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DNA, RNA, and Protein Synthesis


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Title: DNA, RNA, and Protein Synthesis

DNA, RNA, and Protein Synthesis
  • To understand genetics, biologists had to learn
    the chemical structure of genes.
  • Frederick Griffith- 1928 He tried to figure out
    how bacteria makes people sick like pneumonia.
    He injected mice with a mixture of heat-killed
    bacteria, disease-causing bacteria, live
    harmless bacteria. The result was that the mice
    developed pneumonia.

Griffith Discovers
  • Transformation disease causing bacteria pass
    the disease causing ability on to the harmless
    strain of bacteria.
  • One permanently changed another.

Other Scientists
  • Oswald Avery 1944 He his research group
    repeated Griffiths work and found that bacteria
    are transformed by DNA.
  • That DNA stores and transmits the genetic
    information from one generation of an organism to
    the next.

Other Scientist
  • Alfred Hershey Martha Chase 1952 They
    performed experiments with bacteriophages
    showed that genes are made of DNA.

Other Scientist
  • James Watson and Francis Crick created the first
    double helix model. ( they eventually won the
    nobel prize for it in 1962 for their work)
  • Rosalind Franklin also played a major role in
    the ladders discovery because Watson and Crick
    used her photos of the DNA ladder to assemble the
    model. (Unfortunately she died 4 years before
    nobel prize was awarded)

Pictures of Watson and Crick, Rosalind Franklin
and her X-ray photos of DNA
Hershey Chase
  • Bacteriophage bacteria eater a kind of virus
    that infects bacteria. See pg. 289, Fig. 12-3
  • Radioactive Markers used by Hershey Chase to
    determine which part of the virus (protein coat
    or the DNA coat) entered the infected cell. As a
    result, they could learn whether genes were made
    of protein or DNA.
  • 32P 35S Phosphorous 32 is not often found in
    protein and Sulfur 35 in not found in DNA.
  • The presence of 35S in bacteria means that the
    viruses protein was in the bacteria.
  • The presence of 32P in bacteria means the DNA was
    in the bacteria.
  • Conclusion Genetic material of bacteriophage
    was DNA, not protein.

What is DNA?
  • Deoxyribonucleic acid is the nucleic acid
  • stores the genetic code.
  • Contains the blueprints for making proteins.
  • Genetic codes program of the cells how cells
    store information they pass from one generation
    to the next.
  • DNA is a polymer (large molecule)formed from
    units called nucleotides.

Location Structure of DNA
  • Location
  • in the nucleus of eukaryotic cells.
  • In the cytoplasm of prokaryotic cells.
  • Structure
  • Double stranded (double helix)
  • Composed of 3 part nucleotides
  • Deoxyribose (5 carbon sugar)
  • Phosphate group (PO4)
  • Note The two alternate S-P-S-P with the nitrogen
  • always lined up on the Sugars (deoxyribose)
  • Nitrogen base (1 of 4)
  • Adenine (A) purine
  • Guanine (G) - purine
  • Thymine (T) pyrimidine
  • Cytosine (C) - pyrimidine

Base Pairing Rule
  • Hydrogen Bonds
  • hold the nitrogen
  • bases together in
  • the middle
  • Adenine pairs with Thymine
  • Cytosine pairs with Guanine

Structure cont.
  • Purines have 2 rings in their structure.
  • Pyrimidines have 1 ring in their structure.
  • Double Helix 2 strands wound around each other
    twisted ladder.
  • Base pairing hydrogen bonds hold 2 strands
    together can form between certain base pairs.
    A-T, T-A, G-C, C-G
  • Discovered by Watson Crick and won a nobel

Chromosomes DNA Replication (synthesis) 12-2
  • DNA is very long must fold up tightly to fit
    inside a cell. Ex. Trying to pack a 300m length
    rope into a backpack.
  • Chromosome Structure
  • DNA is wound around proteins.
  • DNA proteins wind together to form nucleosomes.
  • Nucleosomes pack together to form thick fiber.
  • Chromosomes contain DNA proteins called
  • Most of the time nucleosomes are spread out the
    chromosomes are not visible but during mitosis,
    the nucleosomes become more tightly packed the
    chromosomes can be seen under a microscope.

DNA Replication
  • Each strand of DNA serves as a template for a new
    strand of DNA
  • During cell reproduction an exact copy of the
    parent cell DNA is made.
  • Enzymes unzip DNA (separates) breaking hydrogen
    bonds between bases.
  • 2 strands unwind.
  • 2 new strands form using Base pairing.
  • DNA replicates itself exactly so that each new
    cell will have an identical copy of the original
  • Example template DNA TACGTT
  • new DNA ATGCAA

DNA Replication
Process of DNA Replication
  • 2 strands separate.
  • Replication forks form.
  • New strands form.
  • New bases are added (base pairing).
  • It is semi-conservative-
  • 2 DNA molecules identical to each other to the
    original molecule.
  • DNA polymerase enzyme that unzips DNA molecules
    when hydrogen bonds b/w the base pairs are
    broken. 2 strands unwind join nucleotides.

Can you write the corresponding Nitrogen Base?

Replication animation
  • http//media.pearsoncmg.com/bc/bc_0media_ap/apflix

Making Proteins
  • DNA contains the instructions for building
  • Proteins are made at the ribosomes
  • DNA cannot leave the nucleus
  • How does DNAs information get to the ribosome?

RNA Protein Synthesis 12-3
  • Genes coded DNA which contain instructions for
    assembling proteins.
  • The first step in decoding the genetic messages
    is to copy part of the nucleotide sequence from
    DNA into RNA.

What is RNA?
  • Ribonucleic acid
  • mRNA nucleic acid that acts as a messenger b/w
    DNA ribosomes carries the genetic code for
    making proteins from the amino acids.
  • RNA is a disposable copy of a segment of DNA.
  • RNA has 1 job (protein synthesis) controlling
    the assembly of amino acids into proteins.
  • Contains coded information for making proteins.

Location Structure of RNA
  • Location
  • In the nucleus
  • Cytoplasm
  • Ribosome
  • Structure
  • Single Strand
  • Nucleotides composed of
  • Ribose (5-carbon sugar)
  • Phosphate group
  • Nitrogen bases
  • Adenine (A)
  • Guanine (G)
  • Cytosine (C)
  • Uracil (U)
  • RNA does not contain thymine but has uracil

3 Types of RNA All are involved in Protein
Synthesis are copied from the DNA
  • Messenger RNA (mRNA) carry copies from DNA to
    rest of cell.
  • Ribosomal RNA (rRNA) it is on the ribosomes
    where proteins are assembled.
  • Transfer RNA (tRNA) transfers each amino acid
    to the ribosome according to the coded messages
    in mRNA.

Why make proteins?
  • Needed for cell structure and movement, makes
    enzymes and nucleotides.

  • The process in which a molecule of DNA is copied
    into a complementary strand of RNA.
  • Occurs inside the nucleus b/c DNA is in the
    nucleus cant leave so a messenger RNA (mRNA)
    must bring the genetic information from the
    nucleus to the ribosomes in the cytoplasm.
  • Steps
  • RNA polymerase enzyme that attaches to DNA
    moves along it unwinding the two strands
  • Promoters signals in the DNA that indicate to
    the RNA polymerase where to bind.
  • The instructions for making proteins are
    specified by genes are found in the 4
    nitrogenous bases.
  • Example DNA TGCACGCA

(No Transcript)
Transcription animation
  • http//www.pearsonsuccessnet.com/snpapp/iText/prod

  • Imagine that you are a mechanic. The repair
    manual that you use is the DNA ladder.
  • If you wanted to copy the instructions to install
    a radio in your car, would you copy the entire
    repair manual?
  • NO!!! You would only copy the portion pertaining
    to installing the radio. That is what
    transcription does.

Genetic Code
  • The genetic code is read 3 letters at a time, 3
    bases long.
  • Proteins are determined by the order in which
    amino acids are joined together
  • Codon 3 letter word composed of 3 nucleotides
    on mRNA
  • Each codon codes for a particular amino acid
    while chains of amino acids form proteins.
  • With 4 bases, there are 64 possible 3-base codons
    there can be more than 1 codon for each amino
  • There are start and a stop codons.
  • Ex. This RNA sequence UCGCACGGU
  • Read 3 bases at a time UCG-CAC-GGU
  • Different amino acids UCG Serin -
    CAC Histidine GGU Glycine

  • The process of building a protein molecule
    according to code in mRNA.
  • During the process transfer RNA (tRNA) carries
    amino acids to the ribosomes where the amino
    acids are joined to form the protein
  • Ribosomes are where proteins are made.

  • Steps of translation
  • tRNA binds to the mRNA
  • A start codon starts the protein chain
  • tRNA contain 3 complementary nucleotides to the
    mRNA called the anticodon once it matches it
    leaves behind an amino acid and the next codon is
  • more tRNA molecules will come together to create
    the next polypeptide
  • Once a stop codon is read, the new polypeptide
    chain is released as a new protein.

Translation animation
  • http//www.pearsonsuccessnet.com/snpapp/iText/prod

What happens to mRNA at the ribosome?
  • mRNA is transcribed from the DNA in the nucleus.
  • mRNA moves into the cytoplasm attaches to a
  • tRNA will read mRNA in 3 part sections (codons).
  • tRNA carries amino acids to the ribosome.
  • A polypeptide assembly line forms.
  • Amino acids bond to form proteins.

Role of RNA DNA
  • Compare RNA DNA to Builders
  • A master plan has all the information needed to
    construct a building. But builders never bring
    the valuable master plan to the site where it
    could get damaged or lost. They prepare
    inexpensive, disposable copies of the plan called
    blueprints. The master plan is safe inside the
    office while the blueprints are taken to the job
    site. Similarly, the cell uses the vital DNA
    master plan to prepare the RNA blueprints.
    The DNA is safe in the nucleus, while the RNA
    goes to the protein-building sites in the
    cytoplasm the ribosomes.

  • Mutations are changes in the genetic material.
  • 2 Kinds
  • Gene mutations
  • Chromosomal mutations

Gene Mutations
  • Produce changes in a single cell.
  • Types
  • Point mutations involves changes in one or a
    few nucleotides and occur at a single point in
    the DNA sequence.
  • Substitutions one base is changed to another
    only affects a single amino acid.
  • Insertions Deletions a base is inserted or
    removed from the DNA sequence much more dramatic
    because the genetic code is read in 3-base
  • Frameshift mutations the shifting of codons
    the reading frame which may change every amino
    acid that follows the point of the mutation. It
    can alter a protein so much that it is unable to
    perform its normal functions.

Chromosomal Mutations
  • Produce changes in whole chromosomes.
  • Types
  • Deletions involve the loss of all or part of a
  • Duplications produces extra copies of parts of
    a chromosome.
  • Inversions reverse the direction of parts of a
  • Translocation when part of one chromosome
    breaks off attaches to another.
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