3. gene expression Flashcards
what is gene expression
gene expression involves the transcription and translation of DNA sequences so that proteins can be made
only a fraction of the genes in a cell are expressed (i.e. code for making a protein)
name the 3 types of RNA used In transcription and translation
- messenger RNA (mRNA)
- transfer RNA (tRNA)
- ribosomal RNA (rRNA)
what is RNA
(ribonucleic acid)
a single stranded. molecule composed of RNA nucleotides containing ribose sugar, phosphate and one of four bases: cytosine, guanine, adenine, uracil
(adenine pairs with uracil)
what is a codon
each triplet of bases on the mRNA molecule
codes for a specific amino acid
describe the role of mRNA in protein synthesis
mRNA carries a copy of the DNA code from the nucleus to the ribosome
mRNA is transcribed from DNA in the nucleus and translated into proteins by ribosomes in the cytoplasm
describe the role of tRNA in protein synthesis
tRNA folds due to complementary base pairing
each tRNA molecule carries its specific amino acid to the ribosome
a tRNA molecule has an anticodon at one end and an attachment site for a specific amino acid at the other end
what is an anticodon
an exposed triplet of bases
describe the role of rRNA in protein synthesis
rRNA and proteins form in the ribosome
what is RNA splicing
RNA splicing forms a mature mRNA transcript (by processing the primary RNA transcript)
describe RNA splicing
introns (non-coding regions) of the primary transcript are removed
exons (coding regions) are joined together to form the mature transcript - the order of exons is unchanged during splicing
describe 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
describe the 3D structure of proteins
amino acids are linked by peptide bonds to form polypeptides.
polypeptide chains fold to form the 3D shape of a protein, held together by hydrogen bonds and other interactions between individual amino acids
describe the 4 stages of transcription
-begins when RNA polymerase moves along DNA unwinding the double helix and breaking hydrogen bonds between the bases
-free RNA nucleotides are attracted to the exposed DNA bases
-RNA polymerase synthesises a primary transcript of mRNA using RNA nucleotides by complementary base pairing (U-A)
-when the primary mRNA transcript is complete it breaks away from the DNA molecule which rewinds into its double helix again
describe the 4 stages of translation
-the mature mRNA transcript attaches to a ribosome
-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 molecule then leaves the ribosome as the polypeptide is formed
