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Science Biology CAT Year 10 - Coggle Diagram
Science Biology CAT Year 10
How it is possible for some genes to code for variations in polypeptides?
A gene can code for variation of polypeptides through gene splicing. There are multiple different ways of gene splicing
Exon Skipping
This is the most common known gene splicing mechanism in which exon(s) are included or excluded from the final gene transcript leading to extended or shortened mRNA variants. The exons are the coding regions of a gene and are responsible for producing proteins that are utilized in various cell types for a number of functions.
Intron Retention
An event in which an intron is retained in the final transcript. In humans 2-5 % of the genes have been reported to retain introns. The gene splicing mechanism retains the non-coding (junk) portions of the gene and leads to a demornity in the protein structure and functionality.
Mutations
Mutations can also cause a variant polypeptide to be produced
This occurs when a rare form base is created and means that the normal base pairings will be changed
This therefore changes what amino acid and protein will be produced at the end
How does one gene codes for one (specific) polypeptide
A polypeptide is coded for through the processes of transcription and translation
The RNA copies a section of the DNA, and then transports it to the the cytoplasm to be "turned" into amino acids
The gene codes for a polypeptide through the help of mRNA and then genetic code. The mRNA takes part of the DNA chain and copies it to be taken into the cytoplasm to be translated by tRNA into amino acids. The genetic code assists this because the various orders of the bases mean that different amino acids can be produced by the same gene.
The genetic codes is also a triplet codon, meaning that each individual code had 3 letter (bases) in it. This creates 64 different ways in which the bases can be ordered, 61 of which code for amino acids and 3 of which are "stop" codes, which stop the extension of the amino acid chain, which subsequently breaks of and folds into a polypeptide
This supports the hypothesis of "One gene codes for one polypeptide", but there are ways in which the gene can be changed to create different amino acids
A polypeptide is another name for a protein
A gene is made up of a long string of DNA, made up of nucleotides of A and T/U and G and C base pairings, a deoxyribose sugar and a phosphate group
Describe the process of protein synthesis (that is, transcription and translation)
Transcription
Transcription is the process in which DNA is copied from a section of DNA to be transferred and used in the cytoplasm for building amino acids and proteins
The transcribed piece of DNA becomes known as messenger RNA (mRNA)
There are 5 stages in DNA transcription
1 - Pre Initiation
RNA polymerase and cofactors (general transcription factors) bind to DNA and unwind it, creating an initiation bubble. This space grants RNA polymerase access to a single strand of the DNA molecule. Approximately 14 base pairs are exposed at a time.
2 - Initiation
The initiation of transcription in bacteria begins with the binding of RNA polymerase to the promoter in DNA. Transcription initiation is more complex in eukaryotes, where a group of proteins called transcription factors mediates the binding of RNA polymerase and the initiation of transcription.
3 - Promoter Clearance
The next step of transcription is called promoter clearance or promoter escape. RNA polymerase must clear the promoter once the first bond has been synthesized. Approximately 23 nucleotides must be synthesized before RNA polymerase loses its tendency to slip away and prematurely release the RNA transcript.
4 - Elongation
One strand of DNA serves as the template for RNA synthesis, but multiple rounds of transcription may occur so that many copies of a gene can be produced.
5 - Termination
Termination results in the release of the newly synthesized mRNA from the elongation complex. In eukaryotes, the termination of transcription involves cleavage of the transcript, followed by a process called polyadenylation. In polyadenylation, a series of adenine residues or poly(A) tail is added to the new 3' end of the messenger RNA strand.
Translation
Translation occurs when the string of mRNA reaches the ribosomes in the cytoplasm
3 leaf clover shaped "things" called transfer RNA (tRNA) bond to 3 bases at a time and form amino acids based on the genetic code
The tRNA keep moving along the chain until a stop code is reached
This causes the amino acid chain to break off and fold into a polypeptide
Underlined Word Definitions
Polypeptide
A polypeptide is defined as a polymer of amino acids joined together by chemical peptide bonds. It is the first stage of a protein
Eukaryote
A eukaryote is an organism consisting of a cell or cells in which the genetic material is DNA in the form of chromosomes contained within a distinct nucleus
Gene
A gene is a unit of heredity which is transferred from a parent to offspring which hold some distinct characteristic.
A gene is a distinct sequence of nucleotides that form a part of a chromosome