KA3 gene expression! Flashcards
What does gene expression involve?
the transcription and translation of DNA sequences.
How many genes are expressed?
Only a fraction of the genes in a cell are expressed.
What does transcription and translation include?
mRNA, tRNA and rRNA. (ALL RNA)
Describe RNA
RNA is single stranded and is composed of nucleotides containing Ribose sugar, phosphate
and 1 of 4 bases : Cytosine, Guanine, Adenine and Uracil
Explain mRNA
mRNA) carries a
copy of the DNA code from the
nucleus to the Ribosome.
Each triplet of bases on the mRNA
molecule is called a CODON and
codes for a specific amino acid.
Explain 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.
Explain rRNA
rRNA and Proteins are used to form the Ribosome.
explain TRANSCRIPTION.
RNA Polymerase synthesises a PRIMARY mRNA TRANSCRIPT from RNA Nucleotides by
complimentary base pairing
The enzyme RNA POLYMERASE moves along DNA UNWINDING the double helix and
breaking the hydrogen bonds between the bases.
What is Uracil complimentary to?
ADENINE
Explain RNA splicing
RNA Splicing involves the removal of the NON-CODING INTRONS and joining together
of the CODING regions called EXONS.
The order of Exons is UNCHANGED during Splicing.
Some of the DNA which is transcribed is NON-CODING and therefore these regions known as INTRONS must be removed from the Primary mRNA Transcript.
During RNA splicing?
The order of Exons is UNCHANGED
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 TRANSLATION
tRNA is involved in the translation of mRNA into a Polypeptide at a Ribosome.
Translation begins at a START CODON and ends at a STOP CODON.
Anticodons bond to Codons by complimentary 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.
describe the STRUCTURE OF PROTEINS
Amino Acids are linked by PEPTIDE BONDS to form POLYPEPTIDES.
Polypeptide Chains FOLD to form the 3-D shape of a Protein, held together by
HYDROGEN BONDS and other interactions between individual amino acids.
Proteins have a large variety of shapes which determines their functions
What is a PHENOTYPE determined by?
Phenotype is determined by the proteins produced as the result of Gene Expression.
Environmental factors also influence phenotype.
