1.3 Gene Expression Flashcards
Transcription
Synthesis of mRNA from a section of DNA
Translation
Synthesis of a protein using instructions from mRNA
mRNA
Messenger RNA carries a copy of the DNA code from the nucleus to the ribosome
tRNA
Transfer RNA folds due to the complementary base pairing and each molecule carries its specific amino acid to the ribosome
rRNA
Ribosomal RNA and proteins form the ribosome
DNA structure
Double stranded
Deoxyribose sugar
Cytosine-Guanine
Adenine-Thymine
RNA structure
Single stranded
Ribose sugar
Cytosine-Guanine
Adenine-Uracil
Transcription stages
Occurs in nucleus
RNA polymerase moves along the DNA and unwinds the strand
It breaks the hydrogen bonds between the bases
RNA polymerase synthesises a primary transcript of mRNA from the RNA nucleotides
This forms hydrogen bonds with the exposed DNA strand by complementary base pairing
RNA polymerase continues synthesising the mRNA molecule until a sequence of stop codons is reached
The mRNA strand then separates from the DNA and is called the primary mRNA transcript
Introns are non-coding regions of the primary mRNA transcript and are removed
Exons are coding regions and are spliced to form the mature mRNA transcript
Translation stages
Occurs in ribosome
Mature mRNA transcript attaches to a ribosome in the cytoplasm
Start codon begins protein synthesis
Complementary tRNA anticodons attach to the mRNA strand, bringing a specific amino acid to form the molecule
Peptide bonds form between the amino acids
Each tRNA molecule leaves the ribosome once the amino acids are attached
Ribosome moves along the mRNA molecule and the polypeptide chain gets longer
Stop codon ends the protein synthesis
Alternative RNA splicing
Same gene can be used to make several different proteins by using different regions as introns or exons
Different mature mRNA transcripts can be produced from the same primary mRNA transcript depending on which exons are retained
