1.3 Flashcards
(27 cards)
describe gene expression
•only a fraction of the genes in a cell are expressed as most are ‘switched off’ during differentiation
what does gene expression involve?
•transcription and translation of DNA sequences
what is the first step in protein synthesis?
•transcription
what is transcription?
•when the gene on the DNA strand that codes for a protein is copied into a molecule of mRNA
what is translation?
•takes place in the ribosome when the mRNA code is used to join amino acids together to make a protein
what are the 3 types of RNA?
•messenger RNA (mRNA)
•transfer RNA (tRNA)
•ribosomal RNA (rRNA)
what is RNA?
•ribonucleic acid is a single stranded molecule composed of RNA nucleotides
describe the structure of RNA nucleotides
•ribose sugar
•a phosphate group
•a base (A, U, G or C)
describe the RNA base pair rule
•the base Uracil replaces Thymine and is complementary to Adenine
•A-U
•C-G
what does mRNA do?
•carries the complimentary copy of the DNA code from the nucleus to the ribosome
what happens to mRNA?
•it is transcribed from DNA in the nucleus and translated into proteins by ribosomes in the cytoplasm
what is a codon?
•each triplet of bases on the mRNA molecule which code for a specific amino acid
what does tRNA do?
•each tRNA molecule carries its specific amino acid to the ribosome during translation
whats the special feature of tRNA and what does it do?
•has an anticodon (exposed triplet of bases) at one end and an attachment site for specific amino acid at the other end
why does tRNA fold?
•complementary base pairing
what is the site of translation (protein synthesis)?
•ribosome
what are ribosomes made up of?
•ribosomal RNA and proteins
whats the function of ribosomes?
•to bring tRNA molecules bearing amino acids into contact with mRNA molecule during translation
describe the stages of transcription
•transcription is the synthesis of a molecule of mRNA from a section of DNA by the enzyme RNA polymerase
•RNA polymerase moves along the DNA molecule, unwinding the double helix and breaking the hydrogen bonds between the base pairs, separating the two strands
•RNA polymerase synthesises mRNA using RNA nucleotides and complementary base pairing (A-U C-G)
•when the whole gene is copied, the primary transcript of mRNA has been made
what is RNA splicing?
•RNA splicing is a modification process that the primary transcript of mRNA has to undergo before leaving the nucleus, which creates the mature transcript of mRNA
describe the process of RNA splicing
•the mature transcript will leave the nucleus and go into the cytoplasm where it will meet a ribosome and be translated into a protein
•the introns of the primary transcript are non-coding regions and are removed from the strand during RNA splicing
•the exons are coding regions and are joined together to form the mature transcript of mRNA during RNA splicing
(the order of exons remains unchanged)
describe the process of translation
•tRNA is involved in the translation of mRNA into a polypeptide at a ribosome
•tRNA anticodons bond to mRNA codons by complementary base pairing
•this translates the mRNA genetic code into a sequence of amino acids
•amino acids are held together by peptide bonds
•each tRNA then leaves the ribosome as the polypeptide is formed and is free to pick up another amino acid
what is alternative RNA splicing?
•different proteins can be expressed from one gene as a result of alternative RNA splicing
•different mature mRNA transcripts are produced from the same primary transcript depending on which exons are retained and which introns are removed
what are proteins made up of and how many different types of proteins are there?
•proteins are made up of chains of amino acids of which there are 20 different types
•the length of a protein can vary from many thousands of amino acids to just a few
