IB Topics: DNA, Transcription, Translation

(3.3, 3.4, 3.5)

7.1, 7.2, 7.3, 7.4

7.1 DNA Structure

7.1.1 Describe the structure of DNA, including the

7.1.2 Outline the structure of nucleosomes.

7.1.3 State that nucleosomes help to supercoil chromosomes and help to regulate transcription.

7.1.4 Distinguish between unique or single-copy genes & highly repetitive sequences in nuclear DNA.

7.1.5 State that eukaryotic genes can contain exons and introns.

Living organisms use DNA as their genetic material. Explain how DNA is replicated within the cells of living organisms.

(Total 8 marks)

Happy Tuesday!! 8/28

• helix is unwound;• two strands are separated;• helicase (is the enzyme that unwinds the helix separating the two strands);• by breaking hydrogen bonds between bases;• new strands formed on each of the two single strands;• nucleotides added to form new strands;• complementary base pairing;• A to T and G to C;• DNA polymerase forms the new complementary strands;• replication is semi-conservative;• each of the DNA molecules formed has one old and one new strand;• [8]

7.2 DNA Replication

7.2.1 State that DNA replication occurs in a 5  3 direction.

7.2.2 Explain the process of DNA replication in prokaryotes, including the role of enzymes

7.2.2 Explain the process of DNA replication in prokaryotes, including the role of enzymes

IB Book, fig 7.7 page 200

• Examiner’s Hint– Draw the figure from memory– Annotate what’s happening at specific

locations

7.2.3 State that DNA replication is initiated at many points in eukaryotic chromosomes.

Primer

Primer

LIFE book

Sure Happy It’s Thursday, 8/30Sure Happy It’s Thursday, 8/30

• Explain the process of transcription in Explain the process of transcription in eukaryotes.eukaryotes.

• (8)(8)

• RNA polymerase controls transcription / is the enzyme used in transcription;• DNA is unwound by RNA polymerase;• DNA is split into two strands;• mRNA is made by transcription;• promoter region (by start of gene) causes RNA polymerase to bind;• anti-sense / template strand of DNA is transcribed;• direction of transcription is ;• free nucleotide triphosphates used;• complementary base pairing between template strand and RNA

nucleotides / bases;• Accept this marking point if illustrated using a diagram• RNA contains uracil instead of thymine;• terminator (sequence) stops RNA polymerase / transcription;• mRNA is released / RNA polymerase released; 8 max

• List three of the other molecules, apart from mRNA, required for transcription.

• 3 mks

• DNA;• RNA polymerase;• (ribose) nucleotides / ribonucleotides / RNA

nucleotides;• transcription factors;• nucleoside / ribonucleoside triphosphates; 3

max• Any two of the following: A / C / G / U;

7.3 Transcription

7.3.1 State that transcription is carried out in a 5  3 direction.

7.3.2 Distinguish between the sense & antisense strands of DNA.

7.3.3 Explain the process of transcription in prokaryotes, including the role of the promoter region, RNA polymerase, nucleoside triphosphates terminator.

7.3.4 State that eukaryotic RNA needs the removal of introns to form mature mRNA.

THURSDAY, 9/2• The information needed to make

polypeptides is carried in the mRNA from the nucleus to the ribosomes of eukaryotic cells. This information is decoded during translation. The diagram below represents the process of translation.

• State the name of the next amino acid which will attach to the polypeptide. (1)

• Explain how the amino acid was attached to the tRNA. (3)

• Alanine / Ala 1

• an activating enzyme attaches amino acid to the tRNA;

• specific enzyme for specific tRNA;• recognizes tRNA by its shape / chemical properties;• energy (ATP) is needed;• amino acid attached at end;• amino acid attached at CCA; 3 max

Happy Thursday! 9/2/2010

Explain the process of translation.• (Total 9 marks)

• consists of initiation, elongation and termination;• mRNA translated in a 5' to 3' direction;• binding of ribosome to mRNA;• small sub-unit then large;• first / initiator tRNA binds to start codon / to small subunit of ribosome;• AUG is the start codon;• second tRNA binds to ribosome;• large subunit moves down mRNA after a second tRNA binds;• amino acid / polypeptide on first tRNA is transferred / bonded to amino acid on second tRNA;• peptide bonds between amino acids / peptidyl transferase;

requires GTP;• movement of ribosome / small subunit of ribosome down the mRNA;• loss of tRNA and new tRNA binds;• reach a stop codon / termination;• polypeptide released;• tRNA activating enzymes link correct amino acid to each tRNA;• (activated) tRNA has an anticodon and the corresponding amino acid attached;• [9]

7.4 Translation

7.4.1 Explain that each tRNA molecule is recognized by a tRNA-activating enzyme that binds a specific amino acid to the tRNA, using ATP for energy.

7.4.2 Outline the structure of ribosomes, including protein and RNA composition, large and small subunits, three tRNA binding sites, mRNA binding sites.

7.4.3 State that translation consists of initiation, elongation, translocation, termination.

7.4.3 State that translation consists of initiation, elongation, translocation, termination.

7.4.3 State that translation consists of initiation, elongation, translocation, termination.

7.4.3 State that translation consists of initiation, elongation, translocation, termination.

7.4.4 State that translation occurs in a 5  3 direction.

7.4.5 Draw and label the structure of a peptide bond between two amino acids.

7.4.6 Explain the process of translation, including ribosomes, polysomes, start codons and stop codons.

7.4.7 State that free ribosomes synthesize proteins for use primarily within the cell, and that bound ribosomes synthesize proteins primarily for secretion or for lysosomes.