Gene expression
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what is gene expression
the process by which specific genes are activated to produce a protein
what are the two phases of gene expression
transcription and translation
how does RNA differ from DNA
• single stranded • ribose sugar instead of deoxyribose sugar • Uracil instead of thymine
what are the three types of RNA involved in gene expression
• mRNA • tRNA • rRNA
what is the function of mRNA
carries a copy of the gene to be expressed from the nucleus to the ribosome
what is the function of tRNA
• contains an anticodon which bind to an mRNA codon • carries an amino acid at its attachment site which is involved in the formation of the polypeptide
what are codons and anticodon
codon - a triplet of bases which form an amino acid in an mRNA strand anticodon - complementary triplet of bases on the tRNA which bind to the codon
what is the function of rRNA
forms the structure of ribosomes along with proteins
where does protein synthesis take place
ribosomes
what is a gene
a DNA sequence that codes for a protein
what are the coding regions of a gene called
exons
what are the non-coding regions of a gene called
introns
what occurs during transcription
the base sequence of DNA is copied into an mRNA strand
what is the name of the mRNA strand formed by transcription
primary transcript
what has to occur for the primary transcript to become mature transcript
RNA splicing
what is RNA splicing
a process where enzymes remove the introns from the primary transcript and join the remaining exons together to form the mature transcript
where does transcription take place
the nucleus
what is meant by alternative RNA splicing
different introns can be spliced and different exons can remain part of the transcript in order to produce different proteins
what is the benefit of alternative RNA splicing
one gene can produce many different proteins depending on which introns are spliced and which exons are kept
which enzymes adds nucleotides to the mRNA strand to form the primary transcript
RNA polymerase
explain the process of transcription
• RNA polymerase moves along the DNA unwinding the strand • hydrogen bonds break between base pairs • RNA polymerase synthesises the primary transcript of mRNA by complementary base pairing with the DNA strand • primary mRNA transcript spliced to form mature transcript • mature transcript leaves the nucleus and travels to the ribosome
explain the process of translation
• mRNA molecule attaches to a ribosome • tRNA transports amino acids to the ribosome • the anti codons of tRNA form complementary base pairs with the codons of the mRNA • peptide bonds form between the adjacent amino acids to form the polypeptide • tRNA molecules leave the ribosome to collect another specific amino acid
what is present on the mRNA molecule to signal the start and end of translation
a start codon and a stop codon
what determines a proteins function
the structure of the protein ( sequence of amino acids)