DNA, proteins and proteomes VCE Biology Unit 3. Contents Structure of DNA Protein Synthesis Protein Formation Protein Function Proteome.

DNA, proteins and proteomes

VCE Biology Unit 3

Contents

Structure of DNA Protein Synthesis Protein Formation Protein Function Proteome

Structure of DNA

DNA (Deoxyribonucleic acid) is found in the nucleus of eukaryotic cells and floating freely in the cytosol of prokaryotic cells.

It is the universal code that is at the basis of all life on the planet.

Mitochondria and Chloroplasts also contain DNA.

Structure of DNA

The DNA is organised into strands called chromosomes on which there are segments which code for the production of proteins called genes.

Structure of DNA

DNA is composed of: a nucleotide base (Adenine - A, Guanine –

G – the purines with double ring structures and Thymine - T and Cytosine – C – the pyrimidines with a single ring structure)

A phosphate group A five carbon sugar (phosphate attaches

to 5’ and nucleotide to 1’

The DNA is a double stranded molecule that forms a helical shape due to the complimentary base pairings of G = C and A = T

Structure of RNA

There are a number of ribonucleic acids involved with DNA in protein synthesis.

They are different to DNA: Different sugar group Thymine is replaced by Uracil Single stranded.

Protein Synthesis Commences with

Transcription. This occurs in the nucleus when a section of DNA is unzipped and copied onto mRNA by complimentary base pairing.

Some sections will not code for amino acids and are deleted.

Protein Synthesis The next stage is called

Translation. The mRNA moves to the ribosome and Transfer RNA brings amino acids to the ribosome based on sequence of nucleotides.

Each set of three mRNA nucleotides is read a one time. Three tRNA nucleotides need to match these by complimentary base pairing.

Protein Synthesis

Proteins are formed by the amino acids joining together into a chain.

Protein Synthesis

Genetic Code Pieces of information in the code based on triplets of

nucleotides Code is non-overlapping Code is universal Code is said to be redundant or degenerate as more

than one triplet can code for the same amino acid Code contains instructions to assemble amino acids sub-

units Information is unambiguous Always includes a START and a STOP instruction

Protein formation

Primary Structure As the amino acids are brought to

the ribosomes by tRNA triplets they form long chains. This is described as the primary structure of the protein.

They will undergo modifications that may include the removal of part of the chain (cleaving) or the addition of carbohydrates.

Protein formation

Secondary Structure Hydrogen bonding between adjacent amino

acids in the primary chain cause the chain to either take a pleated or a coiled shape.

Protein formation

Tertiary Structure The secondary protein may

then become folded taking on the tertiary structure of the protein. This is most to likely to occur in the ER and Golgi Bodies of cells.

It is determined by the number and sequence of amino acids in the chain.

Protein formation

Quaternary Structure Many large complex

functional proteins consist of a number of polypeptide chains joined together. When a protein takes on this configuration (eg. Haemoglobin) then it is said to be its quaternary structure.

Protein function

Proteins are critical to the function of the cell: Enzymes – to control cellular processes Structural Support – as fibres in cells Movement – as fibres in cells Transport - as membrane bound proteins and

as molecules to assist in the movement through interstitial fluids

Protein function

Cell Recognition – defending a cell from attack by the immune system.

Signal Transduction – enabling signals within and between cells.

Hormones – to coordinate the functions of organ systems

Defence – via self markers and the many products which protect us from disease.

Proteomes

The proteome is all the proteins that have arisen from the expression of the genes of an individual.

Proteomics refers to the technologies used to study the proteome.

Proteomics has arisen from the Genomics – the study of the genome, and the two areas are closely linked for obvious reasons.

The next area for exploration in physiological genomics which seeks to examine the actual action of proteins on living cells and tissues.