Biology Unit 6: Gene Expression and Regulation

Structure of DNA

Sugar-phosphate backbone linked by covalent bonds. It is double stranded, right handed helix, and has anti-parallel strands that run 5’ to 3’ and 3’ to 5 ‘.

-A pairs with T or U

-C pairs with G

Pyrimidines

One ring-smaller. C, T, U

Purines

Two rings-larger. A, G

Semi conservative Process

One strand of DNA conserved from original parent DNA, one new strand made. Two strands of the parental molecule separate, and each functions as a template for synthesis of a new, complementary strand.

Ligase

Seals the okazaigi fragments together for the lagging strand.

Helicase

Breaks hydrogen bonds between strands of DNA at the replication fork-unwinds DNA.

Topoisomerase

Relieve strain and twisting ahead of the fork by breaking, untwisting, and rejoining.

Primase

Makes primers; initial nucleotide strand, short piece of complementary RNA.

Leading Strand

Made in the same direction as the replication fork moves, DNA polymerase adds nucleotide smoothly, only needs one RNA primer.

Lagging Strand

Made away from the replication fork, okazaki fragments, needs many RNA primers, and fragments are later joined by DNA ligase.

How genetic info is transmitted

1. DNA carries genes

2. Gametes are made by meiosis

3. Fertilization

4. DNA is copied and passed on to offspring

Bacterial Chromosomes

-prokaryotes

-usually one chromosome

-circular DNA
-located in the nucleoid region

-not wrapped around histone proteins

-small

-replication begins at one origin

Eukaryotic Chromosomes

-eukaryotes

-multiple chromosomes

-linear

-inside nucleus

-wrapped around histone proteins

-large

-replication begins at many origins

How DNA packaging affects gene expression

Tightly packed DNA=genes off

-DNA wrapped tightly around histones, form heterochromatin

-Transcription enzymes can’t easily access DNA

Loosely Packed DNA=genes on

-RNA polymerase and transcription factors can bind

Plasmids

Circular, small pieces of DNA. Exist separately from the main chromosome.

-Help bacteria adapt quickly to new environments

-Spread antibiotic resistence between bacteria

-used in genetic engineering as vectors to insert genes

Genetic variation of prokaryotes

-mutations create new alleles

-transcription-bacteria take up free DNA from their environment, incoperate that into the genome

-transduction-DNA is transferred between bacteria by viruses

-conjuction-direct cell to cell contact