Biology 3.3

Describe the role of DNA in relation to gene expression

Cell Types

• What is the difference between prokaryotes and eukaryotes?

• Devise a table that highlights the differences in general structure of plant, animal and bacterial cells at the organelle, DNA and chromosome levels. Find the info on page 43 and 44 of the course book.

Cell organelles

• What are the roles of the following organelles?• Match up the cell structure and function cards.

Karyotypes

• Chromosomes arranged in groups according to size, shape and banding pattern.

• Prepared from nuclei of cultured white blood cells ‘frozen’ at metaphase stage of mitosis.

Spot the abnormality

Chromosomes

• Explain chromosomes using the following words: (Pg 50 + 59)– DNA– Chromatin– Histone– Centromere– Chromatid

Homework

• Read 42 – 44, highlight, and add to glossary

Proteins

• Proteins are polymers of amino acids

• A.k.a polypeptides

Functions of Proteins

• Enzymes

• Structure

• Carry oxygen

• Fight disease

• Cell membrane

• Chemical messengers

Amino Acids

• Central C atom with 4 groups attached:– Carboxyl group (COOH)– Amine group (NH2)– H atom– Variable ‘R’ group

‘R’ group

• Can be – Hydrophilic– Hydrophobic– Acidic (containing another COOH group)– Neutral– Basic (containing another NH2 group)– Sulfur containing (Cysteine and methionine)

Peptide Bond

• Holds Amino Acids together

• Between COOH of one amino acid and NH2 of next

• Condensation reaction – H2O produced

Protein Structure

• Complex 3-D shape

• Denaturation – irreversible, due to extreme heat or pH

• Globular eg enzymes

or

• Fibrous eg keratin

• 4 levels to structure

Primary Structure

• Amino Acid sequence determined by genetic code

Secondary Structure

• Folding of polypeptide chain due to H-bonding

• Alpha-helix – a spiral or coil with ‘R’ groups projecting

• Beta pleated sheet – flat arrangement

Tertiary Structure

• Secondary structure folded and held by disulfide bridges, hydrophobic or hydrophilic attractions, and weak H-bonds.

Quaternary Structure

• One or more polypeptide chains, and in some cases non-protein components, aggregated together.

Protein Structure Animation

• Lets put the 4 structures together!

• Watch this animation

• Now build a protein – (strip of paper)– Sequence along the chain– Fold – helix/pleated sheet– Hydrophilic and hydrophobic folding– More than one polypeptide chain together

Homework

• Read pg 45 + 46, highlight/draw, and add to glossary

Enzymes

• Lower activation energy without being used up in a reaction.

• Substrate specific animation

• Named by adding –ase to substrate

• Co-enzymes complete active site

• Anabolic – joining molecules (p/s)

• Catabolic – breaking down molecules (dig/resp)

Lowering activation energy

Enzyme action

• Lock and key model animation

• Induced fit

• Inhibitors compete for active site

Enzymes and membranes

• Metabolic pathways involve succession of reactions.

• Enzymes grouped together and bound to membrane

• Eg. Mitochondria, chloroplasts, golgi bodies

Factors affecting enzymes

• pH

• Temperature

• Substrate and enzyme concentration

• Co-enzymes and heavy metals

Homework

• Read pg 47 + 48, highlight and add to glossary

• Work sheet – fill word gaps “Proteins and enzymes”

DNA

• Define the following terms:– Nucleotide (give full name of components)– Complementary bases (full names)– Double helix structure– Nucleic Acid– DNA– RNA

Purines and Pyrimidines

• Purines• Double ring• A + G

• Pyrimidines• Single ring• T, U +C

Anti-parallel nature

• 3’ and 5’ ends • The two nucleotide

strands run in opposite directions. Top strand 5’ to 3’ an bottom strand 3’ to 5’.

Introns and Exons

• Introns – a segment of DNA strand not coding for an amino acid sequence; – it is excised during the RNA processing stage

of protein synthesis.

• Exons – a segment of DNA coding for an amino acid.

Discovery

The discovery of introns led to the Nobel Prize in Physiology or Medicine in 1993 for Phillip Allen Sharp and Richard J. Roberts. The term intron was introduced by American biochemist Walter Gilbert:[7]

• "The notion of the cistron [...] must be replaced by that of a transcription unit containing regions which will be lost from the mature messenger - which I suggest we call introns (for intragenic regions) - alternating with regions which will be expressed - exons." (Gilbert 1978)

Functions of DNA and RNA

DNA• Passing on genetic

information • The chemical that

genes are made out of

RNA• Protein synthesis• Exists as tRNA or

mRNA

DNA replication

• Unwinding the molecule

• Breaking the bonds between the strands

• Replication (base pair matching)

• Repackaging

• Semi-conservative construction

• Animations + Biozone page

Okazaki fragments

• Short pieces of newly replicated DNA along the lagging strand that are later rejoined by DNA ligase.

• replication animation

Key Enzymes

• RNA and DNA polymerases

• DNA ligase

• DNA helicase

Write a statement to summarise the function of each enzyme using text pg 52 and photocopy of biozone page

Cell division