Topic 2.6 Structure of DNA and RNA - PowerPoint Presentation

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Topic 2.6 Structure of DNA and RNA

Essential idea:

The structure of DNA allows efficient storage of genetic information.

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2.6 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

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2.6.1 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

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S 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

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U 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

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U 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’

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U 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

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A 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.

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Random 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!

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Topic 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.

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2.7 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

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U 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

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Meselson 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,

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N, which became incorporated into bases of the bacterial DNA. Provided evidence demonstrating semi-conservative replication.

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DNA Replication is Semiconservative

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U 2.7.2 Helicase unwinds the double helix and separates the two strands by breaking hydrogen bonds

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U 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

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U 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

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Transcription

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

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U 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

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U 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

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U 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

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U 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

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Termination

When a stop codon is reached, the release factor enters

The release factor will add water instead of an amino acid

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U 2.7.6 The amino acids sequence of polypeptides is determined by mRNA according to the genetic code

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S 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

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Polymerase 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

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A 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

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A 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