3' to 5' direction.

Okazaki Fragments

Short DNA fragments formed on the lagging strand during DNA replication.

Promoter Region

DNA sequence where RNA Polymerase binds to initiate transcription.

RNA Polymerase

Enzyme that synthesizes RNA from a DNA template during transcription.

Coding/Sense Strand

The DNA strand with the same sequence as the mRNA (5' to 3' direction).

Non-Coding/Antisense Strand

The DNA strand complementary to the mRNA sequence (3' to 5' direction).

The nucleotide at the end of one strand of a fragment of double-stranded DNA has a free phosphate attached to the 5’ carbon of its deoxyribose sugar. The complementary nucleotide has ___

b) a hydroxyl group (-OH) attached to the 3' carbon of its deoxyribose sugar

The function of the poly-adenine tail that is added to mRNA in eukaryotic cells is to

a) prevent degradation of the mRNA

An enzyme, which excises a mismatched base in a newly synthesized strand of DNA, is called

d) an exonuclease

When DNA helicase is active, the result is

d) separation of the two strands of the double helix

A section of mRNA 9 codons long would most likely result in the addition of how many amino acids to a

growing polypeptide (the stop codon is absent from the section of mRNA)?

a) 9

RNA polymerase participates in

d) RNA transcription

7. The term gene is defined as of which of the following?

a) the portion of the DNA molecule that codes for a particular polypeptide sequence

The main support to the DNA molecule is provided by two backbones which run along the two sides of the double helix. These backbones consist of

b) phosphates joined by ester links

During DNA replication, the function of RNA primers is to

c) serve as starting points for DNA strand elongation by DNA polymerase III in the 3’- 5’ direction

Which of the following correctly describes the order in which cell components become involved in protein synthesis?

d) RNA polymerase, mRNA, ribosome, tRNA

DNA is stable because hydrogen bonds are formed between

e) purines and pyrimidines

In what order do the following molecules become involved in DNA replication in E. coli?

1. single-stranded binding proteins

2. DNA polymerase III

3. primase

4. helicase

a) 4,1,3,2

A deoxyribose sugar molecule includes

e) 5 carbon atoms and an oxygen atom in a ring.

In DNA, phosphodiester bonds join

e) two sugar molecules

In eukaryotes, introns are removed before mRNA leaves the nucleus because

a) they do not code for protein

DNA acts as a template for transcription. Which of the following statements regarding the DNA of a gene being expressed is true?

b) After unwinding, only one of the DNA strands acts as a template.

The ‘Central Dogma’ states that the flow of genetic information is in the direction

e) DNA, RNA, protein

A piece of double-stranded DNA consisting of 18 nucleotides would likely create a first-formed mRNA transcript having

b) 3 codons

What happens when telomeres become too short?

b) Cell division stops immediately

The type of change in the DNA most likely to be responsible for the difference between the peptides is

a) a frame-shift mutation

• “difference between the peptides” = change in amino acid SEQUENCE