Unit 7: DNA Structure & Replication

what biomolecule makes up DNA

nucleotide

parts of nucleotide

sugar, phosphate group, and nitrogenous base

bonds between sugar, phosphate and nitrogenous base

covalent

bonds between nitrogenous bases RNA-RNA

hydrogen bonds

DNA is made up of

2 helix

RNA is made up of

1 helix

Deoxyribonucleic Acid

DNA is a biological molecule that contains instructions for our cells to produce proteins, the building blocks of lifeand is composed of two strands forming a double helix structure.

DNA structure

nucleotides stack

• sugars + phosphates = backbone (sides of ladder)

• basses = rungs of ladder

nitrogenous bases pair with what

their complementary bases through hydrogen bonding

• Thymine, Adenine, Guanine, Cytosine for DNA

• Uracil, Adenine, Guanine, Cytosine for DNA

DNA vs RNA

Single-strand vs double-strand

ribose sugar vs deoxyribose sugar

UAGC vs TAGC

Purine bases

Adenine and Guanine have double ring structure

Pyrimidine bases

Thymine and Cytosine have single ring structure

1 base pair consists of

1 Purine (double ring) + 1 Pyrimidine (single ring)

A + T

G + C

Adenine + Thymine creates

2 hydrogen bonds

Cytosine + Guanine

3 hydrogen bonds

antiparallel

the strands of DNA are flipped/go in opposite directions

• each polynucleotide (strand) has 5’ end and 3’ end

DNA is synthesized from

5’ → 3’

5’ end is

phosphate group

3’ end is

hydroxyl group (on base)

DNA Replication

the process by which a DNA molecule makes a copy of itself on a molecular level from a parent molecule to 2 identical daughters

DNA Replication is

semi-conservative → each new molecule consists of 1 original + 1 newly synthesized strand

• occurs at thousands of places @ the same time

• consists of thousands of replication bubbles

Parental DNA

2 diff strands from which create —> 2 identical molecules form

• 1 half newly synthesized DNA and 1 half original DNA strand

At the center of the replication bubble is

the origin of replication

replication bubble is visible

under microscope

Leading strand

daughter strand that builds from 5’ to 3’ on parental DNA

• creates 3’ → 5’ strand (left to right)

Lagging strand

daughter strand that builds from 3’ to 5’ on parental DNA

• creates 5’ → 3’ strand (left to right)

• one inside of fork (must wait)

• forms via Okazaki fragments

okazaki fragments

Short segments of DNA that are synthesized on the lagging strand so it can go 5’→ 3’

Step 1 of DNA replication is

Unzipping: Helicase enzyme unzips the DNA = REPLICATION FORK

Step 2 of DNA Replication

Stabilizing: Single-strand binding proteins stabilize unwound parent replication fork

(preventing them from re-annealing)

Step 3 of DNA replication

Priming: Primase

• leading strand: Primase binds initial nucleotide base to fork

• lagging strand: primase binds initial nucleotide base to fork for Okazaki fragments

Step 4 of DNA replication

Elongating: DNA Polymerase

• leading strand: DNA Polymerase synthesizes off/elongates primer

• lagging strand: DNA Polymerase synthesizes off/elongates fragment

Step 5 of DNA replication

Replacement of RNA primer w/ DNA: DNA Polymerase

• leading strand: DNA Polymerase replaces

• lagging strand: DNA Polymerase replaces

Step 6 of DNA replication

Joining of fragments: Ligase

• leading strand done

• lagging → ligase connects Okazaki fragments

Proofreading + Correcting DNA

Proofread/correct:

• DNA polymerases proofread newly made DNA, replacing any incorrect nucleotides

• In mismatch repair of DNA, repair enzymes correct errors in base pairing (ex: nuclease)

Repairing DNA

Repair:

• DNA can be damaged by exposure to harmful chemical or physical agents such as cigarette smoke and X-rays; it can also undergo spontaneous changes

• Nucleotide excision repair: nuclease cuts out and replaces damaged stretches of DNA

• The final error rate is only one per billion nucleotides. This makes for about 3 mistakes per cell division in humans.

PCR

replicates a small amount of DNA to a large

• gel confirms PCR