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Title: AP 151 DNA Replication and Protein Synthesis Discovery of


1
AP 151 DNA Replication and Protein Synthesis
2
Discovery of the Double Helix
  • By 1900components of DNA were known
  • sugar, phosphate and bases
  • By 1953 x ray diffraction determined geometry of
    DNA molecule
  • Nobel Prize awarded in 1962 to 3 men Watson,
    Crick and Wilkins but not to Rosalind Franklin
    who died of cancer at 37 getting the x ray data
    that provided the answers.

3
DNA Structure Twisted Ladder
DNA molecule described as double helix.
4
Nucleotide Structure
  • DNA polymer of nucleotides
  • Each nucleotide consist of
  • phosphate group
  • sugar
  • ribose (RNA)
  • deoxyribose (DNA)
  • nitrogenous base
  • in this picture adenine

5
Nitrogenous Bases
  • Purines - double ring
  • guanine
  • adenine
  • Pyrimidines - single ring
  • uracil - RNA only
  • thymine - DNA only
  • cytosine both
  • DNA bases CTAG
  • RNA bases CUAG

6
Complementary Base Pairing
  • Nitrogenous bases united by hydrogen bonds
  • DNA base pairings
  • A-T and C-G
  • Law of complementary base pairing
  • one strand determines base sequence of other

Segment of DNA
7
DNA Function
  • Code for protein synthesis
  • Gene - sequence of DNA nucleotides that codes for
    one protein
  • Genome - all the genes of one person
  • humans have estimated 30-35,000 genes
  • other 98 of DNA noncoding junk or regulatory

8
DNA Replication 1
9
DNA Replication 2
  • Law of complimentary base pairing allows building
    of one DNA strand based on the bases in 2nd
    strand
  • Steps of replication process
  • DNA helicase opens short segment of helix
  • replication fork is point of separation of 2
    strands
  • DNA polymerase assembles new strand of DNA next
    to one of the old strands
  • 2 DNA polymerase enzymes at work simultaneously

10
DNA Replication 3
  • Semiconservative replication
  • each new DNA molecule contains one new helix and
    one conserved from parent DNA
  • Additional histones made in cytoplasm
  • Each DNA helix winds around histones to form
    nucleosomes
  • 46 chromosomes replicated in 6-8 hours by 1000s
    of polymerase molecules

11
Errors and Mutations
  • Error rates of DNA polymerase
  • in bacteria, 3 errors per 100,000 bases copied
  • Proofreading and error correction
  • a small polymerase proofreads each new DNA strand
    and makes corrections
  • results in only 1 error per 1,000,000,000 bases
    copied
  • Mutations - changes in DNA structure due to
    replication errors or environmental factors
  • some cause no effect, some kill cell, turn it
    cancerous or cause genetic defects in future
    generations

12
Cell Division
  • Essential for body growth and tissue repair
  • Mitosis nuclear division
  • Cytokinesis division of the cytoplasm
  • Occurs in most cells of the body
  • Not in RBCs, neurons, cardiac muscle
  • Produces 2 new cells with same number of
    chromosomes as parent cell

13
Mitosis
  • The phases of mitosis are
  • Prophase
  • Metaphase
  • Anaphase
  • Telophase

14
Cell Cycle
Cell Cycle
  • Interphase
  • Growth (G1), synthesis (S), growth (G2)
  • Mitotic phase
  • Mitosis and cytokinesis

Figure 3.30
15
Early and Late Prophase
  • Asters are seen as chromatin condenses into
    chromosomes
  • Nucleoli disappear
  • Centriole pairs separate and the mitotic spindle
    is formed

PLAY
Prophase
PLAY
Prometaphase
16
Chromatin
  • Threadlike strands of DNA and histones
  • Arranged in fundamental units called nucleosomes
  • Form condensed, barlike bodies of chromosomes
    when the nucleus starts to divide

Figure 3.29
17
Early Prophase
Pair of centrioles
Early mitotic spindle
Centromere
Aster
Chromosome, consisting of two sister chromatids
Early prophase
Figure 3.32.2
18
Late Prophase
Fragments of nuclear envelope
Polar microtubules
Kinetochore
Kinetochore microtubule
Spindle pole
Late prophase
Figure 3.32.2
19
Metaphase
  • Chromosomes cluster at the middle of the cell
    with their centromeres aligned at the exact
    center, or equator, of the cell
  • This arrangement of chromosomes along a plane
    midway between the poles is called the metaphase
    plate

PLAY
Metaphase
20
Metaphase
Metaphase plate
Spindle
Metaphase
Figure 3.32.4
21
Anaphase
  • Centromeres of the chromosomes split
  • Motor proteins pull chromosomes toward poles

PLAY
Anaphase
22
Anaphase
Daughter chromosomes
Anaphase
Figure 3.32.5
23
Telophase and Cytokinesis
  • New sets of chromosomes extend into chromatin
  • New nuclear membrane is formed from the rough ER
  • Nucleoli reappear
  • Generally cytokinesis completes cell division

PLAY
Telophase
24
Cytokinesis
  • Cleavage furrow formed in early telophase by
    contractile ring
  • Cytoplasm is pinched into two parts after mitosis
    ends

25
Telophase and Cytokinesis
Nucleolus forming
Contractile ring at cleavage furrow
Nuclear envelope forming
Telophase and cytokinesis
Figure 3.32.5
26
Protein Synthesis
  • DNA serves as master blueprint for protein
    synthesis
  • Genes are segments of DNA carrying instructions
    for a polypeptide chain
  • Triplets of nucleotide bases on DNA form the
    genetic library
  • Each triplet specifies coding for an amino acid
    a.a.s are the building blocks of proteins

27
Genetic Code
  • System that enables the 4 nucleotides (A,T,G,C)
    to code for the 20 amino acids
  • Base triplet
  • found on DNA molecule
  • nucleotides that stand/code for 1 amino acid
  • Codon
  • mirror-image sequence of nucleotides found in
    mRNA (ex AUG)
  • 64 possible codons (43)
  • often 2-3 codons represent the same amino acid
  • start codon AUG
  • 3 stop codons UAG, UGA, UAA
  • Remember, Uracil (U) replaces Thymine (T) in all
    RNAs

28
Roles of the Three Types of RNA
  • Messenger RNA (mRNA)
  • carries the genetic information from DNA in the
    nucleus to the ribosomes in the cytoplasm
  • Transfer RNAs (tRNAs)
  • bound to specific amino acids
  • base pair with the codons of mRNA at the ribosome
    to begin the process of protein synthesis
  • Triplet of bases on tRNA known as an anticodon
  • Ribosomal RNA (rRNA)
  • is a structural component of ribosomes

29
From DNA to Protein
Figure 3.34
30
Genetic Code
mRNA Codons
  • mRNA formed by transcription
  • DNA mRNA
  • mRNA codons code for amino acids according
  • to a genetic code on DNA
  • Different codons for the same a.a.
  • Universal same for all organisms

Figure 3.36
31
Transfer RNA (tRNA)
  • Activation by ATP binds specific amino acid (to
    green region) and provides necessary energy to
    join amino acid to growing protein molecule
  • Anticodon (see Loop 2 above) binds to
    complementary codon of mRNA aka, translation

32
Information Transfer from DNA to RNA
Figure 3.39
33
DNA and Peptide Formation
34
Alternative Splicing of mRNA
  • One gene can code for more than one protein
  • Exons can be spliced together into a variety of
    different mRNAs.

35
Protein Degradation
  • Nonfunctional organelle proteins are degraded by
    lysosomes
  • Ubiquitin attaches to soluble proteins and they
    are degraded in proteasomes

36
Developmental Aspects of Cells
  • All cells of the body contain the same DNA but
    develop into all the specialized cells of the
    body
  • Cells in various parts of the embryo are exposed
    to different chemical signals that channel them
    into specific developmental pathways
  • Genes of specific cells are turned on or off
    (i.e., by methylation of their DNA)
  • Cell specialization is determined by the kind of
    proteins that are made in that cell

37
Developmental Aspects of Cells
  • Development of specific and distinctive features
    in cells is called cell differentiation
  • Cell aging
  • Wear and tear theory attributes aging to little
    chemical insults and formation of free radicals
    that have cumulative effects throughout life
  • Genetic theory attributes aging to cessation of
    mitosis that is programmed into our genes
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