Biology 1001- Section 8: The Molecular Basis of Inheritance

DNA

The substance of inheritance (genes). Directs development of biochemical, anatomical, physiological and even behavioural traits.

Genes

On chromosomes. A basic physical and functional unit of heredity made of DNA that is passed from parents to offspring

Chromosomes

Contains DNA and proteins. It is a thread-like structure in the nucleus of a cell made of DNA tightly coiled around proteins.

Smooth Strain

Pathogenic(disease causing)

Has a protective capsule that shields the bacteria from the host’s immune system.

Rough Strain

Non-pathogenic

Lacks the protective capsule

Transformation

A process in which a cell takes up external DNA from its environment, causing a change in its genotype (genetic makeup) and phenotype (observable traits).

Bacteriophage/Phage

Virus that infects bacteria

T2 Phage

• Made of DNA enclosed in a protein coat.

• Infects Escherichia coli (E. coli), a common intestinal bacterium.

• Uses the host cell’s enzymes and building blocks to reproduce.

• Once infected, E. coli cells release many new T2 phages.

• The T2 phage essentially reprograms E. coli to make more copies of itself.

Molecular Diversity

Different proportions of nitrogenous bases

J. Watson and F. Crick

Determined the three dimensional structure of DNA

Double helix

DNA is a double-stranded helical

Anti parallel

Subunits run in opposite directions

Complementary

Each contains the information to reconstruct the other

Semi conservative Model

Each new DNA molecule has one original (parental) strand and one newly made strand.

Conservative Model

One new daughter molecule keeps both original strands, while the other has two entirely new strands.

Dispersive Model

Both new DNA molecules contain mixed segments of old and newly synthesized DNA.

M. Meselson and F. Stahl

Devised experiments to distinguish among the three models of DNA template strands

Bacterial Chromsome

A single circular piece of DNA that holds all the essential genetic information for a bacterium and is tightly packed into the cell’s nucleoid region.

Chromatin

The complex of DNA and proteins (mainly histones) that forms chromosomes within the nucleus of eukaryotic cells

Histones

Small basic(positively-charged) proteins

• ~100 amino acids, rich in lysine and arginine

• Five types: H1, H2A, H2B, H3A, H3B

Nucleosome

The basic unit of DNA packaging in eukaryotic cells. It is a structure made of DNA wrapped around histone proteins that helps package DNA and regulate gene activity.

30 nm Fibre

A thicker, more tightly folded version of chromatin created when 10 nm nucleosome fibres coil and fold together, helped by interactions between histone tails, linker DNA, and H1.

• Common during interphase, though its exact structure is still debated.

Looped DomainS

Looped domains are large chromatin loops attached to a protein scaffold, which further condense to form tightly packed metaphase chromosome

Metaphase Chromsomes

During metaphase, the looped domains coil and fold even further to form the highly condensed 700 nm chromosomes. This structure keeps the specific order of genes intact.

Heterochromatin

Tightly packed, inactive chromatin that is generally inaccessible for gene expression.

Euchromatin

Loosely packed, active chromatin that is accessible for gene expression.