KA3 - Gene Expression Flashcards
What is gene expression?
Gene expression involves the transcription and translation of DNA sequences
What is an RNA nucleotide composed of?
A ribose sugar
A phosphate group
One of the 4 bases (adenine, thymine, cytosine, guanine)
What are the 3 types of RNA?
mRNA (messenger RNA)
rRNA (ribosomal RNA)
tRNA (transfer RNA)
What is the function of mRNA?
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 is the function of rRNA?
rRNA, along with proteins forms the ribosome
The ribosome is the site of protein synthesis
Describe the structure of tRNA
tRNA has a folded shape due to complimentary base pairing
The bases of tRNA are held together by weak hydrogen bonds
A tRNA molecule has an anticodon(an exposed triplet of bases) at one end and an attachment side for a specific amino acid at the other end
What is the function of tRNA?
The role of tRNA is to carry its specific amino acid to the ribosome
Define protein synthesis
Protein synthesis is the process by which instructions from DNA sequences are carried to ribosomes and proteins are made.
What is the first stage of protein synthesis?
Transcription
What is transcription?
Transcription is the process by which mRNA is transcribed from DNA
What is the first stage of transcription?
- The enzyme RNA polymerase moves along DNA, unwinding the double helix and breaking the hydrogen bonds between the bases thereby unzipping the double helix
What is the second stage of transcription?
- As RNA polymerase breaks the bonds, it synthesises a primary transcript of mRNA on the DNA template strand using free RNA nucleotides. These RNA nucleotides form hydrogen bonds with the exposed DNA bases by complimentary base pairing
What is the third stage of transcription?
- A primary mRNA transcript is formed
What two components is the primary transcript made of?
Introns and exons
What are introns?
Introns are regions of the primary transcript of mRNA which are non-coding
What are exons?
Exons are coding regions of the primary transcript of mRNA
What happens during splicing?
The introns are removed from the primary transcript
The exons are then joined together to form the mature transcript
What is the mature transcript?
The mature transcript leaves the nucleus through a pore in the nuclear membrane
The mature transcript travels through the cytoplasm to a ribosome for the next stage of protein synthesis
What is the second stage of protein synthesis?
Translation
What is translation?
Translation is the synthesis of a polypeptide chain under the direction of mRNA at the ribosome
What happens during translation?
Translation begins at a start codon and ends at a stop codon
Anti codons 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
tRNA has an anticodon and amino acid attachment side
What can happen as a result of alternative RNA splicing?
Different proteins can be expressed from one gene, as a result of alternative RNA splicing
What happens depending on which exons are retained?
Different mature mRNA transcripts are produced from the same primary transcript depending on which exons are reatined
What are amino acids linked by and what does this form?
Amino acids are linked by peptide bonds to form polypeptides
What do polypeptide chains fold to form?
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 a proteins function?
Proteins have a large variety of shapes which determine their functions
What is phenotype determined by?
Phenotype is determined by the proteins produced as the result of gene expression
