DNA, RNA, and Protein Synthesis

1
DNA, RNA, and Protein Synthesis

• Chapter 12
• Section 1-4

2
DNA 12-1

• 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.

3
Griffith Discovers

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

4
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.

5
Other Scientist

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

6
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)

7
Pictures of Watson and Crick, Rosalind Franklin
and her X-ray photos of DNA
8
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.

9
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.

10
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
  bases
• always lined up on the Sugars (deoxyribose)
• Nitrogen base (1 of 4)
• Adenine (A) purine
• Guanine (G) - purine
• Thymine (T) pyrimidine
• Cytosine (C) - pyrimidine
• See pg. 291, Fig. 12-5

11
Base Pairing Rule

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

12
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
  prize.
• See pg. 294, Fig. 12-7

13
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.
• See pg. 297, Fig. 12-10
• Chromosomes contain DNA proteins called
  histones.
• 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.

14
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
  DNA.
• Example template DNA TACGTT
• new DNA ATGCAA

15
DNA Replication
16
Process of DNA Replication See pg. 298, Fig.
12-11

• 2 strands separate.
• Replication forks form.
• New strands form.
• New bases are added (base pairing).
• Ex. TACGTT ATGCAA
• It is semi-conservative- 1 original strand and 1
  new strand.
• 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.

17
Can you write the corresponding Nitrogen Base?

• GAC TAT ATT GAC ATT GAG CCC TTA
• ATA GAG CAC GCA TAT CCG AGT TAT

18
Replication animation

• http//media.pearsoncmg.com/bc/bc_0media_ap/apflix
  /ap/ap_video_player.html?dna

19
Making Proteins

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

20
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.

21
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.

22
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

23
3 Types of RNAAll 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.
• See pg. 300, Fig. 12-12

24
Why make proteins?

• Needed for cell structure and movement, makes
  enzymes and nucleotides.

25
Transcription

• 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
• mRNA ACGUGCGU

26
(No Transcript)
27
Transcription animation

• http//www.pearsonsuccessnet.com/snpapp/iText/prod
  ucts/0-13-190404-3/bm/vadnatra.html

28
STILL CONFUSED?

• 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.

29
Genetic CodeSee pg. 303, Fig. 12-17

• 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
  acid.
• 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

30
TranslationSee pg. 304-5, Fig.12-18

• 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.

31
Translation

• 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
  read.
• 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.

32
Translation
33
Translation animation

• http//www.pearsonsuccessnet.com/snpapp/iText/prod
  ucts/0-13-190404-3/bm/vaprotei.html

34
What happens to mRNA at the ribosome?

• mRNA is transcribed from the DNA in the nucleus.
• mRNA moves into the cytoplasm attaches to a
  ribosome.
• 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.

35
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.

36
Mutations 12-4

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

37
Gene MutationsSee pg. 307, Fig. 12-20

• 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
  codons.
• 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.

38
Chromosomal MutationsSee pg. 308, Fig. 12-21

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