Honors Biology Chapter 8

1
Honors Biology Chapter 8

• From DNA to Proteins

2
Section 8.1 Identifying DNA as the Genetic
Material

• Three major experiments led to the conclusion
  that DNA is the genetic material in cells.
• These experiments were performed by Griffith,
  Avery, Hershey, and Chase.

3
Summarize Frederick Griffiths experiment

• Griffith experimented with two types of bacteria
  S strain with sugar capsule (causes pneumonia and
  victim dies) and R strain without capsule (does
  not cause pneumonia and victim lives)
• Mice injected with regular S strain died
• Mice injected with heat-killed S strain lived
• Mice injected with R strain lived
• Mice injected with combination of R strain and
  heat-killed S strain died R strain had
  transformed into S strain

4
(No Transcript)
5
What was the conclusion of his experiment?

• Conclusion Some material must have been
  transferred from the heat-killed S strain to the
  live R bacteria he called the mystery material
  transforming principle which caused the
  harmless R bacteria to become disease-causing S
  bacteria

6
Summarize Oswald Averys experiment and what was
the conclusion of his experiment?

• Avery used enzymes to break down proteins, RNA,
  and DNA in transformed R bacteria. He found the
  following
• R strain bacteria that lacked protein could
  transform into S strain bacteria
• R strain bacteria that lacked RNA could transform
  into S strain bacteria
• R strain bacteria that lacked DNA could not
  transform into S strain bacteria
• Conclusion DNA is the transforming principle

7
What was the significance of Alfred Hershey and
Martha Chases experiments?

• Alfred Hershey and Martha Chase confirmed Averys
  findings with the use of bacteriophages (viruses
  that infect bacteria)
• They found that DNA from the bacteriophage
  entered the bacterium and protein did not.
• This convinced scientists that DNA is genetic
  material.

8
Section 8.2 Structure of DNA

• DNA (deoxyribonucleic acid) contains the
  information of life
• It holds the blueprints (instructions) for
  making essential proteins that are needed for
  life
• Proteins form the structural units of cells

9
What type of polymer is DNA? What is the monomer
of DNA?

• DNA is a very long molecule that is capable of
  holding lots of information
• It is a nucleic acid (as is RNA) and is composed
  of nucleotides.

10
Draw a nucleotide and label the parts of a
nucleotide.

• Each nucleotide consists of these 3 parts
• Sugar (deoxyribose)
• Phosphate
• Nitrogen base (guanine, thymine, cytosine, or
  adenine)
• A nucleic acid is a series of nucleotides.

11
(No Transcript)
12
What are the four nitrogen bases found in DNA?
How many rings do each contain in their
structural formula?

• There are two main categories of bases purines
  and pyrimidines.
• The purines consist of two rings. Guanine and
  adenine are purines.
• The pyrimidines consist of one ring. Cytosine and
  thymine are pyrimidines (notice all three of
  these words have a y in themuse that to help
  you remember).
• See page 231Figure 8.4

13
What are Chargaffs rules?

• Erwin Chargaff found that the amount of adenine
  is always equal to the amount of thymine and the
  amount of cytosine is always equal to the amount
  of guanine

14
Who are the two men credited with the discovery
of DNA structure as a double helix?

• James Watson and Francis Crickusing research
  collected by Erwin Chargaff, Linus Pauling,
  Maurice Wilkins and Rosalind Franklinproposed
  the double helix structure of DNA in 1953.

15
Whose work did they use to come to their
discovery?

• Erwin Chargaff
• Linus Paulingfound that the structure of some
  proteins was a helix or spiral this helped in
  Watson and Cricks hypothesis in the structure of
  DNA
• Rosalind Franklin and Maurice Wilkinsused X-ray
  crystallography that showed the DNA molecule
  resembled a coiled helix and was composed of two
  chains of nucleotides

16
Rosalind Franklin
17
Define double helix.

• Two strands of DNA wind around each other like a
  twisted ladder
• DNA consists of many nucleotides in the form of a
  double helix (spiral).
• The sugars and phosphates comprise the
  backbone, and the bases pair on the inside.

18
What are the base-pairing rules?

• Adenine Thymine (just remember the word at)
• Cytosine Guanine
• The base pairs are held together by weak hydrogen
  bonds.
• Adenine forms two hydrogen bonds with thymine,
  while cytosine forms three hydrogen bonds with
  guanine

19
Draw a section of DNA and label the bonds,
nitrogen bases, sugars, and phosphates in your
drawing.
20
DNA Structure Characteristics Recap

• Nucleotides bond to each other to form one strand
• Two strands bond to each other (via complementary
  base pairing) to form the double stranded DNA
  molecule
• Two strands twist to form the double helix
  (visualize a ladder that is twisted)
• Sides of the ladder are formed by alternating
  sugar and phosphate units which are covalently
  bonded
• Rungs of the ladder consist of bonded pairs of
  nitrogen bases (they are joined by weak hydrogen
  bonds)
• Rungs of the ladder are always uniform in length
  because one base is always a purine (2 ring) and
  the other is always a pyrimidine (1 ring) A-T,
  C-G

21
Extra Notes on DNA Structure

• Complementary strands the arrangement of
  nitrogen bases along one strand is the exact
  complement of the bases on the other strand.
• Ex if one strand is ATTCGCCA, then the other
  strand is TAAGCGGT.
• Note that the sequence of DNA is not randomit
  serves as a code for the making of proteins.

22

• Even though DNA is composed of only four
  different nucleotides, millions of different
  combinations and sequences can be made.
• Two Primary Activities of DNA
• Segments of DNA called genes store information
  for making proteins
• It can copy itself exactly for new cells

23
Section 8.3 DNA Replication

• Occurs in the nucleus
• When the two complementary strands of DNA are
  separated, each strand can serve as a pattern to
  make a new complementary strand.
• Enzymes and other proteins do the actual work of
  replication not DNA.

24
Replication Process (pages 236-237)

• An enzyme, DNA helicase, unwinds the two
  complementary strands of DNA and breaks the
  hydrogen bonds between nitrogen bases that hold
  the strands together Unzipping the DNA
• Nucleotide bases floating free in the nucleus
  bond with unpaired bases that are now exposed on
  each strand
• The complementary bases bond via hydrogen bonds
  by DNA polymerase
• Two new DNA molecules are formed that are exact
  replicas of the original DNA

25
(No Transcript)
26

• When DNA is unzipped, replication proceeds on
  both strands in opposite directions.

27
Replication Mistakes

• DNA is copied many sections at a time, so it goes
  quickly. DNA is copied very accurately because of
  proofreading mechanism in DNA polymerase.
• If a mistake is made, this enzyme can backtrack
  and replace the wrong nitrogen base.

28
Prokaryotic and Eukaryotic Replication

• Because prokaryotic DNA is a single loop,
  replication begins at one place along the loop
• Replication occurs in opposite directions until
  both replication forks meet
• Eukaryotic DNA is linear and replication occurs
  at many sites along a chromosome
• This allows faster replication than prokaryotic
  replication
• Replication bubbles are formed along the
  chromosome (Figure 8.9 on page 238)
• Replication of an entire human chromosome occurs
  in about eight hours

29
Section 8.4 Transcription

• Francis Crick defined the Central dogma of
  molecular biology stating that information goes
  from DNA to RNA to proteins
• The central dogma involves three processes
• Replicationmaking copies of DNA from DNA
• Transcriptionmaking copies of DNA in the form of
  RNA
• Translationtaking RNA to make a chain of amino
  acids or protein

30
RNA

• DNA stores and transmits the information needed
  to make proteins but it does not actually use
  that information to make proteins.
• That is the function of RNA, ribonucleic acid.

31
RNA vs. DNA
RNA DNA
Long chain molecule made of nucleotide subunits Long chain molecule made of nucleotide subunits
Single strand of nucleotides Double strand of nucleotides
Ribose as 5 carbon sugar Deoxyribose as 5 carbon sugar
Composed of G, C, A, U (uracil) Composed of G, C, A, T (thymine)
32
Three types of RNA

• mRNA (messenger)
• carries genetic information from DNA to the
  cytoplasm (site of translation)
• serves as a pattern for assembly of amino acids
• tRNA (transfer)
• brings amino acids from the cytoplasm to a
  ribosome to make growing protein
• each tRNA bonds to a specific amino acid
• rRNA (ribosomal)
• part of ribosomes
• site of protein synthesis

33
Transcription

• Transcription is similar to DNA replication in
  that a strand of DNA is used a template to make
  copies.
• One strand of DNA is the sense strandthis is
  the strand used for coding the mRNA sequence.
• The other is the antisense (on nonsense) strand
  and is not used for the mRNA.

34
Summary of Transcription

• 1. RNA polymerase binds to DNA and unzips it
• 2. RNA polymerase will add and link RNA
  nucleotides to the DNA template as it reads the
  gene
• Hydrogen bonds form between bases of unzipped
  DNA and RNA nucleotides
• 3. When the stop signal is reached, RNA is
  released from DNA strand

35
Triplet Code

• A codon is a three-nucleotide sequence on mRNA
  that codes for an amino acid
• Each codon codes for an amino acid, stop codon,
  or start codon (methionine)
• See page 244 in your textbook for the Genetic
  Code of mRNA codons.

36
Codon Chart on page 244

• You must know how to use this chart also!

37
Codon Wheel

• Remember, the codon on the mRNA corresponds to
  the amino acid!

38
Translation

• After transcription, RNA moves from the nucleus
  to the cytoplasm to make proteins. The
  translation occurs on ribosomes.
• start codon signals ribosome to start reading
  the mRNA strand
• (start AUG )
• stop codon signals the ribosome to stop reading
  mRNA (stop UGA, UAA, UAG)

39
tRNA

• One region of tRNA bonds to a specific amino
  acid, the opposite loop contains a sequence of
  three bases called an anticodon
• tRNA anticodon bonds with the complementary mRNA
  codon

40
tRNA Structure
41

• Ribosome attaches to AUG start codon on mRNA
• AUG pairs with UAC on tRNA (UAC tRNA carries
  methionine)
• Ribosome moves along mRNA
• Codon paired with its anticodon (tRNA)
• Amino acid then added to the chain
• Continues until ribosome reaches a stop codon
• Several ribosomes translating same mRNA at same
  time
• mRNA is released, piece of protein is released

42
(No Transcript)
43
(No Transcript)