bio 105 - translation and gene regulation

What provides the rules how nucleotide sequences are converted into amino acid sequences?

The genetic code

Codons

A three-nucleotide sequence of DNA or mRNA that specifies a particular amino acid or termination signal; the basic unit of the genetic code.

What do start codons define on an mRNA?

The reading frame

Ribosomes are complexes of...

Ribosomal RNAs (rRNAS) and proteins.

Transfer RNA (tRNA)

Adaptors that carry the appropriate amino acids to the ribosome during translation.

Anticodon

group of three bases on a tRNA molecule that are complementary to an mRNA codon

Charged tRNA

a transfer RNA molecule to which the appropriate amino acid has been attached

Ribosome function in translation

Bring mRNAs and charged tRNAs together to catalyze the reactions needed to build a polypeptide.

Sites of a ribosome

A site, P site, E site

initiation (translation)

mRNA, first tRNA and ribosomal subunits assemble

elongation (translation)

A polypeptide is synthesizes starting at the mRNA start codon and ending with the mRNA stop codon.

termination (translation)

The ribosomal complex disassembles when the stop codon is reached, relapsing the completed polypeptide

When does a newly synthesized protein achieve its correct 2' - 4' structure?

During protein folding

Where does translation occur?

On free ribosomes in the cytosol and attached to the ER

Gene regulation

The ability of cells to control their level of gene expression

Why are genes regulated?

To ensure that proteins and produced at the correct time and in the correct amounts. Also, gene regulation saves energy and raw materials by only producing the products that a cell needs to support its physiology.

Only some genes are expressed in each cell, at diff levels, at diff times, which leads to...

Different cells ending up with different protein complements (different proteomes).

Gene expression refers to the pattern of when and where genes are...

"Turned on" or "turned off"

constitutive gene expression

Gene is always expressed (mRNA transcription always occurs). Genes code for products needed for basic life functions, like cellular respiration proteins.