Chromosomes

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Homework

Cell Cycle Review

• What are the three big parts of the cell cycle, in order?

• What happens in each one?

Interphase• Put this diagram in your notebooks (you

don’t need the cell pictures or texts)

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Most of the cell’slife is spent in interphase.

Interphase then has some sub-phases, like how “adulthood” is broken down into “young adult,” “mature adult,” “middle-age,” etc.

Interphase

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G1 (Gap 1) - Cell growth

Interphase

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G1 (Gap 1) - Cell growth

S (Synthesis) - Copy DNA to prepare for later reproduction

Interphase

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G1 (Gap 1) - Cell growth

S (Synthesis) - Copy DNA to prepare for later reproduction

G2 (Gap 2) - Lots of protein synthesis, and ensuring “good health”

Interphase

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G1 (Gap 1) - Cell growth

S (Synthesis) - Copy DNA to prepare for later reproduction

G2 (Gap 2) - Lots of protein synthesis, and ensuring “good health”

G0 (Gap zero) - Resting

Interphase

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How is interphase analogous to a human life cycle?

Cell Cycle

• The cell reproduction that we are talking about at the moment is called:

• Asexual reproduction. Just by looking at the term, what do you think it probably means?

Cell Cycle

• The cell reproduction that we are talking about at the moment is called:

• Asexual reproduction: Reproduction that does not involve two cells fusing together.• Mitosis is asexual reproduction. Why?

Cell Cycle• Asexual reproduction: Reproduction that does not

involve fertilization (two cells combining their DNA). Produces offspring genetically identical to the parent.• Mitosis• Other examples include:

• Binary fission• Budding• Fragmentation• Parthenogenesis• Spore formation

Cell Cycle

• Sexual reproduction: Reproduction in which two cells contribute their chromosomes to create a new cell with a unique genome.• Example: Fertilization of sperm and egg

Chromosomes

• Chromosome: A very long, supercoiled strand of DNA.• Different organisms have

different numbers of chromosomes in every cell.

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Chromosomes• Gene = Region of a

chromosome that codes for one protein.

Chromosomes

• Different chromosomes carry different genes.• For instance, in humans,

everyone has a gene called INSR at the same place on chromosome #19. INSR is a gene that codes for a receptor protein that detects insulin.

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Chromosomes

• Everyone has two chromosome #19s in each of your cells, so you have two INSR genes.

• And two chromosome #1s, two #2s, etc.• Demo

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Chromosomes

• Homologous chromosomes: Two versions of the same chromosome. They code for all the same proteins, but they may each make those proteins with slightly different sequences and shapes.

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Chromosomes• Because we have homolgous

chromosomes, meaning two copies of every chromosome, our cells are called diploid.• Latin/Greek Word Roots: Di

• Diploid: A cell with 2 copies of each chromosome.

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Chromosomes

• Diploid:

• Haploid: A cell with only 1 copy of each chromosome.• Sperm and eggs only.

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Chromosomes

• So, a normal diploid human cell has 46 chromosomes: 23 kinds of chromosome, 2 versions of each.

• After a human cell undergoes mitosis, how many chromosomes do you think each of the two offspring cells will have?

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Chromosomes

• Each cell will have 46! They are identical copies of the parent cell, after all.

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Chromosomes

• To get from one diploid cell with that many chromosomes to two offspring also with that many chromosomes, DNA replication will happen during interphase.

• Find three people, and explain to them how DNA replication works.

Chromosomes• DNA Replication

• A strand of DNA “unwinds” and “unzips”• Extra DNA nucleotides are attached to their base

pair partners• This creates two DNA molecules that are entirely

identical to each other

• Keep this in mind for the future.