GENETICSGENETICSRegents ReviewRegents Review

Wednesday, May 25Wednesday, May 25thth and Thursday, May and Thursday, May 26th26th

Ms. MendelsonMs. Mendelson

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Mr. MullerMr. Muller

DNA StructureDNA Structure

Double helix Double helix Watson and CrickWatson and Crick

Subunits (building blocks) : nucleotidesSubunits (building blocks) : nucleotides

Nucleotides are composed of a sugar, Nucleotides are composed of a sugar, phosphate and a nitrogenous base phosphate and a nitrogenous base Sugar and phosphate backboneSugar and phosphate backbone Bases: rungs of a ladderBases: rungs of a ladder

DNA MoleculeDNA Molecule

Organization of Genetic Organization of Genetic Information Within a Cell Information Within a Cell

NucleusNucleus

Chromosomes are structures which Chromosomes are structures which contain DNA.contain DNA.

DNA is composed DNA is composed

of genes.of genes.

KaryotypingKaryotyping

46 chromosomes in 46 chromosomes in

human body cellshuman body cells

(23 pairs)(23 pairs)

23 chromosomes in23 chromosomes in

human gametes human gametes

(sex cells)(sex cells)

Base PairingBase Pairing

Adenine (A) pairs with Thymine (T) Adenine (A) pairs with Thymine (T)

Cytosine (C) pairs with Guanine (G)Cytosine (C) pairs with Guanine (G)

( Complementary base pairs).( Complementary base pairs).

Held together by relatively weak hydrogen Held together by relatively weak hydrogen bondsbonds

DNA ReplicationDNA Replication

DNA molecule untwists and unzipsDNA molecule untwists and unzips

Enzymes match up free floating Enzymes match up free floating nucleotides to one of the original nucleotides to one of the original

DNA strandsDNA strands

One DNA strand acts as a template One DNA strand acts as a template (pattern or guide) for a new strand.(pattern or guide) for a new strand.

In order to ensure genetic continuity, DNA In order to ensure genetic continuity, DNA replication must occur before cell division.replication must occur before cell division.

TranscriptionTranscription

DNA is used as a template to make mRNADNA is used as a template to make mRNAOccurs in the nucleusOccurs in the nucleus4 bases of RNA: Adenine (A), Uracil (U), Guanine 4 bases of RNA: Adenine (A), Uracil (U), Guanine (G) and Cytosine (C)(G) and Cytosine (C) DNA RNADNA RNA

A UA U T AT A C GC G G CG C

mRNA leaves the nucleus and travels to the mRNA leaves the nucleus and travels to the ribosome of the cell.ribosome of the cell.

TranslationTranslation(Protein Synthesis)(Protein Synthesis)

At the ribosome, mRNA is used to At the ribosome, mRNA is used to synthesize a protein (polypeptide).synthesize a protein (polypeptide).Proteins are made up of a chain of amino Proteins are made up of a chain of amino acids.acids.Transfer RNA molecules (tRNA) bring the Transfer RNA molecules (tRNA) bring the amino acids to the ribosome.amino acids to the ribosome.The anticodon of the tRNA pairs up with The anticodon of the tRNA pairs up with the codon (3 bases) of mRNA.the codon (3 bases) of mRNA.

Let’s PracticeLet’s Practice

DNA- A-T-G-T-A-A-G-C-T-A-T-A-G-C-CDNA- A-T-G-T-A-A-G-C-T-A-T-A-G-C-C

mRNA- U-A-C-A-U-U-C-G-A-U-A-U-C-G-GmRNA- U-A-C-A-U-U-C-G-A-U-A-U-C-G-G

tRNA- A-U-G-U-A-A-G-C-U-A-U-A-G-C-CtRNA- A-U-G-U-A-A-G-C-U-A-U-A-G-C-C

Amino acidsAmino acids Tyr- Ile- Arg- Tyr- ArgTyr- Ile- Arg- Tyr- Arg

Gene ExpressionGene Expression

Each cell uses only some of the genetic Each cell uses only some of the genetic information it contains.information it contains.

Proteins are synthesized only from genes Proteins are synthesized only from genes that are expressed or “turned on;” all other that are expressed or “turned on;” all other genes are not expressed or “turned off.”genes are not expressed or “turned off.”

Ex: genes that code for liver enzymes are Ex: genes that code for liver enzymes are not expressed in nerve cellsnot expressed in nerve cells

Gene ExpressionGene ExpressionInfluenced by the environmentInfluenced by the environment

Example: Himalayan RabbitExample: Himalayan Rabbit

- cold temperature turns on gene for black - cold temperature turns on gene for black pigmentpigment

Example: identical twins raised separatelyExample: identical twins raised separately

- twin living in city may develop cancer - twin living in city may develop cancer

while twin living in the country may notwhile twin living in the country may not

MutationsMutations

A change/error in the linear sequence of a A change/error in the linear sequence of a DNA moleculeDNA molecule

A random alteration of DNAA random alteration of DNA

Source of variationSource of variation

Mutagens (agents that can cause damage Mutagens (agents that can cause damage to DNA): UV light, X-rays, pollutants, to DNA): UV light, X-rays, pollutants, tobacco smoke, asbestostobacco smoke, asbestos

MutationsMutations

If mutation occurs in the sex If mutation occurs in the sex

cells, it may be passed on to offspring.cells, it may be passed on to offspring.

If mutation occurs in the body cells, it may If mutation occurs in the body cells, it may only be passed on to other body cells; only only be passed on to other body cells; only affects the individual.affects the individual.

Types of Mutations: substitution, deletion, Types of Mutations: substitution, deletion, addition, inversion.addition, inversion.

Types of MutationsTypes of Mutations

(Different colors represent different genes)(Different colors represent different genes)

How do DNA mutations affect How do DNA mutations affect proteins?proteins?

Change in the nucleotide sequence of Change in the nucleotide sequence of DNA may lead to a change in the amino DNA may lead to a change in the amino acid sequence of a proteinacid sequence of a protein

The shape of the protein may be affected The shape of the protein may be affected (incorrect folding)and the protein doesn’t (incorrect folding)and the protein doesn’t do its job (malfunctions).do its job (malfunctions).

Example: Sickle Cell AnemiaExample: Sickle Cell Anemia

Genetic EngineeringGenetic Engineering

Transferring DNA from one organism to Transferring DNA from one organism to anotheranotherEx: transferring the human insulin gene Ex: transferring the human insulin gene into a plasmid (circular ring of bacterial into a plasmid (circular ring of bacterial DNA) and then inserting this plasmid into DNA) and then inserting this plasmid into a host cell (bacterial cell) a host cell (bacterial cell) As bacterial cell divides, so does human As bacterial cell divides, so does human insulin gene. Human insulin can be used insulin gene. Human insulin can be used to treat people with diabetes. to treat people with diabetes. Reduction in cost and side effects.Reduction in cost and side effects.

Using Bacteria PlasmidsUsing Bacteria Plasmids(Think of insulin production!)(Think of insulin production!)

What next???

You must now go home and study more on your own

Good luck to all of you on the upcoming regents exam

to be given

Wednesday June 22, 2005