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DNA Replication and Protein Synthesis. Taylor Reich. January 8, 2010. Structure of DNA. Sugar+Phosphate+BasePair (A, G, C, or T)= Nucleotide (basic unit) Purrines- A, G; Pyrimedines- C, T A bonds with T- Double Hydrogen Bonded G bonds with C- Triple Hydrogen Bonded

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Dna replication and protein synthesis

DNA Replication and Protein Synthesis

Taylor Reich

January 8, 2010

Structure of dna
Structure of DNA

  • Sugar+Phosphate+BasePair(A, G, C, or T)=Nucleotide(basic unit)

  • Purrines- A, G; Pyrimedines- C, T

  • A bonds with T- Double Hydrogen Bonded

  • G bonds with C- Triple Hydrogen Bonded

  • Covalent Bonds- sugar- phosphate, sugar-basepair

  • 3’ and 5’ ends

  • DNA -> hystome -> nucleosome -> supercoil

    • Major/Minor Grooves- hollow center (Think Staircase)

  • Two Thins for DNA

    • DNA Replication (self-replicates)

    • Protein Synthesis





Dna replication in prokaryotes
DNA Replication in Prokaryotes

  • Enzymes read opposite directions

  • 500 Nucleotides/second

  • Origin of Replication

  • Ring DNA

Dna replication
DNA Replication

  • Semi-conservative

    • Half old DNA, half new DNA

  • DNA polymerase (replicates DNA)

    • Reads 3’->5’; Makes 5’->3’

Eukaryotic replication enzymes and their functions
Eukaryotic Replication: Enzymes and their Functions

  • DNA B- mark replication site

  • DNA gyrase- uncoil DNA

  • Topoisomerase- knick DNA (release tension)

  • rep(helicase)- split DNA (break hydrogen bonds)

  • SSB (single strand binding)- hold complimentary DNA apart

Eukaryotic replication enzymes and their functions1
Eukaryotic Replication: Enzymes and their Functions

  • RNA Primase- attach 10 RNA nucleotides

    • Okazaki fragments (lagging strand)

  • DNAPolymerase III- replicate okazaki fragments (lagging) DNA strand (leading)

  • DNA Polymerase I- replace RNA nucleotides with DNA ones (from primer)

  • Ligase- bond nicks from topoisomerase

Eukaryotic dna replication
Eukaryotic DNA Replication

  • 50 nucleotides/second

    • Leading and Lagging Strand

Protein synthesis
Protein Synthesis

  • Transcription

    • Make RNA from DNA

      • Nucleus

  • Translation

    • Make protein from RNA

      • Ribosome (cytoplasm)


[1] Splits DNA [2] Synthesizes RNA nucleotides [3] Re-bonds DNA

  • Parts of a gene:

  • RNA Polymerase makes RNA

    • Binds to promoter if it’s on, it moves to the start signal, synthesizes on RNA

Start signal

Stop Signal



ORF (random sequence)

Termination Sequence


on/off switch

  • Open Reading Frame

    • codes for protein


  • Have a mRNA strand from DNA

    • Add:

      • Cap: composed of 7 guanines; put on 5’ end

      • Tail: composed of 100-200 adenines; put on 3’ end

        • The more adenines attached, the longer the mRNA lasts

    • Remove:

      • SNRNP [Small Nuclear Ribo-Nuclear Protein]

        • Cuts out introns

        • Hooks together exons

      • [Spliceosome (SNRNPS&other proteins)]

  • Introns stay IN the nucleus; Exons EXIT the nucleus and continue on to the ribosome for translation…


Amino Acid

(each tRNA has specific amino acid)


(three nucleotides)


  • Ribosomes

    • Split/Come together all the time

    • Made up of two parts: small unit & large unit

  • tRNA (transfer RNA)

    • aminoacyl-tRNA synthetase

      • Whole group of slightly different enzymes. Each has 2 binding sites: 1) particular tRNA 2) particular amino acid


  • Step 1: small unit of ribosome binds with 5’ end of mRNA

  • Step 2: initiation factors(proteins) bind to mRNA and ribosome

  • Step 3: tRNA binds using initiating factors (on start signal of mRNA) (anitcodon binds)

    • Every start signal on mRNA is AUG (so tRNA nucleotide is UAC)

  • Step 4: Large unit of ribosome binds, leaving a space b/t the 2 parts of theribosome- the A-site, and the P-site

  • Step 5: knock off initiating factors, attach elongation factors- activate ribosome to do this:

    • Look for tRNA w/ completmentary anticodons to mRNA codon at the A-site

  • Step 6: peptidyl transferase forms a peptide bond b/t amino acids, and breaks bond between amino acid and tRNA at the P-site

  • Step 7: mRNA moves down 1 codon, tRNA at P-site, leaves, tRNA shifts, ribosome does it’s job, new tRNA arrives, whole process repeats

  • Result: A chain of Amino Acid, A.K.A. a PROTEIN

Transformation tidbits
Transformation Tidbits

  • The sequence of nucleotides on mRNA determines the correct order of the amino acid chain, determining the correct protein…or not

    • Frame Shifting- loosing/gaining a nucleotide- changes every codon= wrong protein produced

    • Substitution- affects only one codon- not always a different amino acid

      • “Wobble Affect”- if the first or second letter (base pair) are wrong, it will be a different amino acid, if the third letter is wrong, it may not be

  • Release/Termination factor- binds to P-site at the end of the mRNA chain, ribosomes split

  • Can be more than one ribosome on a mRNA chain at a time

  • Polycistronic: a messenger RNA that codes for more than one protein

Negative feedback

Stops the production

Negative Feedback

  • When DNA is read, producing enzymes, creating a product, the product concentration gets high. Two things can happen:

    • Product binds to the DNA

    • Product binds to the enzymes

  • When the concentration gets low enough, the product falls off of the DNA/enzymes, commencing production once again

  • Operator- b/t promoter and start signal

  • Regulator- before promoter, usually turned on being read, giving out mRNA. It makes the…

  • Repressor- a protein that binds to the operator, turning off the gene




Start Signal


Termination Signal

Negative feedback induction corepression cap
Negative Feedback:Induction, Corepression, & CAP

  • Inducer- a substrate that binds to repressor, deactivating it/knocking it off the DNA. The DNA is turned on. When it falls off the repressor, the repressor sits on the operator, turning off gene. It is called Induction

  • Sometimes, the product is the substrate for the inducer, so when there is a high concentration of product, it turnes off the gene. That is called Corepression

    • The product concentration is the important thing in these processes

  • Overriding the system is possible with CAP. Turns on the gene when cAMP sits on DNA, the DNA bends, knocking off the repressor, activating CAP, and the gene turns on

  • cAMP goes to mitochondria, gets phosphates, turns to ATP, CAP comes off DNA, DNA goes back to original shape, repressor binds w/ corepresser, sites on DNA, and the gene turns off

    • Can’t be done consciously

More on gene structure
More on Gene Structure

About 10,000

base pairs


  • DNA bends so that the Initiation Gene touches the Promoter, which is bond to the Transcriptional Factor Gene, the Enhancer Gene, and the DNA