1. Chapter 5 (Please do read every single page)
DNA & Chromosomes
Chapter 5
(Please do read every single page)

2. Learn…
Nucleotides
Nucleosides
DNA
RNA

4. Facts The DNA in each human cell is enormous
End to end - all 24 chromosomes would stretch 1.8 metres
Cell diameter is = WHO CARES!!!
Nucleus diameter is = few um
How is it squeezed in and also controlled?

5. DNA Deoxyribonucleic acid It is a Macromolecule
Made of Subunits - nucleotides
IT HAS DIRECTIONALITY
dictated by the free end groups
always written 5’ to 3’ direction for each single strand

6. Three-dimensional structure
Figure 9.7

7. NUCLEIC ACID STRUCTURE
DNA and RNA can be VERY VERY VERY large macromolecules with several levels of complexity
1. Nucleotides form the repeating units
2. Nucleotides are linked to form a single strand
3. Two strands can interact to form a double strand - for DNA this is called the double helix
4. The double helix is nursed and managed by P’s
which bend and twist the DNA - eventually resulting in 3-D structures in the form of chromosomes

8. Nucleotides
The nucleotide is the repeating structural unit of DNA and RNA
HOW IS IT CONSTRUCTED?
Many varieties
Each has three components
A phosphate group
A pentose sugar
A nitrogenous base

9. Figure 9.8

10. The red atoms below are found within individual nucleotides
However, they are removed when nucleotides join together to make strands of DNA or RNA
A, G, C or T
A, G, C or U
Figure 9.9
The structure of nucleotides found in (a) DNA and (b) RNA

11. Base + sugar  nucleoside
Example
Adenine + ribose = Adenosine
Adenine + deoxyribose = Deoxyadenosine
Base + sugar + phosphate(s)  nucleotide
Adenosine monophosphate (AMP)
Adenosine diphosphate (ADP)
Adenosine triphosphate (ATP)
Next…

12. SIMPLE PLAN OF A SINGLE STRANDED NUCLEOTIDE CHAIN

13. Just LOOK here to determine if this is RNA or DNA
LEARN WHICH ATOMS CONNECTS THE SUBUNITS TO EACH OTHER…
Figure 9.11

14. Other important nucleotides within cells
ATP
ADP
AMP
Base always attached here
Phosphates are attached there
Figure 9.10

15. 5’ to 3’ how?
Individual nucleotides are covalently linked together by phosphodiester bonds
A phosphate connects the 5’ carbon of one nucleotide to the 3’ carbon of another
Therefore the strand has directionality
5’ to 3’
The phosphates and sugar molecules form the backbone of the nucleic acid strand
The bases project from the backbone

16. DNA Deoxyribonucleic acid Macromolecule Subunits - nucleotides
5’ to 3’ direction for each single strand
Two strands run in opposite directions

18. Minor groove
Major groove
The two strands are not equally spaced because of bond angles
P’s and the those enzymes that manage DNA interact with the DNA mainly via the major groove.

19. Definitions -
Genome - The complete set of INFORMATION in an organism’s DNA
That is the haploid complement for all organisms
Chromosome - A single molecule of DNA
Circular or linear
Gene - a section of the DNA coding for the production of a single protein*
Karyotype - figure or picture showing the full set of chromosomes from a cell during cell division when they are condensed and visible...
*simplification of the current data

20. Human Karyotype

21. Human DNA facts
Genome = 3.2 billion base pairs of DNA across 24 different distinct chromosomes (22 automomes + X + Y)
Take about 9.5 years to read out loud (without stopping) the three billion pairs of bases in one person's genome sequence
Biologist simply say 23 pairs of chromosomes
For diploid cells = 6.4 billion base pairs per somatic cell
Each ? is a single enormous DNA double-helix - chromosome

22. Genome sizes
Humans do not have the most chromosomes - Plants tend to have these
Humans do not have the largest gemone size - Fish tend to have these
An ant species has just 1 chromosome
No real association between genome size and evolutionary complexity - human near the middle some where

24. Chromosomes Structure
During the cell cycle the structure of chromosomes changes visibly
Interphase state = very fine threads
Metaphase state = distinct defined chromosomes
Ends of chromosomes are known as telomeres
Middles, where the spindles attach, as centromeres

25. Nucleolus Within the nucleus are one or more nucleoli.
The nucleolus is the coming together of genes from different chromosomes that are involved in making ribosomes.
An average, healthy cell can produce up to ribosomes per minute.

26. Nucleolus

27. DNA management
10,000 fold difference in size between DNA helix stretched out and the size of a metaphase chromosome - How?
Answer = Proteins associated with DNA
Histone Proteins (H1, H2a, H2b, H3, and H4)
DNA plus these proteins is called Chromatin

29. Nucleosome Complex consisting of 200 bp of DNA
8 histone proteins in core
H1 histone stabilizing
Core = 146 bp DNA and two each of H2a, H2b, H3 and H4

30. Diameter of the nucleosome
Vary in length between 20 to 100 bp, depending on species and cell type
Figure 10.14
Diameter of the nucleosome
Overall structure of connected nucleosomes resembles “beads on a string”
This structure shortens the DNA length about seven-fold
10-45
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31. Play a role in the organization and compaction of the chromosome
Figure 10.14
10-47
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32. Higher Order Folding DNA -double-stranded helix is 2 nm thick
Nucleosome - 11 nm thick
30nm chromatin fibre - 30 nm thick
Chromatin loops nm thick
Condensed chromatin nm thick
Chromosome (mitotic) nm thick
DNA is wrapped or looped using a protein matrix

33. Figure 10.21
10-63

34. 10-64 Figure 10.21 Compaction level in euchromatin
During interphase most chromosomal regions are euchromatic
Compaction level in heterochromatin
Figure 10.21
10-64

35. Heterochromatin
Regions close to telomere and centromere are classes as heterochromatin based on observations
These are not very active for transcription
DNA thought to be tightly packed here
Few proteins can enter region - it it too tight for them to get to the DNA

36. Chromatin Remodeling Complexes
Large Protein complexes which selectively act at the nucleosome level to unwind DNA to allow proteins access
IMPORTANT control mechanism in the cell.
Transcription occurs when needed.