CHAPTER 10 Molecular Biology of the Gene DNA serves as the molecular basis of heredity
Dec 22, 2015
CHAPTER 10Molecular Biology of the Gene
DNA serves as the molecular basis of heredity
The “Transforming Principle” 1928
Frederick Griffith Streptococcus pneumonia bacteria
was working to find cure for pneumonia
harmless live bacteria (“rough”) mixed with heat-killed pathogenic bacteria (“smooth”) causes fatal disease in mice
a substance passed from dead bacteria to live bacteria to change their phenotype
“Transforming Principle”
The “Transforming Principle”
Transformation = change in phenotypesomething in heat-killed bacteria could still transmit disease-causing properties
live pathogenicstrain of bacteria
live non-pathogenicstrain of bacteria
mice die mice live
heat-killed pathogenic bacteria
mix heat-killed pathogenic & non-pathogenicbacteria
mice live mice die
A. B. C. D.
DNA is the “Transforming Principle”
Avery, McCarty & MacLeod purified both DNA & proteins separately from
Streptococcus pneumonia bacteria which will transform non-pathogenic bacteria?
injected protein into bacteria no effect
injected DNA into bacteria transformed harmless bacteria into
virulent bacteria
1944
What’s theconclusion?
mice die
THE STRUCTURE OF THE GENETIC MATERIAL Experiments showed that DNA is the genetic material
The Hershey-Chase experiment showed that certain viruses reprogram host cells to produce more viruses by injecting their DNA
Confirmation of DNA
Hershey & Chaseclassic “blender” experimentworked with bacteriophage
viruses that infect bacteriagrew phage viruses in 2 media,
radioactively labeled with either 35S in their proteins 32P in their DNA
infected bacteria with labeled phages
1952 | 1969Hershey
Why useSulfurvs.Phosphorus?
Protein coat labeledwith 35S
DNA labeled with 32P
bacteriophages infectbacterial cells
T2 bacteriophagesare labeled withradioactive isotopesS vs. P
bacterial cells are agitatedto remove viral protein coats
35S radioactivityfound in the medium
32P radioactivity foundin the bacterial cells
Which radioactive marker is found inside the cell?
Which molecule carries viral genetic info?
Hershey & Chase
The Hershey-Chase Experiment
Blender experiment
Radioactive phage & bacteria in blender 35S phage
radioactive proteins stayed in supernatant therefore viral protein did NOT enter bacteria
32P phage radioactive DNA stayed in pellet therefore viral DNA did enter bacteria
Confirmed DNA is “transforming factor”
Taaa-Daaa!
Hershey & Chase
Alfred HersheyMartha Chase
1952 | 1969Hershey
DNA and RNA are polymers of nucleotides
The monomer unit of DNA and RNA is the nucleotide, containing
– Nitrogenous base– 5-carbon sugar– Phosphate group
Polynucleotide Sugar-phosphate backbone
Nucleotide Phosphategroup
Nitrogenous base(A, G, C, or T)
Sugar(deoxyribose)
DNA nucleotide
Thymine (T)
DNA has four kinds of bases, A, T, C, and G
Thymine (T) Cytosine (C) Adenine (A) Guanine (G)
Pyrimidines Purines
DNA and RNA are polymers of nucleotides
RNA has a slightly different sugar (RIBOSE) RNA has Uracil instead of Thymine
Phosphategroup
Nitrogenous base(A, G, C, or U)
Sugar(ribose)
Uracil (U)
Structure of DNA
James Watson and Francis Crick worked out the three-dimensional structure of DNA, based on work by Rosalind Franklin and Maurice Wilkens
1953 | 1962
Wilkins
Rosalind Franklin (1920-1958)
DNA Structure I
The structure of DNA consists of two polynucleotide strands wrapped around each other in a double helix
DNA Structure II
Hydrogen bonds between bases hold the strands together
Each base pairs with a complementary partner
A pairs with TG pairs with C
Paired bases
DNA structuredouble helix
2 sides like a ladder
Bases match together (A pairs with T
A : TC pairs with G
C : G
DNA Structure III
Three representations of DNA
Replication of DNA
Before a cell can divide by mitosis or meiosis, it must first make a copy of its chromosomes.
The DNA in the chromosomes is copied in a process called DNA replication.
Without DNA replication, new cells would have only half the DNA of their parents.
DNA is copied during interphase prior to mitosis and meiosis.
It is important that the new copies are exactly like the original molecules.
DNA Replication depends on specific base pairing
DNA replication follows a semiconservative model– The two DNA strands separate– Each strand is used as a pattern to produce a
complementary strand, using specific base pairing– Each new DNA helix has one old strand with one new
strand
Parental moleculeof DNA
Nucleotides
Both parental strands serveas templates
Two identical daughtermolecules of DNA
DNA REPLICATION II
Untwisting and replication of DNA
Copying DNA
Matching bases allows DNA to be easily copied
Making new DNA
Copying DNA replicationDNA starts as a double-stranded
moleculematching bases (A:T, C:G)
then it unzips…
DNA replication
DNA Helicase: enzyme responsible for uncoiling the double helix and unzipping the weak hydrogen bonds between the base pairs
DNA replication
DNA polymerase
Enzyme DNA polymerase adds new bases
DNA basesin nucleus
DNAPolymerase
Copying DNA Build daughter DNA
strand use original parent
strand as “template” add new matching
bases synthesis enzyme =
DNA polymerase
• Adding bases – can only add
nucleotides to 3 end of a growing DNA strand• need a “starter”
nucleotide to bond to
– strand only grows 53
DNAPolymerase III
DNAPolymerase III
DNAPolymerase III
DNAPolymerase III
energy
energy
energy
Replication energy
3
3
5
5
DNA replication begins at the origins of replication– DNA unwinds at the origin to produce a “bubble”
– Replication proceeds in both directions from the origin
– Replication ends when products from the bubbles merge with each other
DNA replication occurs in the 5’ 3’ direction– Replication is continuous on the 3’ 5’ template
– Replication is discontinuous on the 5’ 3’ template, forming short segments
10.5 DNA replication proceeds in two directions at many sites simultaneously
Copyright © 2009 Pearson Education, Inc.
DNA replication
• Leading strand- elongates as DNA unwinds
• Lagging strand –elongates in opposite direction . Synthesized discontinuously into small segments called Okazaki fragments
• DNA ligase (an enzyme)links these sections
Limits of DNA polymerase III can only build onto 3 end of an
existing DNA strand
Leading & Lagging strands
5
5
5
5
3
3
3
53
53 3
Leading strand
Lagging strand
Okazaki fragments
ligase
Okazaki
Leading strand continuous synthesis
Lagging strand Okazaki fragments joined by ligase
“spot welder” enzyme
DNA polymerase III
3
5
growing replication fork
New copies of DNA
Get 2 exact copies of DNA to split between new cells
DNA polymerase
DNA polymerase
Copied & Paired Up Chromosomes
centromere
2009-2010
Protein Synthesis Making Proteins
How does DNA code for cells & bodies? how are cells and bodies made from the
instructions in DNA
DNA Cells Bodies
DNA has the information to build proteins genes
DNA Proteins Cells Bodies
proteinscells
bodiesDNA gets all the glory,Proteins do all the work
cytoplasm
nucleus
Cell organization
DNADNA is in the nucleus
genes = instructions for making proteinswant to keep it there = protected
“locked in the vault”
Cell organization
Proteins chains of amino acids made by a “protein factory” in cytoplasm protein factory = ribosome
nucleus
cytoplasm
ribosome
aa
aa
aa
aa
aa
aa
aa
aaaa
aa
buildproteins
Passing on DNA information
Need to get DNA gene information from nucleus to cytoplasm need a copy of DNA messenger RNA
nucleus
cytoplasm
ribosome
mRNA
buildproteins
aa
aa
aa
aa
aa
aa
aa
aaaa
aa
mRNA
From nucleus to cytoplasm
DNA
transcription
nucleuscytoplasm
translation
trait
aa
aa
aa
aa
aa
aa
aa
aaaa
aa
protein
THE FLOW OF GENETIC INFORMATION FROM DNA TO RNA TO PROTEIN
The sequence of nucleotides in DNA provides a code for constructing a protein
– Protein construction requires a conversion of a nucleotide sequence to an amino acid sequence
– Transcription rewrites the DNA code into RNA, using the same nucleotide “language”
– Translation involves switching from the nucleotide “language” to amino acid “language”
DNA -> RNA -> protein.
Protein Synthesis: 2 step process
1. TRANSCRIPTION In nucleus ~ DNA -> mRNA2. TRANSLATION
in cytoplasm ~ mRNA -> ProteinInvolves 3 types of RNA1. Messenger RNA (mRNA) =carries the blueprint for construction of a protein2. Ribosomal RNA (rRNA) = the construction site where the protein is made3. Transfer RNA (tRNA) = the truck delivering the proper amino acid to the
site at the right time
10.7 Genetic information written in codons is translated into amino acid sequences
Transfer of DNA to mRNA uses “language” of nucleotidesLetters: nitrogen bases of nucleotides
(A,T,G,C)Words: codons ~triplets of bases ( ex. AGC)Sentences: polypeptide chainThe codons in a gene specify the amino
acid sequence of a polypeptide
10.8 The genetic code is the Rosetta stone of life
– Redundant: More than one codon for some amino acids
– Unambiguous: Any codon for one amino acid does not code for any other amino acid
– Does not contain spacers or punctuation: Codons are adjacent to each other with no gaps in between
– Nearly universal
10.9 Transcription produces genetic messages in the form of RNA
In transcription, the DNA helix unzips RNA nucleotides
line up along one strand of the DNA following the base-pairing rules
The single-stranded messenger RNA peels away and the DNA strands rejoin
Transcription
Making mRNA from DNADNA strand is the
template (pattern)match bases
U : AG : C
EnzymeRNA polymerase
Matching bases of DNA & RNA
Double stranded DNA unzips
A G GGGGGT T A C A C T T T T TC C C CA A
Matching bases of DNA & RNA
Double stranded DNA unzips
A G GGGGGT T A C A C T T T T TC C C CA A
Matching bases of DNA & RNA
Match RNA bases to DNA bases on one of the DNA strands
U
A G GGGGGT T A C A C T T T T TC C C CA A
U
UU
U
U
G
G
A
A
A C CRNA polymerase
C
C
C
C
C
G
G
G
G
A
A
A
AA
Matching bases of DNA & RNA
U instead of T is matched to A
TACGCACATTTACGTACGCGGDNA
AUGCGUGUAAAUGCAUGCGCCmRNAaa
aa
aa
aa
aa
aa
aa
aaaa
aa
U C CCCCCA A U G U G A A A A AG G G GU Uribosome
aa
aa
aa
aa
aa
aa
aa
aaaa
aa
protein
cytoplasm
nucleus
traitU C CCCCCA A U G U G A A A A AG G G GU U
ribosome
10.10 Eukaryotic RNA is processed before leaving the nucleus
Noncoding segments called introns are spliced out ( coding segment = exons)
A 5’ cap and a poly A tail are added to the ends
10.11 Transfer RNA molecules serve as interpreters during translation
In the cytoplasm, a ribosome attaches to the mRNA and translates its message into a polypeptide
The process is aided by transfer RNAs
Each tRNA molecule has a triplet anticodon on one end and an amino acid attachment site on the other
Anticodon base pairs with codon of mRNA
10.12 Ribosomes build polypeptides
Translation occurs on the surface of the ribosome
– Ribosomes have two subunits: small and large
– Ribosomal subunits come together during translation
– Ribosomes have binding sites for mRNA and tRNAs
aa
aa
aa
aa
aa
aa
aa
aaaa
aa
protein
cytoplasm
nucleus
traitU C CCCCCA A U G U G A A A A AG G G GU U
ribosome
How does mRNA code for proteins
mRNA leaves nucleusmRNA goes to ribosomes in cytoplasmProteins built from instructions on mRNA
aa aa aa aa aa aa aa aa
How?
mRNA
U C CCCCCA A U G U G A A A A AG G G GU U
How does mRNA code for proteins?
TACGCACATTTACGTACGCGGDNA
AUGCGUGUAAAUGCAUGCGCCmRNA
Met ArgVal Asn Ala Cys Alaprotein
?
How can you code for 20 amino acids withonly 4 DNA bases (A,U,G,C)?
ribosome
aa aa aa aa aa aa aa aa
AUGCGUGUAAAUGCAUGCGCCmRNA
mRNA codes for proteins in triplets
TACGCACATTTACGTACGCGGDNA
AUGGUAAAUGCAUGCGCCmRNA
Met Arg Val Asn Ala Cys Alaprotein
?
Codon = block of 3 mRNA bases
codon
ribosome
For ALL life! strongest support for a
common origin for all life
Code has duplicates several codons for
each amino acid mutation insurance!
Start codon AUG methionine
Stop codons UGA, UAA, UAG
The mRNA code
How are the codons matched to amino acids?
TACGCACATTTACGTACGCGGDNA
AUGCGUGUAAAUGCAUGCGCCmRNA
anti-codon
codon
tRNAUAC
MetGCA
ArgCAU
Val Anti-codon = block of 3 tRNA bases
aminoacid
mRNA to protein = Translation
The working instructions mRNAThe reader ribosomeThe transporter transfer RNA (tRNA)
mRNAU C CCCCCA A U G U G A A A A AG G G GU U
aaaa
aa
tRNA
GGU
aa
tRNA
U A C
aa
tRNA
GA C
tRNA
aa
A GU
ribosome
aa
aa
aaaa
aa
aa
aa
mRNA
From gene to protein
DNA
transcription
nucleuscytoplasm
protein
translation
trait
U C CCCCCA A U G U G A A A A AG G G GU Uribosome
tRNA
aa
protein
aa
aa
aa
aa
aa
aa
aa
aaaa
aa
aa
transcription
cytoplasm
nucleus
translation
trait
From gene to protein
transcriptiontranscription
translationtranslation
proteinprotein
10.15 Review: The flow of genetic information in the cell is DNARNAprotein
The sequence of codons in DNA spells out the primary structure of a polypeptide Polypeptides form
proteins that cells and organisms use
Process of protein synthesis
DNA
Transcribed strand
Transcription
Translation
RNA
Polypeptide
Startcodon
Stopcodon
10.16 Mutations can change the meaning of genes
Mutations are changes in the DNA base sequence These are caused by errors in DNA replication or by
mutagens The change of a single DNA nucleotide causes sickle-
cell disease
Mutations Any change in DNA sequence is called a mutation. can be caused by errors in replication, transcription,
cell division, or by external agents.
If mutation occurs in gametes (sex cells) it will be passed on to offspring
may produce a new trait or it may result in a protein that does not work correctly.
the mutation results in a protein that is nonfunctional, and the embryo may not survive
In some rare cases a gene mutation may have positive effects.
Mutations
If mutation takes place in a body cell, it is not passed on to organism’s offspring Damage to a gene may impair the function of the
cell When that cell divides, the new cells also will have
the same mutation Some mutations of DNA in body cells affect genes
that control cell division. This can result in the cells growing and dividing
rapidly, producing cancer.
Types of mutations
Changes to the letters (A,C,T,G bases) in the DNApoint mutation
change to ONE letter (base) in the DNAmay cause change to protein, may not
frameshift mutationaddition of a new letter (base) in the DNA
sequencedeletion of a letter (base) in the DNAboth of these shift the DNA so it changes how the
codons are readbig changes to protein!
Mutations
Point mutationssingle base change
silent mutation no amino acid change redundancy in code
missense change amino acid
nonsense change to stop codon
Mutations
Frameshift shift in the reading
framechanges everything
“downstream” insertions
adding base(s)deletions
losing base(s)
Where would this mutation cause the most change:beginning or end of gene?
THERAATANDTHECATATETHEREDBATTHERAATANDTHECATATETHEREDBAT
Frameshift mutations
THERATANDTHECATATETHEREDBAT
THERTANDTHECATATETHEREDBAT
THERATANDTHECATATETHEREDBAT
THERTANDTHECATATETHEREDBAT
Deletion
Insertion
Causes of Mutations
sometimes a mistake in base pairing during DNA replication.
many mutations are caused by factors in the environment
Any agent that can cause a change in DNA is called a mutagen. Mutagens include radiation, chemicals, and even
high temperatures