Cellular Processes: Protein Production and DNA Replication

Extracellular Environment

Affects Cellular Protein Production

Cell Receptors

Can Detect necessary extracellular molecule (ligands)

Genotype

The genetic consumption of an individual organism

Phenotype

The set of observable characteristics of an individual resulting from the interaction of its genotype with the environment

Prokaryotic Genomes

Size: 130-14,000 kb; Little non coding DNA (less than 15%)

Operon

A cluster of genes transcribed from the same promoter to give a single mRNA carrying multiple coding sequences

Regulons

A collection of operons with a unified biochemical purpose under control of a regulatory protein/regulator.

Starvation regulon

An example of a regulon

Operon vs. Gene

Operon: A cluster of genes that are transcribed together as a single mRNA molecule; Gene: A specific sequence of DNA that encodes for a protein or functional RNA.

Polycistronic

Refers to mRNA that encodes multiple proteins.

Monocistronic

Refers to mRNA that encodes only one protein.

Regulon

A collection of genes or operons that are regulated by the same regulatory protein.

Role of Regulatory Proteins

Can act as activators or repressors; Activators enhance transcription, repressors inhibit transcription.

Transcription

Process where dsDNA is transcribed into ssRNA.

Coding (+) strand

The strand of DNA that has the code for the protein.

Template (-) strand

The strand used by RNA polymerase to copy the code.

Initiating Transcription

RNA polymerase begins at the promoter, has 6 subunits, with the 6th being the sigma factor.

Promoter

Is upstream of genes and contains a conserved -35 sequence.

Transcription Elongation

Synthesis of mRNA in 5' to 3' direction (U not T), no need for primer.

Translation

Protein synthesis from mRNA where 3 ribonucleotides (codon) equal 1 amino acid.

STOP codons

3 different codons that tell ribosome to stop translation.

Start codon

Initiates translation.

Reading frame

Each codon after the start is translated in a systematic fashion until a stop codon.

Ribosome

Subunits associate during initiation of translation and read mRNA from 5' to 3'.

Transfer RNAs (tRNAs)

Bind codons via an anticodon and add the corresponding amino acid to the polypeptide chain.

Replication Steps

Initiation, Elongation, Termination.

Ori-C

Origin of replication.

DnaA

Initiates replication.

DnaB

Helicase that unzips DNA.

DnaC

Helicase loader.

Dna gyrase

Releases pressure on DNA (topoisomerase).

SSB

Single-strand binding protein that blocks reannealing.

DnaG

Primase that adds RNA primers.

Dna Pol III

Synthesizes new DNA 5' > 3'.

DNA ligase

Ligates pieces of DNA together.

Tus

Forms complex with ter site to stop replication.