Biology Lesson 11

DNA is made of

nucleotides

Nucleotides are made of

5-carbon sugar, nitrogenous base, and a phosphate group

Carbon 1’ bonds to

the nitrogenous base

Carbon 2’ bonds to

the hydrogen atom in DNA or the hydroxide group in RNA

Carbon 5’ bonds to

the phosphate group of the next nucleotide

Carbon 3’ bonds to

the hydroxyl group of the next nucleotide

Purines

double ringed nitrogenous bases Adenine and Guanine

Pyrimidines

single ringed nitrogenous bases Cytosine and Thymine

Adenine forms ____ with Thymine

2 hydrogen bonds

Guanine forms _____ with Cytosine

3 hydrogen bonds

Nucleotides are connected by ____ bonds

phosphodiester

Phosphodiester bonds from between

the phosphate group of one nucleotide and the hydroxyl group of another

chain of nucleotides are built in _____ direction

5’ to 3’

Chargaff’s rule

the amount of adenine equals thymine and the amount of cytosine equals guanine.

DNA replication is semi-conservative

each new DNA strand consists of one parents or template strand and one daughter strand

Characteristics of Prokaryotic Replication

They have multiple points of origin and termination as well as proceed in BOTH directions around one chromosome

Characteristics of Eukaryotic Replication

They have multiple linear chromosomes

Helicase

unwinds the double helix

DNA gyrase

relieves strain while the double helix is being unwound to prevent supercoiling and damage of the DNA

single-stranded binding proteins

coat the strands of DNA to keep them seperated

DNA replication requirements

template DNA, enzymes, and nucleotides

DNA polymerase III

synthesizes new DNA by pairing complementary nucleotides to the template DNA in the 5’ to 3’ direction to create a daughter strand

DNA polymerase requires ___ to start

RNA primer

Primase

Generates an RNA primer so that DNA polymerase can bind to the strand

Ligase

Seals the nicks in between Okazaki fragments

Okazaki Fragments

Fragments of DNA that have been synthesized on the lagging strand

Beta Clamp

holds DNA polymerase III to the DNA as it moves along the strand

Clamp loader

loads beta clamps onto DNA template strand

RNA primer

short RNA sequences that enable DNA polymerase to bind

Leading strand

synthesizes continuously in the 5’ to 3’ direction

Lagging strand

synthesizes discontinuously in Okazaki fragments in the 5’ to 3’ direction

step 1 of DNA synthesize on the lagging strand

primase synthesizes an RNA primer to begin DNA replication

step 2 of DNA synthesize on the lagging strand

DNA polymerase adds nucleotides to the RNA primer, creating Okazaki fragments

step 3 of DNA synthesize on the lagging strand

DNA polymerase 1 replaces the RNA primer with DNA

step 4 of DNA synthesize on the lagging strand

DNA ligase joins the Okazaki fragments together to form a continuous DNA strand

Telomeres

specialized structures composed of repeated DNA on the ends of eukaryotic chromosomes for protection

Telomerase

an enzyme that contains an RNA template complimentary to the template sequence of the telomere and synthesizes DNA

Shortening problem

a problem that occurs because after the last RNA primer is removed DNA polymerase cannot complete the synthesis of the lagging strand, leading to progressive shortening of chromosomes

Types of DNA alterations

Mistakes/mutations and mutagens (radiation)

DNA polymerase 1

removes RNA primer from Ogazaki fragments on the lagging strand and replaces it with DNA