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Ms. Doshi

Chapters 6.1 to 6.5

Cell Division

6.1 Telomere DiseaseThis child has a disease. • The name of the disease is

Hutchinson-Giford progeria Syndrome.

What are some symptoms of this disease?• Children grow old very quickly and die

by age 13. What is the cause of this disease?• The child is born with shorter than

normal telomeres.

What are telomeres?• Telomeres are non-coding, repetitive

DNA, located at the end of every chromosome. They also protect the chromosome.

6.1 Telomeres in Cell Division• Every time a cell divides,

telomeres become shorter.• After a critical number of

cell divisions, the telomeres are too short.

• The critical number is different for different species. For humans, the critical number is 50 cell division.

• Telomeres that are too short causes loss of functional, essential DNA and cell death.

6.2 Chromosome Structure (Prokaryotes)

single, circular chromosome• attached to one site of

the cell membrane

6.2 Chromosome Structure(Eukaryotes)

Free floating linear chromosomes• They are located in the

nucleus• They are wrapped around

proteins. The name of these proteins are histones.

What do histones do?• They keep the DNA from

getting tangled• They keep the DNA tightly and

efficiently packed in an orderly manner inside the cell.

Some prokaryotes have histones.

6.3 Prokaryotes: Binary Fission

What happens in Binary Fission?1. Replication: an exact

copy of the cell’s DNA is made

2. Each copy of the cell’s DNA attaches to different sites in the parent cell.

3. The parent cell divides.4. Each copy of the DNA is

now in a new daughter cell.

Parent Cell

Daughter Cell

6.4 Eukaryotic Cells: Cell Division in Somatic Cells

There are 2 main phases to cell division in the somatic cells of eukaryotic cells:Interphase: 1. Gap 1 (G1): long2. DNA Synthesis (S)3. Gap 2 (G2): shortMitotic Phase (M Phase)4. Mitosis5. CytokinesisSomatic Cells: Cells that form the body of the organism. These are NOT sex cells (gametes).

Questions1. What are the symptoms of Hutchinson-Giford progeria Syndrome?2. What is the cause of Hutchinson-Giford progeria Syndrome?3. What are telomeres?4. What is the critical number of cell divisions in humans? Why is this

number important?5. What is the chromosome structure in prokaryotes? 6. What is the chromosome structure in eukaryotes?7. What do histones do?8. True or False: Histones are found in eukaryotes and some prokaryotes. 9. How do prokaryotic cells divide? (Name of the process)10. How do eukaryotic cells divide? (Name of the process) 11. What are the parts of cell division in somatic cells of eukaryotic cells?12. What are somatic cells?

6.4 Eukaryotic Cells: Cell Division in Somatic Cells

Interphase: • The cell grows and

prepares to divide. Mitotic phase: • nucleus and

chromosomes divide• rest of cell structures

divide• shortest period of cell

division

6.4 Interphase: Gap 1 (G1)

• The cell’s primary growth phase.

• Normal cellular functions occur in this phase.

• Make proteins, remove waste, etc.

• LONG• Example: Neurons & Heart

Muscle Cells spend a long time in the G1 phase.

6.4 Interphase: DNA Synthesis (S) • Replication occurs at this

phase. • Every chromosome makes

an exact copy of itself. • Before replication: – The chromosome is a long,

linear piece of genetic material.

• After replication: – The chromosome is a pair

of identical, long, linear pieces, joined together by a centromere.

DNA Synthesis: Chromosome Structure

Before DNA Replication After DNA Replication

6.5 DNA Synthesis: DNA Replication

• Why can DNA replicate? • Key feature of DNA:

complementaritythe base on one strand of DNA always has the

same pairing partner (complementary base)A-T, G-C

6.5 DNA Synthesis: DNA ReplicationDNA replication happens in 2 steps:

• Unwinding The coiled double stranded DNA

unwinds and separates into 2 strands.

• Rebuilding Enzymes connect a nucleotide with

the appropriate base to the growing new strand.

A binds with T, G binds with C.

RESULT: Two double stranded DNA, identical to the cell’s original double-stranded DNA.

6.4 Interphase: Gap 2 (G2)

• Second period of growth.• Cells prepare for cell

division. • Shorter than G1.

6.4 Mitotic Phase: Mitosis (M)

• The parent cell, with its duplicated chromosomes, divides.

6.4 Mitotic Phase: Cytokinesis (M)

• The cytoplasm from the parent cell is divided into 2 daughter cells.

• Each daughter cell has a set of the parent cell’s DNA and other cell structures.

Questions

1. What happens in Interphase?2. What happens in the Mitotic phase?3. What is shorter: The M phase or Interphase?4. What is longer: G1 or G25. What happens in the S phase?6. What are the 2 steps of DNA Replication?7. What happens in the G1 phase?8. What happens in the G2 phase?9. What happens in Mitosis?10. What happens in Cytokinesis?