Microbiology Chapter 6 Part One

Single-Stranded Binding Proteins

bind & stabilize single-stranded DNA

Topisomerase

Keeps the spindle spinning so the DNA doesn’t knot and break

DNA Polymerase III

Main enzyme making new bases

1. needs DNA untwisted to replicate

2. can only add nucleotides to existing chains

3. can only add nucleotides in one direction

Leading Strand

The top strand of DNA being replicated

Lagging Strand

The bottom strand being replicated

Central Dogma

DNA - RNA - Proteins

Transcription

Turning DNA into RNA polymerase

3 stages:

1. initiation

2. elongation

3. termination

Initiation (transcription)

RNA synthesizes into RNA polymerase (RNAP)

3 steps:

1. binds to DNA promoter

2. RNAP denatures DNA strands apart

3. assembles RNA

Elongation (transcription)

RNA Polymerase

4 stages:

1. unwinds DNA when moving forward

2. adds nucleotides to the 3' end of already assembled RNA

3. separates DNA from RNA aftermade

4. joins DNA as it moves forward

Termination (transcription)

When the forks meet, they end the region. Stops Transcription

Rho-independent Termination

3 steps:

1. Hairpin forms from RNA folding back on itself

2. stalling—hairpin causes RNAP to pause DNA

3. weak bonds break

Rho-dependent Termination

3 steps:

1. The rho factor binds to a specific binding site on the growing RNA strand.

2. Rho catches up to RNAP

3. Rho reaches RNAP and pulls the RNA transcript and template DNA apart

mRNA

Transcription of structural genes in the DNA. They have codons.

Codons

3 nucleotide “chunks” bound together by tRNA

tRNA

adapter between RNA/DNA and proteins. Has anticodon.

Anticodon

Binds codon on mRNA

rRNA

Ribosomes can be large and small subunits. Drives protein synthesis.

Non-coding RNA

Regulates transcription at different levels.

Operons

Genes working together/made together. They are turned on and off together.

Structural Genes

Parts of an Operon. They encode enzymes.

Promoter

Part of an Operon: It's where RNA polymerase binds (sometimes needs help of an activator)

Operator

Site next to promoter, where regulators bind.

Regulatory Gene

Encodes regulator (maybe near operon or far)

Inducible Operon

Turned on by the substrate of the enzyme or pathway encoded on the operon. Usually off until turned on.

Repressible Operon

Turned off by product of synthesis. When the product is used up, repression is relieved. Usually turned on.

Antiparallel

DNA 5'end & 3’end coenside

Origin

Where replication starts. More efficient with A and T.

Replication Fork

Where the two strands of DNA are being pulled apart.

Helicases

Separate/untwist the helix.

Translation

A critical part of gene expression where the nucleotide sequence of any ribosome.

3 stages:

1. initiation

2. elongation

3. termination

tRNA sites

1. A site (aminoacyl)—accepts amino acids. tRNA enters in successive steps of elongation

2. P site (peptidyl) - protein

3. E-site - exit

Initiation (translation)

The ribosome assembles around the start codon (AUG) on the mRNA, and the first tRNA carrying methionine binds

Elongation Factors (transcription)

1. codon recognition

2. peptide bond formation

3. Translocation

Termination (Translation)

Stop codons: UAA, UGA, UGA (nonsense codons) bind to release factors and break the bonds.

Eukaryotes

• transcription in nucleus—mRNA

• Translation in cytoplasm—ribosomes

• no operons

Introns

sequences not encoding protein (removed)

Exons

encoding regions (proteins)