12 BIO - Gene Expression

what are the steps of transcription

initiation, elongation, and termination

definition of DNA

Dna is a poymer made up of repeating monomer units called nucleotides. it acts as the long term storage and transmisson of genetic information.

definition of RNA

RNA is single stranded ribonucleic acide molecule, its primary function is to generate proteins by copying and carrying genetic codes from DNA

what is transcription

is the first step of gene expression where a single genes DNA is copied into a messenger RNA by the enzyme RNA polymerase inside the nucleus

what is initiation (transcription)

RNA polymerase binds to the promoter sequence initiating gene expression and unwinding the DNA for elongation

what is elongation (transcription)

RNA polymerase build an mRNA strand by attaching RNA nucleotides to the DNA template strand one by one using complementary base pairing (thymine is with uracil)

what is termination (transcription)

RNA polymerase reaches a terminator sequence and both the polymerase and the mRNA detach from the DNA strand. introns are spliced out in a process called RNA splicing leaving the exons to be expressed. a five prime cap and poly a tail are added to the end of the chain to protect the mRNA. mRNA is complete, only one gene long, an exits out the cell via a nuclear pore. DNA then winds back up

what is translation

translation is the cellular process by which the ribosomes move along a single stranded mRNA molecule and read the coded message. this message is used to link amino acids in the correct order to form a polypeptide chain and then a functional protein (eg. an enzyme)

what is a promotor sequence

a specific sequence of DNA bases located just before a gene, it acts as a landing site where proteins like RNA polymerase transcriptions facotrs attach to to start copying DNA into RNA

what is RNA splicing

RNA splicing is a molecular editing process, it removes non coding regions like introns and fuses the remaining coding regions called exons back together allowing the cell to produce correct proteins.

what is the function of the mRNA strand

The function of mRNA is to make sure that the (correct) code / instructions for how to make a polypeptide chain, and therefore protein, reaches the ribosome so that translation can occur. because mRNA is a single stranded molecule it is unstable and easily broken therefore after translation can be broken down by an enzyme

what are triplets

a sequence of three bases along on a DNA molecule called a triplet

what are codons

a sequence of three bases on the mRNA molecule each codon is complementary to a triplet in DNA

what is initiation (translation)

when the mRNA is in the cytoplasm, a ribosome will attach to the start codon (AUG) of the mRNA. the tRNA (transfer RNA) then brings a methionine amino acid.

what is elongation (translation)

the mRNA is read in three bases at a time (codons) the anti codon on the tRNA bonds with its complementary codon on the mRNA and brings with it the correct amino acid, peptide bonds form between the amino acids joining them and the ribosome moves along the rest of the mRNA strand.

what is termination (translation)

the ribosome reaches a stop sequence (UGA, UAG, UAA) and no tRNA matches it so the finished poly peptide chain is released to be folded and modified by the endoplasmic reticulum.

what is a polypeptide chain

a poly peptide chain is a chain of amino acids joined together by peptide bonds

what is a primary structure

sequence of amino acids in it peptide chain

what is a secondary structure

the chain of amino acids will fold into either an alpha helices shape or beta pleated sheets. their shape is maintained by hydrogen bonds between the amino acids

what is a tertiary structure

a tertiary structure is a 3D shape of a single protein molecule or polpypeptide chain. it forms when secondary strucutre like alpha helices and beta pleated sheets fold again (eg, insulin)

what is a quaternary structure

is when several tertiary structures are fitted together (made up of many amino acid chains) eg. haemoglobin

what happens when a protein denatures

it is a chemical process by which a protein loses it shape and therefore its function as a result of an external action. (eg. temp, metals, ph, physical force) the change causes the protein to lose quaternary, tertiary, and secondary structures because the interactions (covalent, ionic, hydrogen, hydrophillic/hydrophobic) have been disrupted

what is degeneracy and redundancy

degeneracy is when more than one codon can code for an amino acid, this therefore means some codons are redundant. ie, if the third base within a codon changes then the amino acid coded for will (usually) not be affected. the bases that are usually common to several codons are the first and second bases and the third base is known as the wobble base. if a code is degenerate a change to the third base through a substitution mutation would not affect the amino acid the codon codes for.

what is a mutation

a mutation is a permanent change in the base sequence of DNA. mutations can be spontaneous meaning the occur during DNA replications or they can be induces caused or induced by a mutagen (eg, radiation)

what is a point mutation

a mutation that occurs within a gene and usually involved the change of one base within the DNA sequence (although can involve whole codons) Point mutations can be base substitution, base insertion, and base deletion

what is a same sense mutation

what is a mis sense mutation

what is a nonsense mutation