Gene Expression Flashcards
What’s involved in gene expression?
Transcription and translation.
Only a fraction of genes in a cell are expressed.
What do transcription and translation involve?
Messenger RNA (mRNA)
Transfer RNA (tRNA)
Ribosomal RNA (rRNA)
What is different between DNA and RNA?
DNA is double stranded whereas RNA is single stranded.
DNA contain deoxyribose sugar whereas RNA contains ribose sugar.
DNA contains the base thymine which is complementary to adenine whereas in RNA uracil is complementary to adenine.
What’s the role of mRNA?
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.
Each triplet of bases on the mRNA molecule is called a codon and codes for a specific amino acid.
What’s the role of tRNA?
tRNA folds due to complementary base pairing.
Each tRNA molecule carries its specific amino acid to the ribosome.
A 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.
What’s the role of rRNA?
rRNA and proteins form the ribosome (site of protein synthesis).
What happens during transcription?
Transcription begins when RNA polymerase moves along DNA unwinding the double helix and breaking the hydrogen bonds between the 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 during 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 transcript. The order of the exons is unchanged during splicing.
What is alternative RNA splicing?
Produce different mature mRNA.
Dependent on what bases are classified as intron/exons.
Creates variety.
What happens during translation?
The mature mRNA transcript attaches to a 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 bonds between amino acids form polypeptides?
Peptide bonds.
What forms the shape of a protein?
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 determines the function of a protein?
Its shape.
