Essential idea The structure of DNA allows efficient storage of genetic information 26 Structure of DNA and RNA Nature of science Using models as representation of the real worldCrick and Watson used model making to discover the structure of DNA 110 ID: 909066
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Slide1
Topic 2.6 Structure of DNA and RNA
Essential idea:
The structure of DNA allows efficient storage of genetic information.
Slide22.6 Structure of DNA and RNA
Nature
of science:
Using
models as representation of the real world—Crick and Watson used model making to discover the structure of DNA. (1.10)
Understandings
The nucleic acids DNA and RNA are polymers of nucleotides
DNA differs from RNA in the number of strands present, the base composition and the type of pentose
DNA is a double helix made of two antiparallel strands of nucleotides linked by hydrogen bonding between complementary base pairs
Applications and Skills
Application
: Crick and Watson’s elucidation of the structure of DNA using model making
Skill
: Drawing simple diagrams of the structure of single nucleotides of DNA and RNA, using circles, pentagons and rectangles to represent phosphates,
pentoses
, and bases
Slide32.6.1 The nucleic acids DNA and RNA are polymers of nucleotides
What does
DNA
stand for?
Deoxy
ribonucleic acid
What does
RNA
stand for?
Ribonucleic acid
DNA and RNA are composed of
nucleotides
What are the three parts of a nucleotide?
Pentose sugar
Phosphate group
Nitrogenous base
Slide4S 2.6.1: Drawing simple diagrams of the structure of single nucleotides of DNA and RNA, using circles, pentagons and rectangles to represent phosphates,
pentoses
, and bases
Slide5U 2.6.3 DNA is a double helix made of two antiparallel strands of nucleotides linked by hydrogen bonding between complementary base
pairs
What are the 4 nitrogenous based of
DNA
?
Adenine (A), Thymine (T), Cytosine (C), Guanine (G)
Which ones are
pyrimidines
?
Cytosine and thymine
Which ones are purines?Adenine and guanineWhat does Adenine (A) pair with?Thymine (T)What does Guanine (G) pair with?Cytosine (C)This is called complementary base pairing or Chargaff’s ruleEasy way to remember GCAT
Pure
A
s Gold
Pyrimidines=
CUT
Slide6U 2.6.3
What shape is DNA?
DNA is a
double stranded helix
It is composed of a
sugar phosphate backbone
and
nucleotide rungs
like a ladder
What types of bonds hold the sugar phosphate backbone together?
Covalent bondsWhat type of bonds hold the nucleotides together?Hydrogen bond (3 bonds between G and C and 2 bonds between A and T)Does DNA run parallel or antiparallel?Antiparallel What direction does DNA run?5’ to 3’
Slide7Slide8U 2.6.2 DNA differs from RNA in the number of strands present, the base composition,
and the type of pentose
What are three difference between DNA and RNA?
DNA contains
deoxyribose
sugar and RNA contains
ribose
sugar
DNA is
double
stranded and RNA is single strandedDNA contains thymine and RNA contains uracilSo in RNA Adenine pairs with Uracil
Slide9Slide10A 2.6.1 Crick and Watson’s elucidation of the structure of DNA using model making
In the 1950s the race to find the structure of DNA was on.
Many scientists were working to discover what the shape of DNA might look like. With the discovery by Chargaff of the base-pairing nature of nucleic acids and Pauling’s work on protein structure, Francis Crick and James Watson were intrigued in deducing the structure of DNA.
Who’s experimental data did Crick and Watson use to help elucidate the structure of DNA?
Rosalind Franklin and Wilkins
While Franklin and Wilkins took an experimental approach, Watson and Crick took a physical approach at Cambridge University using models. After attending a lecture by Franklin they tried to use her data to construct a model using cardboard cut outs in the labs. This model failed and their research came to a stop. When Franklin discovered the x-ray crystallography of the DNA molecule Watson and Crick were able to use this data to begin construction of the DNA molecule again in 1953.
Slide11Slide12Random DNA facts!
1 gram of DNA is capable of holding 700 Terabytes of data
8% of the human genome is actually made of ancient virus DNA
If you unwound all DNA molecules in a human body and place them end to end, the total length would be long enough for a trip from Earth to Pluto and back to Earth
Thank you Bio-Rad!
Slide13Topic 2.7 DNA replication, transcription, and translation
Essential Idea:
Genetic information in DNA can be accurately copied and can be translated to make the proteins needed by the cell.
Slide142.7 DNA replication, transcription, and translation
Nature
of science:
Obtaining
evidence for scientific theories—Meselson and Stahl obtained evidence for the semi-conservative replication of DNA. (1.8)
Understandings
The replication of DNA is semi-conservative and depends on complementary base pairing
Helicase unwinds the double helix and separates the two strands by breaking hydrogen bonds
DNA polymerase links nucleotides together to form a new strand, using the pre-existing strand as a template
Transcription is the synthesis of mRNA copied from the DNA base sequences by RNA polymerase
Translation is the synthesis of polypeptides on ribosomesThe amino acids sequence of polypeptides is determined by mRNA according to the genetic codeCodons of three bases on mRNA correspond to one amino acid in a polypeptideTranslation depends on complementary base pairing between codons on mRNA and anticodons on tRNA
Applications and skillsApplication: Use of Taq DNA polymerase to produce multiple copies of DNA rapidly by the polymerase chain reaction (PCR)Application
: Production of human insulin in bacteria as an example of the universality of the genetic code allowing gene transfer between speciesSkill: Use a table of the genetic code to deduce which codon(s) correspond to which amino acid
Slide15U 2.7.1 The replication of DNA is semi-conservative and depends on complementary base
pairing
What is
semi-conservative replication
?
The two strands of DNA are separated by breaking hydrogen bond between the base pairs
New nucleotides are added to the template strand by the base pair rule
So one strand is old DNA and one strand is new
Slide16Meselson and Stahl Experiment
Proposed that DNA replication is semi-conservative. This means that each of the two daughter molecules produced through replication will have one old or conserved strand from the parent molecule and one newly created strand.
Meselson and Stahl (1958) of Cal Tech grew bacteria in a medium containing the heavy isotope of nitrogen,
15
N, which became incorporated into bases of the bacterial DNA. Provided evidence demonstrating semi-conservative replication.
Slide17DNA Replication is Semiconservative
Slide18Slide19U 2.7.2 Helicase unwinds the double helix and separates the two strands by breaking hydrogen bonds
Slide20U 2.7.3 DNA polymerase links nucleotides together to form a new strand, using the pre-existing strand as a template
Helicase
unwinds the DNA strand by breaking hydrogen bonds
What enzyme added complementary base pairs?
DNA polymerase III
will add the complementary base pairs using the pre-existing DNA strand as a template
A-T and G-C and visa versa T-A and C-G
The two daughter DNA molecules are identical because of complementary base pairing
Note
: Remember HL we go into more detail in Topic 7
Slide21U 2.7.4 Transcription is the synthesis of mRNA copied from the DNA base sequences by RNA
polymerase
What is
transcription
?
DNA
mRNA
Copying of the base sequence of a gene in DNA to messenger RNA to ultimately make a protein/polypeptide
One strand of DNA will be used as a template for making the mRNA
Antisense strand
The strand not used as a template is called the sense strandWhere does this occur in a eukaryotic cell?Nucleus
Slide22Transcription
RNA polymerase II
opens the DNA strand
RNA polymerase added the complementary base pairs to the new strand of mRNA except
uracil (U)
replaces thymine (T)
So A-U and G-C
The RNA nucleotides are linked by
covalent
bonds
The RNA strand separates from the DNA strand and is released DNA strand recoils
Slide23U 2.7.5 Translation is the synthesis of polypeptides on ribosomes
What is
translation
?
mRNA
protein/polypeptide
Where does this occur in a eukaryotic cell?
Cytoplasm
The amino acid sequence of the polypeptide is determined by mRNA according to the genetic code
The genetic code is a triplet code and nucleotides are read in groups of three, what are they called?
These are called codonsmRNA, tRNA, ribosomes
Slide24U 2.7.7 Codons of three bases on mRNA correspond to one amino acid in a polypeptide
Initiation
mRNA binds to small subunit of the ribosome
What is the start codon?
AUG or methionine
Slide25U 2.7.8 Translation depends on complementary base pairing between codons on mRNA and anticodons on
tRNA
Transfer RNA (
tRNA
) molecules contain an anticodon, what is an
anticodon
?
Triplet code that matches the
codon
tRNA
also carries the matching amino acid
Slide26U 2.7.6 The amino acids sequence of polypeptides is determined by mRNA according to the genetic code
Elongation
tRNA
enter at the A site
A dipeptide bond will form between the
tRNA
at the P site and the
tRNA
in the A site
The ribosome will move down along the mRNA strand
The tRNA in the P site detachesThe tRNA that was in the A site is now in the P site allowing for another tRNA to enter
Slide27Termination
When a stop codon is reached, the release factor enters
The release factor will add water instead of an amino acid
Slide28U 2.7.6 The amino acids sequence of polypeptides is determined by mRNA according to the genetic code
Slide29S 2.7.1 Use a table of the genetic code to deduce which codon(s) correspond to which amino acid
The
genetic code
is a triplet code
4
2
= 16 codons which is not enough for 20 amino acids
4
3
= 64 codons for 20 amino acids
Three stop codonsUAA, UAG, UGAAUG-GCC-CAU-UCU-GGG-UGAMet-Ala-His-Ser-Gly-STOP
Slide30Polymerase Chain Reaction (PCR)
What is
PCR
used for?
C
an be used to amplify specific sections of DNA
A
thermocycler
is used to amplify the DNA
How do we amplify the DNA?
Series of annealing and coolingTo amplify a section of DNA specific components are needed:DNA template- strand of DNA where region is locatedForward primer
- going in the direction of the DNA regionReverse primer- going in the opposite direction of the DNA region
Taq polymerase- added nucleotides
dNTPs- nucleotides to construct new DNA strandsBuffer- to make everyone happyIons
- depending on what scientist wants to accomplish
Slide31A 2.7.1 Use of
Taq
DNA polymerase to produce multiple copies of DNA rapidly by the polymerase chain reaction (PCR
)
What is
Taq
polyermase
?
Taq
polymerase is a thermostable DNA polymeraseIt was isolated from the bacterium Thermus aquaticus which lives in hot spring and hydrothermal ventsWhy is Taq polyermase a good enzyme to use in PCR?
We use Taq polymerase in PCR reactions because the enzyme can survive the high temperatures during the denaturing cycle
Slide32Slide33A 2.7.2 Production of human insulin in bacteria as an example of the universality of the genetic code allowing gene transfer between
species
The genetic code is
universal
What does this mean?
This same code for amino acids is used in different organisms
Example:
E. coli
and humans use the same genetic code
Explain the universality of the genetic code in regard to insulin
Gene for insulin can be transferred from humans into E. coli to produce insulin to treat diabetesSome variations of the genetic codeCUG in yeast codes for serine instead of leucineIn some organisms a stop codon is used for a non-standard amino acid