Topic 2.7 Replication, Transcription & Translationsciencestephenson.com/wp-content/uploads/2018/08/7-1-DNA-Replic… · Understandings U2: Helicase unwinds the double helix and separates

Topic 2.7 – Replication, Transcription & Translation

INTRO

IB BIO – 2.7 The central dogma of biology describes how information from DNA

is able to influence the traits of an organism. There are three

processes involved:

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2.7 – A – DNA Replication

INTRO

IB BIO – 2.7 In order for cells to reproduce and pass on genes, they must copy

their genome in a process called DNA replication. This occurs during

the S phase of the cell cycle.

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Understandings

U2: Helicase unwinds the double helix and separates the two strands by breaking hydrogen bonds.

Key Terms

Helicase

IB BIO – 2.7 In order for DNA to be replicated, the hydrogen bonds between the

two strands must be broken. This is done by an enzyme called

helicase, which exposes the nitrogenous bases.

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Understandings

U3: DNA polymerase links nucleotides together to form a new strand, using the pre-existing strand as a template.

Key Terms

DNA polymerase

IB BIO – 2.7 After the strands are separated, DNA polymerase links together

nucleotides complementary (A-T & C-G) to the original strands. This

results in two new DNA molecules identical to the original.

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Understandings

U1: The replication of DNA is semi-conservative and depends on complementary base pairing.

Key Terms

DNA Replication

Semi-conservative

Complementary

IB BIO – 2.7 7

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Because of complementary base pairing, the daughter DNA

molecules are identical to the original.

Each new strand consists of one newly-synthesized strand and one

strand inherited directly from the parent. This is known as being

semi-conservative.

Understandings

U1: The replication of DNA is semi-conservative and depends on complementary base pairing.

Key Terms

DNA Replication

Semi-conservative

Complementary

IB BIO – 2.7 8The model of replication was originally not well understood, so

there were three different models that were hypothesized.

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Semi-conservative Conservative Dispersive

Skills

S2: Analysis of Meselson and Stahl’s results to obtain support for the theory of semi-conservative replication of DNA.

Key Terms

Meselson & Stahl

IB BIO – 2.7 Meselson and Stahl designed

an experiment to determine

which model was accurate.

• First, they grew a culture of

bacteria in a broth

containing N15, a heavy

isotope of Nitrogen.

• As the bacteria divided,

they integrated the N15 into

their DNA, making it more

dense.

• Then they transferred the

bacteria to a broth with

only N14

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Skills


Key Terms

Centrifuge

IB BIO – 2.7 After set periods of time, they centrifuged samples of the bacteria.

This is technique used to used in an experiment to separate

substances by density. They expected one of following outcomes:

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Skills


Key Terms

Centrifuge

IB BIO – 2.7 After the bacteria had time to duplicate, they removed samples and

separated their DNA using centrifugation. The results they obtained

are shown here.

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Skills


Key Terms

Centrifuge

IB BIO – 2.7 After one generation, the N15 band had disappeared and a new

band between N15 and N14 appeared. This indicated that new

bacteria had 50% each of N15/N14 in their DNA.

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Skills


Key Terms

Centrifuge

IB BIO – 2.7 In successive generations, an N14-only band appeared and grew

darker while the N15/14 band remained.

This indicated that new DNA consisted of one parental strand and

one newly synthesized strand only containing N14.

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Skills


Key Terms

Meselsohn & Stahl

IB BIO – 2.7 Meselson’s and Stahl’s observation in their experiments led them

to conclude that the replication of DNA was a semi-conservative

process and that the other models were incorrect.

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https://upload.wikimedia.org/wikipedia/commons/thumb/f/fb/Meselson-stahl_experiment_diagram_en.svg

Applications

A1: Use of TaqDNA polymerase to produce multiple copies of DNA rapidly by the polymerase chain reaction (PCR).

Key Terms

PCR

IB BIO – 2.7 In order to study genes and use them in experiments, large

amounts must be obtained. A process called polymerase chain

reaction (PCR) uses DNA polymerase to do this.

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Applications


Key Terms

PCR

IB BIO – 2.7 In PCR reactions, all of the

components for DNA

replication are added to test

tubes, which are then put in

thermo-cyclers

Components include:

• Source DNA

• DNA Primers

• Free Nucleotides

• DNA Polymerase

• Reaction Buffer

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http://ib.bioninja.com.au/_Media/pcr-components_med.jpeg

Applications


Key Terms

PCR

IB BIO – 2.7 DNA primers are used to isolate a gene. These are short

strands of DNA that are complementary to regions on either side of

the sequence of interest.

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https://upload.wikimedia.org/wikipedia/commons/thumb/9/91/Primers_RevComp.svg

Applications


Key Terms

PCR

IB BIO – 2.7 The process of PCR involves stages of cycling temperatures:

• Denuturing – high temperature causes DNA strands to separate

• Annealing – lower temperature allows DNA primers to bind

• Extending – a medium temperature that is optimal for the Taq

DNA polymerase enzyme. This allows for effective replication.

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http://www.yourgenome.org/sites/default/files/illustrations/process/pcr_cycle_yourgenome.png

Applications


Key Terms

Taq DNA Polymerase

IB BIO – 2.7 The enzyme used in PCR is Taq DNA polymerase, which is isolated

from T. aquaticus. This bacteria is found in hot springs and so its

enzymes have high optimum temperatures.

Since PCR requires temperatures above body temperature, using

this enzyme is much more efficient than human DNA polymerase.

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Applications


Key Terms

PCR

IB BIO – 2.7 Each cycle of PCR doubles the copies of

the target gene. So, a large numbers of

copies can be produced in a short period

of time.

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REVIE

WIB BIO – 2.7 1. Discuss why DNA replication is important for

organisms.

2. Outline the role of helicase and DNA polymerase in

DNA replication.

3. Describe what is meant by the term semi-

conservative.

4. Analyze the findings of the Meselson-Stahl

experiment.

5. Outline the use of Tag DNA Polymerase in PCR.

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2.7 – B – Transcription

INTRO

IB BIO – 2.7 Before genes can be used to produce proteins, DNA must be

converted into RNA. This is done through transcription.

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Understandings

U4: Transcription is the synthesis of mRNA copied from the DNA base sequences by RNA polymerase.

Key Terms

Transcription

RNA Polymerase

IB BIO – 2.7 Transcripton is the process of creating mRNA copies from DNA

sequences. This is done by an enzyme called RNA polymerase.

To do this, a ‘bubble’ of DNA is opened and used as a template.

RNA polymerase then joins free-floating nucleotides complementary

to the DNA strand.

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Understandings


Key Terms

Transcription

Uracil

IB BIO – 2.7 25

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The RNA resulting from transciption has the same sequence as the

target DNA sequence. However, there are two significant

differences:

• RNA is single-

stranded while

DNA is double-

stranded

• RNA contains

uracil instead of

thymine

Understandings

S4: Deducing the DNA base sequence for the mRNA strand.

Key Terms

IB BIO – 2.7 Determine the RNA code that would be produced by the following

DNA sequences:

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Understandings

S4: Deducing the DNA base sequence for the mRNA strand.

Key Terms

IB BIO – 2.7 Determine the RNA code that would be produced by the following

DNA sequences:

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U A A U U C C G G C U A U C C U A U

C C G G U A A A U G C U A G U A C C

C C G G U U A A U U C C U U A U G A

Understandings


Key Terms

Transcription

mRNA

IB BIO – 2.7 28After transcription is complete,

the resulting RNA is called

messenger RNA (mRNA).

Replication and transcription

occur in the nucleus, however

proteins are made in the

cytoplasm.

So, the final mRNA molecules

leave the nucleus through holes

called nuclear pores.

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2.7 – C – Translation

Understandings

U5: Translation is

the synthesis of

polypeptides on

ribosomes.

Key Terms

Translation

IB BIO – 2.7 After transcription, mRNA

leaves the nucleus through

nuclear pores.

It travels to ribosomes, which

are the cell structures

responsible for synthesizing

polypeptide chains.

Ribosomes are the site of

translation.

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Understandings

U5: Translation is

the synthesis of

polypeptides on

ribosomes.

Key Terms

Translation

IB BIO – 2.7 During translation, ribosomes interpret the mRNA sequence and

synthesize polypeptide chains. The resulting proteins are typically

released into the cytoplasm or rough ER.

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Understandings

U6: The amino

acid sequence of

polypeptides is

determined by

mRNA according

to the genetic

code.

U7: Codons of

three bases on

mRNA correspond

to one amino acid

in a polypeptide.

Key Terms

Codon

IB BIO – 2.7 The sequence of amino acids in a polypeptide chain is determined

by the sequence of the mRNA nucleotides (A, U, C, G).

Every three bases of mRNA make up a codon. Each codon

corresponds to an amino acid determined by the genetic code.

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Understandings

U6: The amino

acid sequence of

polypeptides is

determined by

mRNA according

to the genetic

code.

U7: Codons of

three bases on

mRNA correspond

to one amino acid

in a polypeptide.

Key Terms

Genetic Code

IB BIO – 2.7 The genetic code is typically shown as a chart like the one below.

The bases of the codon correspond to an amino acid or a stop signal.

Some AA’s have multiple codons, while others only have one.

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Understandings

U8: Translation

depends on

complementary

base pairing

between codons

on mRNA and

anticodons on

tRNA.

Key Terms

tRNA

Codon

IB BIO – 2.7 During translation, the ribosome ‘reads’ each mRNA codon and

matches it with a tRNA molecule. Each tRNA has two distinct sites:

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1. An anticodon, which

is a three-base

sequence

complementary to

the codon.

2. An amino acid that

will be added to the

polypeptide chain.

Understandings

U8: Translation

depends on

complementary

base pairing

between codons

on mRNA and

anticodons on

tRNA.

Key Terms

IB BIO – 2.7 As the ribosome reads a mRNA strand, the AA’s on the tRNA’s are

bound via condensation to form a polypeptide chain.

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Skills

S1: Use a table of

the genetic code

to deduce which

codon(s)

corresponds to

which amino acid.

Key Terms

IB BIO – 2.7 Using an Amino Acid Table

1. Identify the three bases of the codon.

2. Find the first base on the left-hand side.

3. Find the second base on the top and identify the square where

they intersect.

4. Find the third base

on the right hand

side and identify

the amino acid for

the full codon.

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http://academic.pgcc.edu/~kroberts/Lecture/Chapter%207/07-11_GeneticCode_L.jpg

Skills

S1: Use a table of

the genetic code

to deduce which

codon(s)

corresponds to

which amino acid.

Key Terms

IB BIO – 2.7 37


Using an Amino Acid Table

Use the chart to determine what AA corresponds to:

- UAC - AAG - CUG - GAU - UAA

Skills

S1: Use a table of

the genetic code

to deduce which

codon(s)

corresponds to

which amino acid.

Key Terms

IB BIO – 2.7 38


Using an Amino Acid Table

Use the chart to determine what codons correspond to:

- Serine - Histidine - Valine - Arginine

Skills

S1: Use a table of

the genetic code

to deduce which

codon(s)

corresponds to

which amino acid.

Key Terms

IB BIO – 2.7 Using the chart, determine what codons correspond to:

• Serine:

- UCU, UCC, UCA, UCG, AGU, AGC

• Histidine:

- CAU, CAC

• Valine:

- GUU, GUC, GUA, GUG

• Arginine:

- CGU, CGC, CGA, CGG, AGA, AGG

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Skills

S3: Use a table of

mRNA codons and

their

corresponding

amino acids to

deduce the

sequence of

amino acids coded

by a short mRNA

strand of known

base sequence.

Key Terms

IB BIO – 2.7 Use an amino acid chart to determine the AA sequence of the

following mRNA chains.

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Skills

S3: Use a table of

mRNA codons and

their

corresponding

amino acids to

deduce the

sequence of

amino acids coded

by a short mRNA

strand of known

base sequence.

Key Terms

IB BIO – 2.7 Use an amino acid chart to determine the AA sequence of the

following mRNA chains.

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Met – Leu – Gly – Lys – Gln – Stop

Met – Phe – Lusc – Ala – Glu – Stop

Met – Arg – Ile – Phe – Arg – Stop

Applications

A2: Production of

human insulin in

bacteria as an

example of the

universality of the

genetic code

allowing gene

transfer between

species.

Key Terms

Insulin

IB BIO – 2.7 The same genetic code is used

by all organisms. So, the same

gene in one organism will

produce the same protein in

others.

Humans take advantage of this

in the production of insulin.

The human gene is inserted into

bacteria, which are then able to

produce insulin.

Large amounts of insulin-

producing bacteria are grown

and then the hormone is

harvested for human use.

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REVIE

WIB BIO – 2.7 1. Define translation.

2. Outline how the ribosome reads mRNA and

synthesis polypeptide chains.

3. Outline the structure of tRNA molecules.

4. Outline the steps needed to interpret mRNA with an

amino acid chart.

5. Explain the universality of the genetic code using

insulin as an example.

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Documents

Topic 2.7 Replication, Transcription & Translationsciencestephenson.com/wp-content/uploads/2018/08/7-1-DNA-Replic… · Understandings U2: Helicase unwinds the double helix and separates