DNA Replication, Transcription, & Translation

What was the Griffith experiment?

Showed that harmless R-strain Streptococcus pneumoniae could be transformed into virulent S-strain by a “transforming factor” from heat-killed S-strain bacteria

What was the Griffith role in the discovery of DNA?

Suggests something carried genetic information

What did Oswald Avery contribute to understanding DNA?

Showed that DNA was the “transforming factor” by destroying DNA, RNA, or protein in bacteria.

Give an overview of the Hershey-Chase experiment.

They used T2 bacteriophages to infect bacteria:

• DNA labeled with ³²P (phosphorus)

• Protein labeled with ³⁵S (sulfur)

• Result: Only DNA entered bacteria, proving DNA is the genetic material.

What were the contributions of Watson and Crick?

Discovered the double helix structure of DNA in 1953, explaining how DNA stores and replicates genetic information.

List the 4 nitrogenous bases in RNA and their pairing.

Adenine (A) pairs with Uracil (U), Cytosine (C) pairs with Guanine (G).

Purines in RNA are?

Adenine (A) and Guanine (G).

Pyrimidines in RNA are?

Cytosine (C) and Uracil (U).

What sugar does RNA contain?

Ribose

What is the function of DNA?

Stores genetic information

Where is DNA located?

• Nucleus (eukaryotes)

• Nucleoid (prokaryotes)

What sugar does DNA contain?

Deoxyribose

What is the function of RNA?

Transfers info to make proteins

Where is RNA located?

• Cytoplasm

• Nucleus

What is the central dogma of molecular biology?

DNA → RNA → Protein. (Transcription then Translation)

Why is DNA replication called semi-conservative?

Each new DNA molecule contains one old strand and one new strand as a template.

Name 2 types of bacterial DNA replication.

1. Bidirectional replication – two replication forks
2. Rolling circle replication – used in some bacteriophages and bacterial conjugation

What direction does DNA polymerase III read DNA?

3′ → 5′ (synthesizes new strand 5′ → 3′).

What is the leading strand?

Continuous synthesis toward replication fork

What is the lagging strand?

Discontinuous synthesis forming Okazaki fragments, away from replication fork

What is the function of helicase?

Unwinds DNA

What is the function of primase

Lays down RNA primers

What is the function of DNA polymerase III?

Synthesizes new DNA

What is the function of DNA polymerase I?

Replaces RNA primers with DNA

What is the function of ligase?

Joins Okazaki fragments

What is the function of topoisomerase?

Prevents supercoiling

What are the three types of RNA involved in translation?

1. mRNA

2. tRNA

3. rRNA

What does mRNA do?

Carries codons to ribosomes

What does tRNA do?

Carries anticodon and amino acid

What does rRNA do?

Forms ribosome structure and catalyzes peptide bonds

What are codons?

3-nucelotide sequence on mRNA coding for an amino acid

What are anticodons?

3-nucleotide sequence on tRNA complementary to codon

What are wobbles?

3rd nucleotide of codon can vary without changing amino acid

What is the start codon?

AUG

What were the stop codons?

• UAA

• UAG

• UGA

Where is the promoter?

DNA sequence where RNA polymerase binds

Where is the start codon?

Beginning of coding region on mRNA

What happens at the A site?

Binds incoming tRNA

What happens at the P site?

Holds tRNA with growing peptide chain

Where does transcription happen in eukaryotes?

Nucleus

Where does translation happen in eukaryotes?

Cytoplasm

What is the mRNA in eukaryotes?

Monocistronic

Where does transcription happen in bacteria?

Cytoplasm

Where does translation happen in bacteria?

Cytoplasm

What is the mRNA in bacteria?

Polycistronic