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

Learn… Nucleotides Nucleosides DNA RNA

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?

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

Three-dimensional structure Figure 9.7

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

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

Figure 9.8

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

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…

SIMPLE PLAN OF A SINGLE STRANDED NUCLEOTIDE CHAIN

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

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

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

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

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.

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

Human Karyotype

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

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

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

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 10 000 ribosomes per minute.

Nucleolus

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

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

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 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display

Play a role in the organization and compaction of the chromosome Figure 10.14 10-47 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display

Higher Order Folding DNA -double-stranded helix is 2 nm thick Nucleosome - 11 nm thick 30nm chromatin fibre - 30 nm thick Chromatin loops - 300 nm thick Condensed chromatin - 700 nm thick Chromosome (mitotic) - 1400 nm thick DNA is wrapped or looped using a protein matrix

Figure 10.21 10-63

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

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

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.