GENE EXPRESSION U1 Flashcards
State what is involved in gene expression
Gene expression involves the transcription and translation of DNA sequences. Only a fraction of genes in the cell are expressed.
Name 3 types of RNA and describe an RNA nucleotide
RNA is a single stranded and is composed of RNA nucleotides.
RNA nucleotides consist of a phosphate group, ribose sugar and one of three nitrogenous bases. Adenine, Uracil, Guanine and Cytosine.
(In RNA Adenine complementary base pairs with Uracil as it DOES NOT contain Thymine)
A-U U-A
G-C C-G
The three types of RNA are: -
mRNA
tRNA
rRNA
Describe the structure and function of mRNA and a codon
mRNA carries a complimentary copy of the DNA code from the nucleus to the ribosome. mRNA is transcribed from DNA in the nucleus and translated into proteins in the cytoplasm.
Each triplet of bases on mRNA is known as a codon and codes for 1 specific amino acid.
1 codon (consisting of three bases) = 1 amino acid in a protein.
Describe the structure and function of tRNA
Transfer RNA (tRNA) folds due to complementary base pairing. tRNA also has a triplet of bases exposed known as an anticodon at one end of the tRNA molecule.
At the other end of the tRNA molecule is the specific amino acid attachment site. The tRNA molecule carries its specific amino acid to the ribosome.
State the function of rRNA
rRNA or ribosomal RNA, together with proteins, form the ribosome.
Describe the process of transcription and the role of RNA polymerase in the process
RNA polymerase moves along DNA unwinding the double helix and breaking the hydrogen bonds between bases. RNA polymerase synthesises a primary transcript of mRNA from RNA nucleotides by complementary base paring.
A-U U-A G-C C-G
RNA polymerase can only add nucleotides onto the 3’end.
The mRNA produced is known as the primary transcript.
Describe the role of RNA splicing
During RNA splicing regions known as introns, or non-coding regions, are removed from the primary transcript and the exons or coding regions remain and are spliced together.
The exons when spliced together form a mature (mRNA) transcript. It is important to remember that during the process of splicing the order of the exons remains unchanged.
Describe the process of translation
The mRNA mature transcript leaves the nucleus to the ribosome for the process of translation into a polypeptide.
(A polypeptide chain is a sequence of amino acids that will eventually become part of a functioning protein).
Translation starts at a START codon and ends at a STOP codon. This is very important to ensure the entire polypeptide chain is produced without any amino acids missing.
The ribosome exposes one codon on the mRNA allowing tRNA to bring a specific amino acid to the ribosome. The correct anticodon on the tRNA will complementary base pair with the codon on the mRNA, bringing the correct specific amino acid with it. The ribosome exposes the next codon where another tRNA and its amino acid will complementary base pair with that codon.
Aligning amino acids are joined together by a peptide bond, allowing the tRNA to leave the ribosome as the polypeptide is formed. This happens throughout the length of the mRNA until it reaches a STOP codon.
Describe the process and function of alternative 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.
State how the basic structure of a protein is formed and how phenotypes are determined
Amino acids are bonded together by peptide bonds to form polypeptide chains.
Polypeptide chains fold to form the three-dimensional 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.
Remember that a phenotype is a physical expression of a gene/characteristic. This is determined by the protein produced as a result of gene expression.
