Protein Synthesis How cells follow DNA directions on

Protein Synthesis How cells follow DNA directions on how to make proteins

DNA = the directions in code �Each chain of nucleotides is a line of code �Each chain contains directions for making many different proteins �Each set of directions is �a gene � 1 gene = 1 protein =1 trait

Steps in making a protein � 1) Copy the Directions for one protein onto RNA � (one gene) � Transcription � 2) Use the RNA directions to make a protein � Translation

1) Transcription �A) RNA polymerase scans the DNA to find the gene it needs to copy �B) RNA polymerase has 4 jobs � 1) unwind the DNA double helix � 2) breaks hydrogen bonds to separate chains � 3) match RNA nucleotides to the DNA gene � 4) fuse the RNA nucleotides together to make a chain of RNA �http: //www. youtube. com/watch? v=zt. Pkv 7 wc 3 y. U& feature=related �http: //www. youtube. com/watch? v=5 Mf. SYn. It. Yvg& feature=related

�The chain of RNA that is made is called m. RNA �Or messenger RNA

�Messenger RNA Carries coded directions out into the cell. �Where m. RNA binds to a ribosome.

2) Translation �A) Translates nucleotide code of RNA into � the amino acid code of a protein �B) Takes place in the cytoplasm �C) Is done by a ribosome �http: //www. biostudio. com/demo_freeman_ protein_synthesis. htm

m. RNA = chain of nuclotides that make up the coded directions for making the protein � Every 3 nuclotides of m. RNA is a codon � Each codon is the code for 1 amino acid

Ribosomes �Made of 2 subunits. �Subunits bind onto m. RNA chain at start codon � 3 codons at a time are inside the ribosome �E is for Exit �Codons in P and A sites are the ones being read

t. RNA �bring amino acids to the ribosome �Match the correct amino acid in place by matching their anti-codon to the m. RNA codon �Fit into the E, P and A sites

t. RNA �Each t. RNA only picks up ONE kind of amino acid �t. RNA drops off amino acids at the ribosome then moves back into the cytoplasm to pick up another amino acid(but always the same kind) � aminoacyl-t. RNA synthetase enzymes bind aa to

Steps to Translation �A) Initiaion � 1) Ribosome subunits bond to m. RNA � 2) t. RNA that matches start codon binds at site P

�B) Elongation � 3) t. RNA that matches 2 nd codon binds at site A � 4) ribosome attaches the 2 amino acids those t. RNAs carry to each other by a � peptide bond � http: //www. phschool. com/science/biology_place/biocoach/translation/elong 1. html

wobble effect �The last base in the anti-codon has some flexibility in what it binds to (wobble room) �So anticodon AGU could bind to UCA or UCG

� 5) Ribosome moves down m. RNA chain by � one codon � 6) the first t. RNA �Moves into the E �site and exits �the ribosome

� 7) the next t. RNA moves into place

Termination � 8) Ribosome moves down m. RNA to stop codon � 9) Release factors bind to stop codon instead of a t. RNA � 10) Ribosome, m. RNA, t. RNAs and protein all break apart

Mutations= changes in a cell’s DNA �Caused by: � 1) spontaneous errors � 2) mutagens: chemicals/radiation �Can happen in body cells (somatic cells) or �In reproductive cells (egg & sperm)

Somatic cell mutations �May cause no change = if mutated gene is one that is not use by that particular cell �May cause cell to die �May cause cancer �Not passed on to children

Thymine dimer

Reproductive Cell or Early Embryo Cell Mutations �Child with mutation �Every cell of the child is mutated �May cause miscarriage �May cause a genetic disorder in child �May have no effect at all

2 types of mutation �Gene mutation = DNA coding error � may be a missense mutation where the codons code for the wrong aa …. �or nonsense where stop codon or partial codon �Chromosome Mutation = change in chromosome number, missing or extra chromosome pieces.

Gene Mutations � 1) point mutations (substitutions) – change only 1 base pair � a) substitution of 1 nucleotide for another � b) ATT becomes ATG. . (missense) � c) may not cause any change = silent mutation � d) may change 1 amino acid � e) could be nonsense only if codes for stop � e) can cause disorder

� 2) Frameshift mutations- change all the codons � a) insertion � b) deletion � c) THE FAT CAT = HEF ATC AT � d) most always ruins protein

� 3) tandem repeats – codons repeated over & over � most often ruins protein � more repeats = more problems �

Transcripts �Transcript = chain of RNA as copied from DNA template Pre-m. RNA = a transcript that will become m. RNA Other transcripts become t. RNA or r. RNA

Transcript processing �Pre-m. RNA transcript has a cap added to 5’ end � cap facilitates exit through nuclear pore � cap aids in translation initiation � �cap is added to a short UTR on 5’ end of prem. RNA transcript (untranslated region) �UTR is followed by the START codon

Poly-A tail � 3’ end of transcript gets a poly-A tail added to it �Enzyme adds 50 -250 more A ribonucleotides �More As added make the m. RNA last longer �Fewer As make the m. RNA break down quicker �Breakdown starts immediately on entry to cytosol

RNA splicing �Introns = in between coding regions of RNA � do not code for a. a. s � are cut out before m. RNA leaves nucleus � bacteria do NOT have introns �Exons = have codons that are executed by translation…. code for a. a. s �Introns are cut out, exons fused together

Alternative splicing �Exons are spliced together in different orders �To make different proteins

spliceosome �Complex of proteins and small RNAs �Remove introns �Joins exons in proper order �RNAs in spliceosome are Ribozymes… � RNA enzymes �Sometimes the intron being removed IS the ribozyme

Evidence for RNA before DNA �RNA can act as its own enzyme �RNA polymerase can initiate polymerization on its own �DNA polymerase can only start polymerization at a primer �That is created by RNA polymerase

Post-translational modification �Amino acid modification – add functional groups �Trim aa from cap end �Cleave polypeptide into pieces �Join 2 polypeptide into quaternary structure � with disulfide bonds

Protein location w/i the cell �All translation begins in cytoplasm �For proteins destined for endomembrane system � (ER, golgi, lysosome, plasma membrane) �OR proteins produced for secretion (insulin) �The first few aa at leading end of polypeptide = signal peptide �Signal peptide binds to a Signal Recognition Particle (SRP) �SRP escorts ribosome to receptor protein on ER