Nucleic Acids and Protein Synthesis

Nucleic Acids DNA Deoxyribonucleic Acid RNA Ribonucleic Acid

DNA Double stranded helix Never leaves the nucleus Watson, Crick, Wilkins won Nobel Prize in 1962 Franklin died in 1958 never recognized

DNA

Nucleotide Building Blocks of nucleic acids are NUCLEOTIDES! Phospate group Sugar molecule (deoxyribose) Nitrogenous bases

Nitrogenous Bases of DNA

How do the N-Bases pair up? A-T (2 bonds) G-C (3 bonds)

How Does DNA Replicate? 1. double helix unwinds 2. Each chain serves as a template for new nucleoide chain 3. point at which 2 chains separate is called the REPLICATION FORK. 4. HELICASE = the enzyme that separates the chains (breaks H bonds) 5. DNA POLYMERASE moves along the chains and helps assemble new nucleotides forming new chains (3’ to 5’ ONLY) DNA LIGASE – ligates 5’ to 3’ (DNA polymerase brings the nucleotides)

DNA replication continue… The 3’ sugar has an –OH GROUP The 5’ sugar has a PHOSPHATE GROUP LEADING STRAND – formed from 3’-5’ LAGGING STRAND – formed from 5’- 3’ with the help of DNA LIGASE! OKAZAKI FRAGMENTS – fragments that will be ligated together

Can you see how DNA is making an exact copy of itself! *

This a little more difficult Can you figure out the diagram?

Simplest Illustration of DNA replication…

What is a mutation?? A CHANGE in the nucleotide sequence at even ONE location!!

Protection About 1 in a billion nucleotides in DNA is INCORRECTLY paired. DNA polymerase proofreads and removes nucleotides that base pair incorrectly. DNA polymerase & DNA ligase  also repair damage caused by ultraviolet light, xrays, and toxic chemicals

Archibald Garrod 1909 English Physician Suggested that genes dictate phenotypes through enzymes, the proteins that catalyze chemical processes in the cell GENOTYPE  genetic make up PHENOTYPE  physical appearance DNA –(transcription) RNA –(translation) protein synthesis Genotype ------ phenotype

Garrod 1900’s Children -> defect in 2 a.a. due to defect in the enz. That helps make the a.a Phenylalanine->PKU Tyrosine ->albinism Geneenzymeamino acid (can’t be made) Couldn’t prove it due to lack of technology

George Beadle & Edward Tatum 1940’s American Geneticists ONE GENE ONE ENZYME (polypeptide) HYPOTHESIS: the function of a gene is to dictate the production of a specific enzyme. Experimented with bread mold  lacked an enzyme in a metabolic pathway that produced some molecules that mold needed to produce an amino acid called arginine.

Tatum & Beadle 1958 Nobel Prize Proved Garrod correct Bread mold -> can make all of it’s own a.a. that it needs Gene -> enzyme -> amino acid One gene = enzyme One gene = one protein!!

RNA RIBONUCLEIC ACID SINGLE STRANDED RESPONSIBLE FOR BRINGING THE GENETIC INFO. FROM THE NUCLEUS TO THE CYTOSOL!

RNA Nucleotide Phosphate group Sugar molecule (ribose) Nitrogenous bases Adenine – URACIL Cytosine - guanine

3 Kinds of RNA mRNA – (messenger) brings info from DNA in nucleus to cytosol in eukaryotic cells (uncoiled) tRNA –(transfer) brings amino acids to mRNA for translation (hairpin shape) rRNA –(ribosomal) most abundant, rRNA makes up the ribosomes where proteins are made (globular)

TRANSCRIPTION!! DNA  RNA 1.RNA polymerase-initiates transcription by binding to region on DNA called PROMOTER (causes DNA to separate)-INITIATION PHASE 2. only ONE of the DNA chains will be used for transcription it’s called the TEMPLATE (promoter dictates which of the two strands will be used) 3. RNA POLYMERASE – attached to first DNA nucleotide of template chain – then begins adding complementary RNA nucleotides- ELONGATION PHASE

Cont. Transcription 4. transcription continues until RNA polymerase reaches a TERMINATION SIGNAL on the DNA-TERMINATION PHASE 5. RNA polymerase releases both the DNA mol. And newly formed RNA mol. Are transcribed in this way (all three!!!)

RNA *

RNA replications *

PROKARYOTES Transcription and translation occur in the SAME place! NO NUCLEUS!

Eukaryotes 1. Before RNA leaves the nucleus: G (guanine) cap is attached A (adenine) tail is attached “many” 2. These protect the RNA from attack by cellular enzymes and help ribosomes to recognize the mRNA (cap & tail are NOT translated)

Cont. Eukaryotes 3. INTRONS (non coding sequence) are removed 4. EXONS (part of gene that are expressed) are joined to produce a mRNA molecule with a continuous coding sequence. NOW RNA CAN LEAVE THE NUCLEUS!

Protein Synthesis PROTEINS CARRY OUT THE GENETIC INSTRUCTIONS ENCODED IN AN ORGANISM’S DNA!!!!

TRANSLATION The process of assembling from info. Encoded in a mRNA! 1. mRNA leaves nucleus 2. mRNA migrates to ribosome in cytosol for protein synthesis 3.amino acids floating in cytosol are transported to ribosomes by tRNA molecule 4. peptide bonds join the amino acids to make polypeptide chain

Vocabulary! 1. GENETIC CODE: correlation between a nucleotide sequence and an amino acid sequence 2. CODON 3 mRNA nucleotides, codes for a specific amino acid (64) 3. START CODON (AUG) & a.a. methionine 4. STOP CODON (UAA, UAG, UGA) 5. ANTICODON – 3 tRNA nucleotides carrying a specific amino acid!

Protein Synthesis *

Protein Synthesis *

Protein Synthesis !

THE SUMMARY! *

Ribosome factory for polypeptides Two subunits: Large subunit (top) Small subunit (bottom)

P site – holds tRNA carrying growing polypeptide A Site – holds tRNA carrying the next amino acid to be added *

Initiation Codon Marks the Start of an mRNA message 3 PHASES: 1. INITIATION 2. ELONGATION 3. TERMINATION

INITIATION ( 2 steps) A) An mRNA mol. Binds to a small ribosomal subunit. A special initiator tRNA binds to the specific codon called the START CODON (UAC binds to start codon AUG  methionine) B) A large ribosomal subunit binds to the small one creating a functional ribosome. The initiator tRNA fits into the P site of the ribosome.

Elongation and Termination Elongation adds amino acids to the polypeptide chain until a stop codon terminates translation.

3 Steps of Elongation 1. Codon recognition  anticodon of incoming tRNA carrying amino acid pairs with mRNA codon in A site. 2. Peptide bond formation  polypeptide separates from tRNA (fr. P site). Peptide bond forms between amino acid in P & A site  ribosome catalyzes formation of bond. CONTINUE…..

CONTINUE… 3. Translation  P site tRNA now leaves ribosome, the ribosome translocates (moves) the tRNA in the A site, with its attached polypeptide to the P site. The codon and anticodon remain bonded and the mRNA and tRNA move as a unit . This movement brings into the A site the next mRNA codon to be translated and process can start again! ELONGATION CONTINUES UNTIL A STOP CODON REACHES A SITE.