TRANSCRIPTION AHL Topic 7.3 - PowerPoint Presentation

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TRANSCRIPTION

AHL Topic 7.3

IB Biology

Miss

Werba

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J WERBA – IB BIOLOGY

AHL TOPIC 7 –

NUCLEIC ACIDS AND PROTEINS

THINGS TO COVERDirection of transcriptionSense and antisense strands of DNAProkaryotic transcription:

promoter region, RNA polymerase,

NTPs & the terminator

Eukaryotic transcription

J WERBA – IB BIOLOGY

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DIRECTION OF TRANSCRIPTION

Command term =

STATE

Transcription is carried out in a 5’→ 3’ direction.

This means the 5’ end of the RNA strandThe 5’ end of the free RNA nucleotide is added to the

3’ end of the RNA molecule

that is already synthesized.

Addition of nucleotides

is catalysed by

RNA polymerase

.

7.3.1

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SENSE and ANTISENSE STRANDS

Command term =

DISTINGUISH

Sense strand:

the coding strand of DNA - ie. it contains the genesnot transcribed

!

Antisense strand:

also known as the

template strand

complementary

to the sense strand

transcribed into mRNA

Why?

By transcribing the antisense strand, the

base sequence of the mRNA will be the same as the coding DNA

(except U replace T)

7.3.2

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PROKARYOTIC TRANSCRIPTION

Command term =

EXPLAIN

Transcription in prokaryotes involves a number of elements:

A promoter regionAttachment of ribonucleoside

triphosphates

RNA polymerase

A

terminator

region

7.3.3

Ref: IB Biology, Oxford Study Courses

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PROKARYOTIC DNA REPLICATION

Command term =

EXPLAIN

1) The promoter region

The promoter region is found on the sense strandSpecific sequence of DNA bases that acts as a binding point for RNA polymeraseRNA polymerase unwinds small sections of DNA

7.2.2

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PROKARYOTIC DNA REPLICATION

Command term =

EXPLAIN

2)

Ribonucleoside triphosphates & RNA polymeraseRNA polymerase adds

ribonucleoside

triphosphates

to the

DNA antisense strand

using complementary base pairing

NTPs are added to the

3’ end

of the RNA strand.

This forms

messenger RNA (mRNA)

7.2.2

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PROKARYOTIC DNA REPLICATION

Command term =

EXPLAIN

3) The terminator region

The terminator region is also found on the sense strandSpecific sequence of DNA bases that acts as an end point for transcriptionRNA polymerase breaks free and the mRNA strand is released

7.2.2

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EUKARYOTIC TRANSCRIPTION

Command term =

STATE

Eukaryotic RNA needs the removal of

introns to form mature mRNA.Eukaryotic pre-mRNA contains exons

and

introns

Remember:

exons

stay in,

introns

move out

Introns

are transcribed but not translated

Introns

need to be

removed

before translation using

splicing enzymes

This will form

mature mRNA

, ready for translation.

7.3.4

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Sample questions

Q1.

Where does the RNA polymerase bind during the process of transcription

?

The polysome

The operator

The promoter

The initiator

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Sample questions

Q2.

The sequence of nucleotides in a section of RNA is:

GCCAUACGAUCG What is the base sequence of the DNA sense strand?

CGGUAUGCUAGC

GCCATACGATCG

CGGTATGCTAGC

GCCAUACGAUCG

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Sample questions

Q3.

Explain the process of transcription leading to the formation of mRNA

. [8]

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Sample questions

A1.

C

A2. B

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Sample questions

A3.

RNA polymerase

; (polymerase number is not required)

binds to a promoter on the DNA;unwinding the DNA strands;binding nucleoside triphosphates

;

to the antisense strand of DNA;

as it moves along in a 5′→3′ direction;

using complementary pairing/A-U and C-G;

losing two phosphates to gain the required energy;

until a terminator signal is reached (in prokaryotes);

RNA detaches from the template and DNA rewinds;

RNA polymerase detaches from the DNA;

many RNA polymerases can follow each other;

introns

have to be removed in eukaryotes to form mature mRNA;

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