Biology Summaries of polypeptide synthesis PDF

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This document contains a summary of information on polypeptide synthesis and contains information of DNA, proteins, peptides and more. Enjoy!...

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Polypeptide Synthesis Overview Genes make proteins or RNA; gene expression. Importance of proteins -

Antibodies, Enzymes, Haemoglobin, Cytochrome C

Definitions Genotype: The gene (Height) Phenotype: What the gene does, affected by genotype and environment (Tall, Short) Eukaryote: Organisms whose cells have a nucleus enclosed within membranes which have no membrane-bound organelles. Prokaryotes: Unicellular organism that lacks a membrane-bound nucleus, mitochondria, or any other membrane-bound organelles. Ribosome: Site for protein synthesis made of rRNA and consists of two subunits. RNA: Ribonucleic acid is a single-stranded molecule with complementary bases. It carries information of amino acid sequence from genes to the ribosomes in the cytoplasm. A single strand of DNA is the blueprint for the mRNA which is transcribed from that DNA strand. Note: T is a U (uracil) and sugar is ribose mRNA (Messenger) Carries transcript from DNA (nucleus) to ribosome in cytoplasm tRNA (Transfer) Contains the anticodon and carries an amino acid (bell shape) rRNA (Ribosomal) Makes up the ribosome RER: Rough Endo

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Transcription: Copying the DNA in the nucleus Translation: From sequences (Bases) to amino acids to polypeptide (form of protein) Polypeptide: Chains of amino acids. Proteins are made up of one or more polypeptide molecules. The amino acids are linked covalently by peptide bonds. Introns: Nucleotide sequence within a gene that is removed by RNA splicing during maturation of the final RNA product. Non - Coding Exons: Any part of a gene that will encode a part of the final mature RNA produced by that gene after introns have been removed by RNA splicing. Coding

Process Transcription: DNA strand is seperated, and mRNA is matched up to the corresponding DNA strand within the nucleus to one gene (Transcribe). mRNA is then spliced, and the non coding bits are removed. It can occur because the bases are complementary (Thymine is replaced by Uracil in mRNA)

Translation: Happens in the ribosome. tRNA begin to match up to the mRNA as it travels through the ribosome in the cytoplasm. The small ribosomal subunit is where the codons attaches and the anticodon on the tRNA matches up. The tRNA, once passed through the ribosome it carries the amino acids and is then reused for the next process. An amino acid sequence is created; polypeptide. The sequence begins to fold in the cytoplasm or organelle where it might be reorganised before being released as a protein. Because mRNA is actually the coded sequence for the mature gene product, and if you compare its triplet codon sequence to the final amino acid sequence of the product protein, you find an exact match. tRNA is simply the vehicle used for linking a given 3 base codon to its appropriate amino acid during a protein synthesis via the anticodon.

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Notes: AUG = Start (Methionine) If there is a mutation that affects these codons, proteins will not be synthesized or will stop at the wrong place in the polypeptide.

Processing Stages The RNA processing of exons

Protein Synthesis 1) 2) 3) 4)

Code for protein is in sequence of bases on DNA Transcription: Codes is copied to pre mRNA as complementary bases Pre-mRNA Spliced to form mRNA Translation: MRna used as a template on a ribosome to add amino acids in the correct order 5) Protein is made

DNA The two strands of DNA are different. Template/Non-coding/Sense Strand: DNA that is transcribed to the mRNA i Non-template/Coding/Antisense Strand: Other strand (Complementary strand of DNA) Code is on the coding strand, so the non coding strand has the template for the mRNA to attach to it.

Degenerate Code The code used to determine the actual order of amino acids is called the degenerate code. There are multiple (64) codons for various amino acids, but there are in fact only 20 amino acids (and three stop codons) used in making proteins. Mutations are errors in the sequence bases of the DNA, this can lead to a different amino acid being made and hence different proteins being produced. (Sickle cell anaemia there is a mutation that codes for valine instead of glutamic acid in one of the Haemoglobin

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polypeptide chains) Silent Mutations: Mutation that result in the same amino acid

Extra Notes There is a promoter prior to the beginning of a gene. Often it is a TATA box which has a base sequence of TATAAA on the DNA strand. RNA polymerase is a key component in the initiation of protein synthesis. This enzyme initiates the separation of the two DNA strands and catalyses the addition of the RNA nucleotides to commence the transcription of the DNA code making and mRNA strand.

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