| What does Gene expression involve | the transcription and translation of DNA sequences so that proteins can be made |
| do all of the genes in a cell code for making a protein? | no
only a fraction of the genes in a cell are expressed |
| What three types of ribonucleic acid (RNA) do transcription and translation involve? | messenger RNA (mRNA)
transfer RNA (tRNA)
ribosomal RNA (rRNA) |
| what is RNA | a single stranded molecule composed of RNA nucleotides containing ribose sugar, phosphate and one of four bases, C, G, A, U |
| Name the four bases found on an RNA molecule | adenine
uracil
cytosine
guanine |
| What is the function of mRNA | carries a copy of the DNA code from the nucleus to the ribsome.
it is trascribed from DNA in the nucleus and translated into proteins by ribosomes in the cytoplasm |
| what is each triplet of bases on an mRNA molecule called | a codon
a codon codes for a specific amino acid |
| describe the structure of a tRNA molecule | they fold due to complementary base pairing
they have an anticodon at one end and an amino acid attachment site for a specific amino acid at the other end |
| what is the function of tRNA | they carry their specific amino acid to the ribosome |
| what is an anticodon | an exposed triplet of bases |
| what is the function of rRNA | forms the ribosome alongside proteins |
| what is transcription | the first step in protein synthesis
when information from DNA is copied into an RNA molecule, a processs which takes place in the nucleus |
| describe the transcription process | Transcription begins when RNA polymerase moves along DNA unwinding the double helix and breaking the hydrogen bonds between the bases
free RNA nucleotides are attracted to the exposed DNA bases
RNA polymerase synthesises a primary transcript of mRNA from RNA nucleotides by complementary base pairing.
When the mRNA primary transcript is complete it breaks away from the DNA molecule which rewinds into its double helix again |
| what happens after a eukaryotic cell transcribes a protein coding gene in the nucleus | the primary mRNA transcript is processed by a process called RNA splicing |
| what does RNA splicing form | a mature mRNA transcript |
| what happens during rNA splicing | the introns of the primary transcript are removed as they are non coding regions
the exons are joined together to form the mature transcript as they are coding regions
the order of the exons are unchanged during splicing |
| describe the process of translation | trNA is involved in the translation of mRNA into a polypeptide at a ribosome
tRNA molecules carrying a specific amino acid attached to the amino acid attachment site arrives at the ribosome
translation begins at a start codon and ends at a stop codon
anticodons bond to codons by complementary base pairing, translating the genetic code into a sequence of amino acids
peptide bonds join the amino acids together
Each tRNA then leaves the ribosome as the polypeptide is formed |
| what is meant by gene expression/ genes that are expressed | genes that code for making a protein |
| why can many different proteins be expressed from one gene | as a result of alternative RNA splicing
different mature transcripts can be produced from the same primary transcript depending on which exons are retained |
| how are polypeptides formed from amino acids | by being linked together by peptide bonds |
| how do polypeptides become proteins | polypeptide chains fold to form the three dimensional shape of a protein, held together by hydrogen bonds and other interactions between individual amino acids |
| what does the shape of a protein determine | the function of the protein |
| what is determined by the protein produced as a result of gene expression | phenotype |
| what factors can influence gene expression? | environmental factors |
