1. Transcription & Translation
IB Biology
Topic Topic
Structure of
DNA and RNA
DNA Replication
Transcription & Translation

2. Nucleotides 3 major nucleic acids: DNA & RNA DNA, RNA, ATP
Made of nucleotides (monomer)
Nucleotides:
One phosphate
One 5 carbon monosaccharide
One nitrogenous base

3. Bases: Adenine Guanine Cytosine Thymine Purines and Pyrimidines:
Uracil in place of thymine in RNA
Purines and Pyrimidines:

4. Monomers  Polymers Backbone: Alternating pentose-phosphate
Bases extend outward
Order of bases determine genetic code for organism
Covalent bonding between components

5. Single or Double Strand
RNA- always SS
A-U, G-C
DNA always DS
Bases are paired: complementary base-pairing
A-T, G-C
Hydrogen bonds
between bases

6. Anti-Parallel Arrangement
Deoxyribose + phosphate= phosphodiester bond (linkage)
Forms between hydroxyl group of 3’ carbon of deoxyribose and phosphate group to 5’ carbon of deoxyribose
New always added to 3’ carbon end
Result: Double strand has 2 directions

7. DNA Packaging Paired with histone proteins for organization
Nucleosome-
2 molecules of each of 4 different histones (8 histones total)
DNA- (-) charge and histones (+) charge
Between nucleosomes, often a 5th histone attached to linking string of DNA
Additional histone supercoiling

8. DNA Packaging, cont.
Supercoiling of DNA makes it inaccessible to transcription enzymes
Form of regulation
Only certain areas of DNA involved in protein synthesis

9. Types of DNA Sequences Highly Repetitive sequences: 5-300 base pairs
100,000 replicates of a certain type per genome
Clustered in discreet areas- satellite DNA
Dispersed throughout-
Coding function not known

10. Types of DNA Sequences, cont.
Protein Coding Genes
Provide base sequences proteins via ribosomes
Base sequences carried from the nucleus to the ribosomes via mRNA
Genes not fixed sequence of bases, but coding info (exons) mixed with non-coding fragments (introns)

11. Types of DNA Sequences, cont.
Structural DNA:
Highly coiled- has no coding function
Around centromere and near ends of chromosomes
Pseudogenes: lost coding function due to mutation involved with a base change

12. Types of DNA Sequences, Cont.
Short tandem repeats and DNA Profiling:
Most of our DNA is identical to every other human
Specific regions that show variation: polymorphisms
Polymorphisms are used for DNA profiling
Look at 13 specific loci: short tandem repeats (STRs) of 2-5 base pairs

13. Semi- Conservative Replication
Watson and Crick
Structure of DNA
Single strand of DNA used as template
Meselson and Stahl
Confirmed findings
Bacterial DNA replication process developed as result
Bacterial DNA:
Circular
No histone proteins
Single point of origin for replication of DNA
Eukaryotic DNA:
Linear
Has histones
Has thousands of points of origin

14. Semi-Conservative Replication, cont.
Replication steps:
1. Begins at origin, appears as a “bubble”
2. Helicase unzips H bonds between bases.
3. End of bubble replication fork
4. Bubbles enlarge in both directions and eventually fuse to produce 2 identical daughter strands

15. DNA Replication Elongation of DNA strand
1. Primer produced by primase at replication fork
Primer is 5-10 nucleotides of RNA
Primase allows joining RNA nucleotides that match DNA sequence
2. DNA polymerase III allows the addition of nucleotides in a 5’ to 3’ direction
3. DNA polymerase I removes primer from 5’ end and replaces it with DNA nucleotides
4. Topoisomerase (DNA gyrase)
stabilizes DNA above helicase

16. DNA Replication, cont. Anti-Parallel strands One 5’ 3’, one 3’ 5’
DNA only assembled in 5’  3’ direction due to DNA pol III.
3’ 5’ template strand made quickly and continuously- leading strand
5’ and 3’ template strand made discontinuously and in pieces- lagging strand
Pieces are called Okazaki fragments
Fragments are joined by DNA ligase

17. DNA Replication, cont. 1. Leading strand assembled continuously
2. Lagging strand assembled in Okazaki fragments
3. Primer, primase, and DNA pol III required to begin formation of each Okazaki fragment
4. Primer and primase needed only once for leading strand
5. DNA ligase attaches sugar-phosphate backbone together

18. Replication Proteins
Replication in prokaryotes and eukaryotes is almost identical

19. Speed and Accuracy of Replication
4000 nucleotides per second
Bacteria-
Speed essential, divide every 20 minutes
Remarkably accurate-
Few errors occur
Cells have repair enzymes that detect errors
Repair enzymes also used when cells are damaged by chemicals or high energy waves

20. Replication, DNA Sequencing, Human Genome Project
HGP required actual representation of nucleotide sequence in humans.
Sequencing DNA-
1970s Sanger developed sequencing procedure
Fragments of DNA copied through PCR (polymerase chain reaction)
Read and outline section on page
bring questions to class.