Gene Expression

Gene Characteristics

Genes are located in the nucleus along the long

strand of DNA 🡪 chromatin.

Genes are packets of information that contain a

sequence to build protein.

The gene sequence is made up of nitrogen bases.

Once translated the unique nitrogen base

sequence will help produce a specific protein.

This identifies the one gene one protein

hypothesis.

Proteins

Are made up of amino acids.

Amino acids are linked together by peptide

bonds.

Proteins are also called polypeptides.

Proteins are found everywhere in the body:

Enzymes, some hormones, receptor proteins in the

cell membrane, skin, muscle……..

Gene Expression = Protein Synthesis

Gene expression is the process of converting a

gene into a protein.

Protein production is protein synthesis.

Protein Synthesis occurs in the cellular organelle

known as the ribosome.

Ribosomes are located in the cytoplasm and

imbedded in the Rough Endoplasmic Reticulum.

Ribosome

Required for protein

production.

Convert mRNA strands

into polypeptides.

Gene Expression = Protein Synthesis

Referred to as The Central Dogma

Two main stages of gene expression:

Transcription

Takes place in the nucleus.

Translation

Carried out in the ribosome.

Transcription

Is the process of converting DNA into

messenger RNA.

Occurs in the nucleus.

The DNA strand is unzipped and the coding

strand copied.

The blueprint is made by an RNA molecule.

This process ensures the safety of DNA.

DNA never leaves the nucleus to protect the

information carried in the DNA.

Transcription: RNA

RNA (Ribonucleic Acid) Characteristics:

Composed of a single stand.

Contains a ribose sugar. (1 more O2 than DNA)

The RNA stand is composed of nitrogen bases that are

complimentary to a single strand of the DNA molecule.

RNA contains the same nitrogen bases as DNA except

no thymine.

Uracil replaces thymine as the complimentary base pair

of adenine.

Transcription Process

RNA polymerase attached to the site on the DNA that

needs to be transcribed into mRNA.

The RNA polymerase opens the DNA double helix.

As the DNA unzips the RNA polymerase binds to a

promoter region located in front of the gene to be

transcribed.

This sequence tends to be repeated nitrogen base

sequences of adenine and thymine only detected by a

promoter.

Transcription Process Cont..

The RNA polymerase starts to transcribe the DNA

strand from 5’ to 3’.

The DNA strand acts as a template and the mRNA

strand is produced in the same complimentary fashion

as DNA replication.

As the DNA has been transcribed, the DNA will coil

up again.

Once the RNA polymerase reaches the termination

sequence on the DNA it is released and the mRNA

molecule is complete.

Transcription Process Cont…

The mRNA molecule is now free to leave the

nucleus and make its way to the ribosome. 🡪 the

messenger.

RNA polymerase can now be used again to

identify another promoter region to produce

another mRNA molecule.

Translation

Is started when the mRNA strand reaches the

ribosome.

The ribosome attaches to the mRNA strand and

starts to read the strand in sequences of 3

nitrogen bases.

3 nitrogen bases are a codon.

The first codon read is a start codon 🡪 AUG.

The AUG codon attaches to the P site of the

ribosome.

Translation Continued.

As the AUG codon is read, a transfer RNA molecule

carries an amino acid to the P site to start the

polypeptide. (p. 673 Figure 9 (a))

tRNA is a carrier molecule that brings amino acids to

the ribosome.

The tRNA molecule is complimentary to the mRNA

molecule to ensure the correct sequence of amino acids.

tRNA molecules contain an anticodon.

Anticodons are complimentary to codons.

tRNA Molecule

Each amino acid has its

own carrier molecule.

Translation Continued.

As the P site on the ribosome is occupied by the start

codon and first tRNA molecule another tRNA

molecule matches up with the mRNA molecule at the

A site on the ribosome.

The two amino acids are linked together by a peptide

bond.

As the peptide bond is formed, the ribosome moves

along to the next codon.

The A site becomes open and the next tRNA molecule

matches up with the mRNA codon.

Translation Continued…

The ribosome moves along the mRNA molecule

until the whole blueprint is translated.

The end of the mRNA strand is identified by a

unique stop codon. (UAA, UAG, UGA)

There is no tRNA for a stop codon the chain

stops and is released.

A releasing factor protein helps to release the

polypeptide chain from the ribosome.

The 80/20 rule, also known as the Pareto Principle, suggests that roughly 80% of effects come from 20% of the causes. In the context of gene expression and protein synthesis:

  1. Key Concepts: Focus on the critical components:

    • Genes: They contain information to build proteins and consist of sequences of nitrogen bases.

    • Proteins: Made of amino acids linked together and perform essential functions in the body.

    • Gene Expression: The two main steps are transcription (DNA to mRNA) and translation (mRNA to protein).

  2. Transcription will account for about 20% of the total process but is crucial as it ensures the information from DNA is converted to RNA, which is safe within the nucleus.

  3. Translation is where the ribosome reads mRNA to produce proteins. Although it is also fundamental, this is where the majority of protein synthesis activity occurs, potentially representing the remaining 80% of the work done in synthesizing proteins.

By concentrating on understanding these main ideas, you can achieve a comprehensive grasp of gene characteristics and protein synthesis.