DNA structure and replication (Gen Bio)

Gen bio

What did scientist originally think carried genetic information?

Proteins

Fredrick Griffith discovery

Bacterial transformation

Bacterial transformation

The acquisition of hereditary information that changes bacterial traits

What happened when Griffith mixed heat-killed S bacteria with living R bacteria

Some harmless R bacteria transformed into disease-causing bacteria

What did Avery, McCarthy, and MacLeod discover in 1944

That DNA was the substance responsible for bacterial transformation, building off Griffiths discovery

What is a bacteriophage

A virus that infects bacteria

What did Hershey and Chase demonstrate in 1952

Bacteriophage DNA enters bacteria and carries genetic instructions

In the H&C experiment, what did radioactive sulfur (³⁵S) help scientists track?

The bacteriophage protein coat

In the H&C experiment, what did radioactive phosphorus (³²P) help scientists track?

The bacteriophage DNA

How did Hershey and Chase know DNA entered the bacteria?

Radioactive DNA was found with the bacterial cells after centrifugation

What are Chargaff’s rules?

In double stranded DNA, adenine equals thymine and guanine equals cytosine

What did Rosalind franklins x-ray images help reveal?

DNA’s helical structure and dimensions

Who proposed the DNA double helix model in 1953

James Watson and Francis Crick

What three components make up a DNA nucleotide

A phosphate group, sugar, and nitrogenous base

What forms the outer backbone and DNA

Altering sugar and phosphate groups

Which nitrogenous bases are purines?

Adenine and Guanine. Both have two rings

Which DNA bases are pyrimidines?

Cytosine and Thymine. Both have one ring

Why does a purine pair with a pyrimidine?

To maintain a consistent width in the DNA double helix

What does antiparallel mean in DNA

The two strands run in the opposite direction

5’ →3’ and the other strand is 3’ → 5’

Where is genetic information encoded in DNA

In the order of its nucleotides

What is a template strand?

An existing DNA strand that guides the synthesis of a new complementary strand

Conservative DNA replication

Two original strands stay together, and a completely new DNA molecule forms

Semiconservative DNA replication

Two DNA molecules, each containing one original strand and one newly synthesized strand

Dispersive DNA replication

Each strand contains mixed sections of old and new DNA

How accurate is DNA replication

There is approx. one error/ billion nucleotides

Where does DNA replication begin

Sites called origins of replication

• Two DNA strands are separated, opening up a replication bubble

• Multiple bubbles allow faster replication

• Eukaryotic cells have many origins of replication

• Replication proceeds in both directions until the entire molecule is copied

What is at the end of each replication bubble

A replication fork, a Y-shaped region where new DNA strands are elongating

Helicase

Enzymes that untwist the double helix at the replication forks

Single stranded binding protien

Stabilizes single stranded DNA

Topoisomerase

Corrects overwinding at replication forks by breaking, swiveling and rejoining DNA strands

Primase

Makes short RNA primer, which is a small piece of RNA that gives DNA polymerase a starting point

DNA polymerase

Reads original DNA strand and adds complementary pair base nucleotides

Cannot build a new strand from scratch

Only adds to the 3’ end

DNA Ligase

Joins DNA fragment together

Nucleotide triphosphate

The building blocks used to make DNA carry the energy needed to connect

Leading strand

Built toward the advancing replication fork

Synthesized continually

No Okazaki fragments

Lagging strand

Built away from advancing fork

Synthesized in short sections

Contains Okazaki fragments

Okazaki fragements

Short sections of DNA made on the lagging DNA strand

DNA polymerase I

Replaces RNA primers with DNA

Repair enzymes

Corrects error and damages

Three ways cells deal with errors/damages

Proof reading - DNA polymerase checks newly added nucleotides and corrects mismatches

Mismatch repair - Repair enzymes correct incorrect base pairings that escaped proof reading

Nucleotide excision repair - Damaged DNA sections are removed and replaced