KA 1.3: Gene expression

what does gene expression involve?

• Gene expression involves the transcrption and translation of DNA sequnces

• Only a fraction of the genes in a cell are expressed

Describe RNA?

• RNA is single stranded and is composed of nucleotides

• The nucleotides contain ribose sugar, phosphate and one of four bases, - cytosine, guanine, adenine and uracil

How does RNA differ from DNA?

DNA is double stranded, has deoxyribose sugar and has thymine instead of uracil

What does mRNA do?

• Carries a copy of the DNA code from the nucelus to the ribosome

• mRNA is transcribed from DNA in the nucleus and translated into proteins by ribosomes in the cytoplasm

• Each triplet of bases on the mRNA molecule is called a codon and codes for a specific amino acid

Role of tRNA?

• Folds due to complemetary base pairing

• tRNA molecule has an anticodon (an exposed triplet of bases) at one end and an attachment site for a specific amino acid at the other end

• Each tRNA molecule carries its specific amino acid to the ribosome

Role of ribosmal RNA (rRNA)?

• Combines with proteins to form the ribosome

Decribe process first stage of Gene expression- Transcription

• RNA polymerase moves along DNA unwinding the double helix and breaking the hyrogen binds between the bases

• RNA polymerase synthesises a primary transcript of mRNA from RNA nucleotides by complementary base paring

• RNA polymerase joins the nucleotides together forming primary mRNa

Decribe process of RNA splicing

• RNA splicing forms a mature mRNA transcript

• The introns of the primary transcript are non-coding regions and are removed

• The exons are coding regions and are joined together to form the mature mRNA transcript

• The order of the exons are unchanged during splicing

Describe process of Translation

• tRNA is involved in the translation of mRNA into a polypepptide at a ribosome

• Translation begins at a start codon and ends at a stop codon

• Anticodons bond to codons by complementary base paring, translating thr genetic code into a sequnce of amino acids

• Peptide bonds join the amino acids together

• Each tRNA then leaves the ribosome as the polypetide is formed

What is alternative RNA splicing?

• Different proteins can be expresswd from one gene, as a result of alternatjve RNA splicing

• Different mature mRNA transcripts are produced from the same primary transcript depending on which exons are retained

how are polypeptides formed?

Amino acids are linked by peptide bonds to form polypeptides

How do polypeptides become functional proteins?

Polypetide chains fold to form the three-dimensional shape of a protein, held together by hydrogen bonds and other interaction between individuals amino acids

Why does protein folding matter?

Protiens have a large variety of shapes which determines their functions

What determines an organisms phenotype?

• Phenotype is determined by proteines produced as a result of gene expression

• Enviromental factors also influnce phenotype