IB Biology Miss Werba 2 J WERBA IB BIOLOGY AHL TOPIC 7 NUCLEIC ACIDS AND PROTEINS THINGS TO COVER Direction of transcription Sense and antisense strands of DNA Prokaryotic transcription ID: 909059
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Slide1
TRANSCRIPTION
AHL Topic 7.3
IB Biology
Miss
Werba
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J WERBA – IB BIOLOGY
AHL TOPIC 7 –
NUCLEIC ACIDS AND PROTEINS
Slide3THINGS TO COVERDirection of transcriptionSense and antisense strands of DNAProkaryotic transcription:
promoter region, RNA polymerase,
NTPs & the terminator
Eukaryotic transcription
J WERBA – IB BIOLOGY
3
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J WERBA – IB BIOLOGY
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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J WERBA – IB BIOLOGY
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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J WERBA – IB BIOLOGY
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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J WERBA – IB BIOLOGY
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;
8
max