GENE EXPRESSION KEY DEFINITIONS

Polymer

Polymer

made up of many nucleotide monomers (mono means one)

Phosphate

forms the backbone of the DNA polymer, linking the nucleotide to neighbouring sugars

A Nucleotide Base

Hold the double helical structure of DNA together. There are different bases A-T and C-G and A-U

Complementary Base Pairs

The rule of base pairing A-T and C-G and A-U

Gene

A length of DNA located on part of a chromosome, which contains specific characteristics and traits of an organism which can be inherited by it's offspring

Triplet

three nucleotides in a molecule of DNA that codes for a specific amino acid.

Codon

three nucleotides on a messenger RNA that codes for specific amino acids in the synthesis of protein molecules.

Transcription

First step of protein synthesis in the nucleus where a mRNA is created using the DNA template strand

Translation

Second step of protein synthesis where the genetic code carried by the mRNA is translated into a polypeptide chain by the ribosome in the cytoplasm

Peptide Bonds

Bonds formed between the amino acids, building a polypeptide chain

Ribosomes

Organelle in the cell which is the site of protein synthesis, it is made of rRNA

Polypeptide Chains

Chains of amino acids

Protein

A molecule made of amino acids. A molecule made up of one or more folded polypeptide chains that has a function

RNA (ribonucleic acid)

Single stranded, has a ribose sugar and the base uracil instead of thymine

Redundancy

The genetic code shows redundancy, meaning that several codons code for the same amino acid (UUA and UUG code for leucine)

Mutation

A permanent change in the DNA base sequence. It can alter the amino acid sequence of the protein.

Spontaneous Mutations

Occurs as a result of failure in the process of DNA replication. Sometimes mutations are reversed by repairing mechanisms (enzymes). Although rare , the rate of these occurring increases as you get older

Induced mutations

Occur as a result of exposure to mutagens. Mutagens in the environment can cause mutations that in turn influence the phenotype and phenotype of an individual.

Mutagen

Agents such as radiation or chemical substances, or chemical substances, that cause genetic mutations.

Base substitution

The replacement of one base by another. These occurrences may not result in changes to the protein formed, due to redundancy or repairing mechanisms. however if a new amino acid is coded for then it will impact on the protein formed.

Base deletion

mutation that results in the deletion of a base, likely to cause a reading frameshift

Frameshift

altering all the triplets that follow the mutation. Caused by insertion or deletion mutations

Base Insertion

mutations that result in the insertion of a base, likely to cause a reading frameshift

Metabolic Pathway

An enzyme controlled reaction, consisting of a series of chemical reactions occurring within a cell that are essential for survival. A principal chemical (substrate) is modified into a product which will become the substrate for another reaction . The process continues until the final product is produced.

Enzyme

A protein catalyst for biochemical reactions

Catalyst

speed up and control the rate of reactions

substrate

The reactant on which an enzyme works.

anticodon

A sequence of three nucleotide bases on a Transfer RNA molecule, corresponding to a complementary codon in messenger RNA.

Primary structure

The first level of protein structure; the specific sequence of amino acids making up a polypeptide chain.

Secondary structure

The second level of protein structure; the primary structure is bent or twisted to form a helix or pleated sheet. The shape is held in place by hydrogen bonds

Tertiary structure

The third level of protein structure; the overall, three-dimensional shape of a polypeptide due to interactions of the amino acids making up the chain.

Quarternary structure

The fourth level of protein structure; the shape resulting from the association of two or more polypeptide subunits.

Active site

a region on an enzyme that binds to a substrate during a reaction.

Denatured

loss of an enzyme's normal shape so that it no longer functions; caused by a less than optimal pH and temperature

mRNA

messenger RNA; type of RNA that carries instructions from DNA in the nucleus to the ribosome

Promoter region on a gene

Turns the gene on or off and signals the start of transciption

Coding region on a gene

part of a gene that contains the coded information for making a polypeptide chain

Terminator region on a gene

signal to stop transcription

tRNA

transfer RNA; type of RNA that carries amino acids to the ribosome

Antiparallel

Two complementary strands of DNA run next to each other in opposite directions

Semi conservative

Two identical DNA molecules result from DNA replication, each having one original strand and one newly created strand

Process of transcription

1. An enzyme (RNA polymerase) separates the DNA strand, exposing the gene / bases / nucleotides.

2. Free RNA nucleotides are match to the exposed bases on the template strand using the base pairing rule, A-U and G-C.

3. Transcription forms a single mRNA strand. It is complete when (RNA polymerase reaches the terminator sequence) mRNA detaches and moves out of the nucleus into the cytoplasm and attaches to a ribosome in preparation for translation.

Process of translation

1)The ribosomes move along the mRNA from the start codon until the stop codons is reached. 2) Each sequence of 3 bases (codon) on the mRNA is read by the ribosome and matched to the complementary unpaired three base sequence (anticodon) on the tRNA. 3) tRNA carries the amino acid to the ribosome and drops it off. 4) The specific amino acid attached to the tRNA is then added (peptide bond forms) to the polypeptide chain being made.

Degeneracy

The genetic code also shows degeneracy. This means codons coding for the same amino acid differ only by a single letter. The variation is often in the third letter (GUU and GUC code for valine)

Point mutation

gene mutation in which a single base in the DNA has been changed