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Gene Expression (DNA vs RNAs (MRNA, tRNA, rRna), Protein Synthesis…
Gene Expression
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Protein Synthesis
Transcription (Initiation): An enzyme RNA polymerase unwinds the section of DNA carrying the desired gene. Only one strand of the DNA (the "template" is recognised and copied
Translation: Is where the code carried on the mRNA is used to create a functional protein. Is able to read the mRNA stand's 'instructions' and make a protein. This means the body reads the mRNA message in groups of three.
Epigenetics
Effects of Light: Light (too much or too little) can alter an organism's phenotype: Plants of the same species will adopt different growth behaviours under different light regimes , may grow abnormally long stems and lack chlorophyll if grown in low light- 'etiolation'. Whereas human skin will go tan/darken over a long period of time
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Metabolic Pathways : A metabolic pathway is a series of enzyme controlled reactions where the product of one chemical reaction is the reactant for the next.
Inborn errors of metabolism: Mutations in enzyme- coding genes will affect their catalytic action, and affect the metabolic pathways. Diseases caused by such mutations are called 'inborn errors of metabolism'
Mutations: A gene mutation is a change in base sequence of a gene (do NOT write “change in genetic code”) resulting in a new allele. This can occur as error during replication (spontaneous) or as a result of a mutagen (induced). They occur randomly, are relatively rare but the majority are harmful. Mutations persist unchanged over successive generations. Mutations occurring in somatic (body) cells can’t be inherited.
Mutagens: Mutagen – a physical or chemical agent e.g. radiation, uv light, toxin, virus that changes organisms DNA - increasing mutation frequency (above natural background level), Mutations alter genotype. Can be a gene mutation (change in BASE sequence of gene – causing a new allele) or a chromosome mutation. In both cases the genotype is changed.
Gene mutations include (1) Base substitution: one base is substituted for a different base E.g. TCA becomes TGA. (2) Frame shifts - base is inserted / deleted, changing reading frame of each triplet code, and altering ‘meaning’ of the bases that follow.
Pleiotropy & PKU
PLU- Phenylketonuria is caused by a gene mutation that affects enzymes within a metabolic paththway- phenylalanie hydroxylse (PAH) normally breaks down phenylalanine, the mutation results in a non-functional enzyme
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RNA PROCESSING: Before the mRNA leaves the nucleus the non-coding introns are removed and the coding exons are joined together. The number of exons joined together and the way they are joined together may not always be the same. This means that the same piece of DNA can code for different polypeptide chains.