1. TRANSCRIPTION & TRANSLATION
Topic 3.5
IB Biology
Miss Werba

2. CARBS, LIPIDS & PROTEINS 3.5 TRANSCRIPTION & TRANSLATION
TOPIC 3 - BIOCHEMISTRY
3.1 ELEMENTS & WATER
3.2
CARBS, LIPIDS & PROTEINS
3.3
DNA STRUCTURE
3.4
DNA REPLICATION
3.5 TRANSCRIPTION & TRANSLATION
3.6 ENZYMES
3.7 CELL RESPIRATION
3.8 PHOTOSYNTHESIS
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3. THINGS TO COVER Structure of DNA vs RNA Process of transcription
Codons
Process of translation
Relationship between one gene and one polypeptide
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4. COMPARING DNA & RNA DNA = DEOXYRIBONUCLEIC ACID
DNA is found in the nucleus
DNA is made up of nucleotides
Each nucleotide consists of:
a nitrogenous base  T, C, A or G
a pentose sugar  deoxyribose
a phosphate group
There are four DNA nucleotides
It is double stranded and twisted into a double helix A T C G D

5. COMPARING DNA & RNA RNA = RIBONUCLEIC ACID
RNA is found both inside and outside of the nucleus
RNA is also made up of nucleotides
Each nucleotide consists of:
a nitrogenous base  U, C, A or G
a pentose sugar  ribose
a phosphate group
There are four RNA nucleotides
It is single stranded and therefore linear A U C G R

6. COMPARING DNA & RNA FEATURE DNA RNA Number of strands 2 strands
3.5.1
COMPARING DNA & RNA
FEATURE
DNA
RNA
Number of strands
2 strands
1 strand
Sugar
deoxyribose
ribose
Bases
A=T C≡G
Nucleotides may contain T
A=U C≡G
Nucleotides may contain U
Shape
Double helix
Linear
Check whether question is asking for differences between molecules or nucleotides. You cannot say that a nucleotide is double stranded!
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7. COMPARING DNA & RNA Base pairing
RNA is used to copy the coded information from the DNA so that it can utilised by the cell.
This occurs for two reasons:
So that the DNA remains protected within the nucleus and doesn’t get damaged whenever it is used
The DNA is too big to fit through the nuclear pores (gaps) in the membrane surrounding the nucleus, while RNA is small.
DNA and RNA both follow Chargaff’s base pairing rule
HOWEVER, in RNA, Uracil pairs with Adenine (instead of Thymine)

8. COMPARING DNA & RNA Base pairingU T D R

9. TYPES OF RNA – bonus  Messenger RNA (mRNA)
3.5
TYPES OF RNA – bonus 
Messenger RNA (mRNA)
Copy of gene for translation
Transfer RNA (tRNA)
Brings amino acid to ribosome
Ribosomal RNA (rRNA)
Catalytic part of the ribosome
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10. 3.5.2
DNA TRANSCRIPTION
Definition: Process of making an RNA copy of a DNA sequence (gene)
Location: nucleus
Requires: DNA, RNA nucleotides, RNA polymerase, ATP
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11. 3.5.2
DNA TRANSCRIPTION
RNA polymerase binds to a promoter sequence and separates the DNA strands
RNA nucleotides (ribonucleotides) are brought in to pair with the exposed DNA bases.
The complementary base pairing rule is followed:
An exposed C base  G base will be brought in
An exposed G base  C base will be brought in
An exposed T base  A base will be brought in
An exposed A base  U base will be brought in
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12. 3.5.2
DNA TRANSCRIPTION
RNA polymerase joins the RNA nucleotides together with covalent bonds
The transcription process stops when a termination sequence is reached
The mRNA then leaves the nucleus and heads to the cytoplasm through the nuclear pores.
Transcription is necessary b/c:
DNA is too precious to be moved all the time
DNA is too big to exit through the pores
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13. TRANSCRIPTION Copying the code
Control-click on the picture to follow the hyperlink!

14. THE GENETIC CODE Codons:
3.5.3
THE GENETIC CODE
Codons:
Triplet of bases on the mRNA which encodes a particular amino acid
There are 4 bases  therefore 43 =64 combinations
The order of the codons determines the amino acid sequence for a protein
The coding region always starts with a START codon (AUG) and terminates with a STOP codon
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15. 3.5.3
THE GENETIC CODE
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16. THE GENETIC CODE Features of the genetic code: Universality
3.5.3
THE GENETIC CODE
Features of the genetic code:
Universality
(Almost) every living thing uses the same code
Degeneracy
Multiple codons may code for one amino acid
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17. 3.5.4
DNA TRANSLATION
Definition: Process of protein synthesis in which the genetic information encoded in mRNA is translated into a sequence of amino acids in a polypeptide chain
Location: cytoplasm (at ribosomes)
Requires: mRNA, ribosome, tRNA, amino acids, ATP
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18. 3.5.2
DNA TRANSLATION
Remember: MR CATAP (mRNA, ribosome, codon, anticodon, tRNA, amino acid, polypeptide)
mRNA binds to a ribosome which initiates translation
The mRNA is read in codons (from start codon = AUG)
Anticodons on tRNA align opposite appropriate codons (according to complementary base pairing)
tRNA brings amino acids to the ribosome (according to the genetic code)
Ribosomes join amino acids together with peptide bonds
When a stop codon is reached translation stops and a polypeptide chain is released
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19. 3.5.4
DNA TRANSLATION
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20. ONE GENE, ONE POLYPEPTIDE
3.5.5
ONE GENE, ONE POLYPEPTIDE
Gene: a segment of DNA coding for a polypeptide
Proteins may be made up of multiple polypeptides and therefore can be made from multiple genes (e.g. haemoglobin)
One gene gives rise to one polypeptide!
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21. TRANSLATION Building the protein
Control-click on the picture to follow the hyperlink!

23. Sample questions
Q1. What sequence of processes is carried out by the structure labeled X during translation?
Combining with an amino acid and then binding to an anticodon
Binding to an anticodon and then combining with an amino acid
Binding to a codon and then combining with an amino acid
Combining with an amino acid and then binding to a codon
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24. Sample questions
A1. D
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25. Sample questions
Q2. Explain the significance of complementary base pairing for replication, transcription and translation.
(8 marks)
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26. Sample questions A2. A-T and C-G in DNA; A-U and C-G in RNA;
complementary base pairing in replication ensures identical nucleotide sequence of new complementary strands;
semi-conservative replication;
transcription produces RNA sequence complementary to the DNA sequence (of the gene);
triplets of nucleotides on mRNA are codons;
translation converts mRNA sequence of information into a specific amino acid chain (polypeptide);
(each class of) tRNA carries a specific triplet of (three) bases called an anticodon;
anticodons bind to codons by complementary base pairing;
(each class of) tRNA with specific complementary anticodons carry specific amino acids;
sequence of mRNA codons translates into specific amino acid sequence;
enables conservation of information transfer from DNA to RNA to polypeptide;
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