Nucleic acids and protein synthesis

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Nucleic acids and protein synthesis

• Chapter 10

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DNA

• Structure discovered by Watson Crick in 1953
• Pentose sugar called Deoxyribose

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X ray diffraction data to support DNA structure

• Rosalind Franklin
• In 1953, X-ray diffraction experiments
• In 1962, after Franklin's death, Watson, Crick,
  and.

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DNA molecules

• Deoxyribonucleic acid
• Double helix
• Found in the nucleus only
• Organic compound
• S.P. CHON

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Fig. 03-01
Fig. 03-01DNA structure and location
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DNA

• Double stranded
• Adenine--A
• Thymine--T
• Guanine---G
• Cytosine---C
• Found in the nucleus only

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Nucleotides

• Nitrogen containing bases
• A adenine
• T thymine
• G guanine
• C cytosine
• 3 billion pairs in human genome

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Do we copy everything all of the time?

• 3 billion nitrogen pairs
• 25,000 genes
• All working??
• WHICH ONES DO WE WANT TO WORK???

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DNA

• Determines the structure and the activity of the
  cell
• (A) Cells framework
• (B) Enzymes for chemical reactions
• (C) Chemical messengers (hormones)

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Bonds in ladder

• Phosphodiestersides of ladderstrong
• Hydrogen bonds---nitrogen basesweaker
• Why is there a difference in the strength of the
  bonds?

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Unwinding of DNA by helicases expose the DNA
bases (replication fork) so that replication can
take place.
DNA replication
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DNA Strand

• To make a copyreplication of DNA
• Untwist the ladder
• Separate the pairs---not all at one time
• HELICASESenzymes that creates replication
  forkseparation
• IMPORTANT TO ALL LIVING THINGS
• DNA polymerases create pairs to copyleading
  strand (Sense strand)

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What pairs up?

• DNA strand
• A-T-T G-C-C C-A-T C-A-A
• What is the DNA complementary strand?

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Complementary DNA

• C-C-C A-C-A T-T-A G-G-T C-T-A
• A-G-T G-G-G A-A-C C-C-T G-A-A
• C-C-G C-A-A T-T-C G-T-T T-A-G

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Proofreaders

• Enzymes that correct errors
• Not perfect
• Some agents alter the code
• UV rays, chemicals, radiation from X-rays,
  smoking, drinking, cell phones give off radiation
  (switch ears more often), portable phones (switch
  ears)

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UV rays-mutation
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Mutations

• Good, bad, no problem?

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RNA-Ribonucleic acids

• Single stranded
• Copies DNA
• Four kinds
• Messenger RNA
• (transcription)
• In nucleus
• Uracil replaces thymine
• A-U
• G-C

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Transcription

• Rewriting/copying of the genetic information from
  DNA
• Messenger RNA (m-RNA)
• DNA is the templatecopy and leave the nucleus
  through nuclear pores

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Translating the code

• DNA Interactive

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Translation

• Transcribe and Translate a Gene
• http//gslc.genetics.utah.edu/units/basics/transcr
  ibe/

Translate
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DNA Transcription

• DNA must be copied to messenger RNA (mRNA)
• mRNA goes from nucleus to the ribosomes in
  cytoplasm
• mRNA complements known as codons
• Only 3 nucleotide letters long
• Remember RNA has uracil (U) instead of thymine
  (T)!

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Transcription Step I
Template DNA Strands
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Transcription Step II
Template DNA is Matched Up with Complementary
mRNA Sequences
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Transcription Step III
mRNA leaves nucleus and goes to ribosomes
A new complementary RNA strand is made (rRNA)
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Codonm-RNA

• DNA
• A-C-C G-T-A C-G-G A-TA
• Messenger RNA????

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This is a molecule of messenger RNA. It was
made in the nucleus by transcription from a DNA
molecule.
codon
mRNA molecule
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A ribosome on the rough endoplasmic reticulum
attaches to the mRNA molecule.
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tRNA structure

• 3-base code (triplet) is an anticodon
• Protein molecule
• Attached amino acid that is carried from
  cytoplasm to ribosomes

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Transcription only one of the DNA strands is
copie
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A transfer RNA molecule arrives.
It brings an amino acid to the first three bases
(codon) on the mRNA.
The three unpaired bases (anticodon) on the tRNA
link up with the codon.
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Another tRNA molecule comes into place, bringing
a second amino acid.
Its anticodon links up with the second codon on
the mRNA.
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A peptide bond forms between the two amino acids.
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A peptide bond joins the second and third amino
acids to form a polypeptide chain.
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The process continues.
The polypeptide chain gets longer.
This continues until a termination (stop) codon
is reached.
The polypeptide is then complete.
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Structure and Function of Proteins

• Made up of subunits called amino acids (20
  different AAs)
• Specific sequence of amino acids dictates
  specific protein

• Proteins can be structural (muscles) or enzymes
  catalyze (speed up) chemical reactions or hormones

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Translation

• Occurs in cytoplasm
• Synthesis of polypeptide (many amino acids
  bonded together) under direction of mRNA
• mRNA tells rRNA which amino acid to go get from
  cytoplasm
• rRNA and protein in ribosome binds amino acids
  together in sequence directed by mRNA

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Practice Table
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Proteins to be made

• Polypeptides---many peptide bonds
• Many amino acids
• Chart
• PROTEINS50 or more amino acids
• Insulin51 amino acids in code

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Overview of Transcription and Translation
Transcription
Translation
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Hormones

• Insulin---51 amino acidscontrols blood sugar
• Leptin167 amino acidssuppresses hunger pains
• HGHHuman growth hormone191 a.a.promotes uptake
  of proteins by body
• Prolactin198 a.a.promotes lactating

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Translation

• Messenger RNA
• A-C-C G-G-C U-A-U C-C-G A-G-G
• Transfer RNA??

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What we just talked about in video form

• DNA Interactive

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Dark means it is inactive
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Start copying !!!

• Amino Acid Chart
• Check it out!!
• Promotes the code!!
• Keep going until????

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DNA and protein synthesis

• DNA IS UNWOUND
• mRNA is made
• mRNA matures
• mRNA attaches at ribosome
• tRNA matches codon
• Peptide bonds are formed
• Stop codon is read
• mRNA and protein are released

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Exons and introns

• Exons are what we want to copying
• Introns are the junk DNA
• DNA is copied
• Nuclear RNA---copies the junk and all
• mRNAjust the exons
• 20,000 to 35,000 genes
• 3 billion nucleotides (base-pairs)

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Nuclear RNA

• XXXXXBBBBBNNNNDORRRRRRYOULIKEHHHHHHHHHTODISSECTANI
  MALSBBBBBBBBBB
• Transcribe it as the messenger RNA would do
  (transcription)
• What is the message to be carried out to the
  ribosomes? (translation)

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Genes

• It is all more complex than we ever thought as we
  continue to study the genes
• Some introns are really long!!
• Polypeptide phraseAll of the letters to code for
  the amino acids
• YYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYCCCCCCCCCCCCC
  CCCCCCCKKKKKKKKKKKKKKKHELLOTTTTTTTTTTTTTTTTTTTTTTT
  TTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTT

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Long introns

• Why did they develop?
• Maybe it was a way to prevent DNA or RNA to be
  used by bacteria or viruses as a vector for
  diseases (way to transmit)
• StudiesLooking into introns may be copied and
  could be related to cancerlung, bladder,
  melanomas

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Mutations in noncoding

• May affect exons
• JJJJJUSTSTAYOUTBBBBBBBBOFTHESTORMANDYOUNNNNNNNNNNN
  NNNNWILLBESAFEFROMFROMFROMFROMFROMKKKKKKKKKKKKKKKK
  KKKKKKKKKHARMXXXXXXXXXXXXX

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Gene information on Chromosome 1

• 2,514 genes
• 22,345 exons
• 19,831 introns
• Shortest gene has 78 base pairs
• Exons-2 base pairs and 1 base pair in intron
• Longest gene has 980,961 base pairs
• 8,449 base pairs in exons and 476,158 base pairs
  in introns (in a row)

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Paper Instructions

• Helicasecame in and separated the DNA
• mRNA transcripted it
• Here is your strand of polypeptides made of the
  Nuclear RNA
• What does it say???

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INSTRUCTIONS

• RNA splicers ---take out the introns
• DirectionsNote the XX codes. Fold at the first
  one you come upon and then the next XX code to
  eliminate the introns
• Continue to do so throughout the strand
• WHAT IS THE MESSAGE?

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DNA

• DNA Interactive

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Quizzes

• Structure and chemical composition of DNA

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Promoter

• http//www-class.unl.edu/biochem/gp2/m_biology/ani
  mation/gene/gene_a2.html
• Promoter