chapter 11 the continuity of life: cellular reproductionlemastm/teaching/bi102/chapter 11... ·...

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Chapter 11

The Continuity of Life: Cellular Reproduction

Chapter 11: Cellular Reproduction

What is Cellular Reproduction?

Answer: The division of a parent cell into two daughter cells

Requirements of Each Daughter Cell:

1) Necessary genomic information (DNA)

2) A complete assortment of cytoplasmic materials

Cell Types Differ in Reproductive Process:

A) Prokaryotes = Binary Fission

Figure 11.31 – Audesirk2 & Byers

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A) Prokaryotes = Binary Fission (“splitting in two”)


• Prokaryote DNA:

• Single circular chromosome

• Attached to cell wall

Steps in Binary Fission:

1) Chromosome replicates

2) Cell elongates (membrane production)

• Chromosomes pulled apart

3) Membrane pinches in middle

4) Daughter cells formed

Can be rapid process (~ 20 minutes)



B) Eukaryotes


1) Mitosis: Daughter cells genetically identical to parental cell

• Functions: A) Growth (we all start as a single cell…)

B) Maintenance (skin flakes off…)

C) Repair (wounds heal…)

D) Asexual reproduction (produces clone of parent…)

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B) Eukaryotes



Cell Cycle:

The cell activity from one cell

division to the next

Interphase (majority of time):

• Synthesize material for

cell division

1) G1 Phase (Growth phase 1)

2) S Phase (Synthesis phase)

3) G2 Phase (Growth phase 2)

• Replicate DNA

• Acquire materials

• Grows

During G1 phase, cell is sensitive

to signals:S Phase

• Metabolically active

• No division

Cancer = Signal

Failure

G0 Phase



B) Eukaryotes



Cell Cycle:



Mitotic Cell Division:

• Division of cytoplasm

1) Mitosis

2) Cytokinesis

• Division of DNA

One copy of DNA and half of

cytoplasm distributed to two (2)

daughter cells

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Chromosomes contain:

1) Linear DNA strand

2) Histones (Packaging proteins)

Chromosome condensed only during cell

division; extended other times (chromatin)

• Identical copies; connected at centromere

When condensed, DNA has already replicated

Centromere


How is DNA in Eukaryotes Organized?

Answer: DNA is packaged into chromosomes

Sister

Chromatid

Sister

Chromatid

Separated at mitosis

DNA Organization:

• Chromosomes often occur in pairs called homologues (“to say the same thing”)

• Both members are same length and contain same genes in same order

Diploid: Cells with pairs of homologous

chromosomes (2n)

Haploid: Cells with only one of each type

of chromosome (n = haploid number)

• Found in sex cells (e.g., sperm / egg)

• Found in most cells of human body

Karyotype: Entire set of chromosomes from

a single cell

Eyegene Eyegene


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Human Karyotype:

Haploid Number:

n = 23

Diploid Number:

2n = 46(23 pairs)

Sex

Chromosomes:

X and Y

Female = XX

Male = XY

Organism

Human

Gorilla

Cat

Shrimp

Potato

Diploid # (2n)

46

48

38

254

48Figure 11.9 – Audesirk2 & Byers



B) Eukaryotes



Cell Cycle:





1) Mitosis

2) Cytokinesis

• Division of DNA



daughter cells

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• Chromosomes condense

• Spindle microtubules form

• Chromosomes captured by spindles (kinetochore)


Process of Mitosis:Phase 1: Prophase

Phase 2: Metaphase

Nuclear

envelope

breaks down

Centrioles:

Anchor microtubules

• Chromosomes line up along

cell equator

• Kineticore „tug-o-war‟


• Sister chromatids move to

opposite poles


Process of Mitosis:

Phase 3: Anaphase

Centrioles:

Anchor microtubules

• Kineticore motors

• Sister chromatids separate

Phase 4: Telophase

• Spindle microtubules disintegrate

• Nuclear envelops (re)form

• Chromatids relax (expand)


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B) Eukaryotes



Cell Cycle:





1) Mitosis

2) Cytokinesis

• Division of DNA



daughter cells

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• Microfiliments form ring around cell equator and

contract to pinch cytoplasm into two parts


Cytokinesis in Animal Cells:


• Stiff cell walls of plant cells do not allow for cells to divide by pinching

at the „waist‟


Cytokinesis in Plant Cells:


1) Carbohydrate-filled vesicles line up on cell equator

2) Cells fuse, producing cell plate

3) Fusion continues until new cell wall divides cell

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B) Eukaryotes

1) Mitosis

2) Meiosis: Daughter cells contain ½ the genetic information of parental

cells

• Sexual reproduction (produces gametes)


What is the Advantage to Sexual Reproduction?

Answer: Allows for reshuffling of genes to produce genetically unique

offspring better suited to environment...

Mutations in DNA are source of genetic variability:

• Allele: Alternate form of a given gene (e.g., eye color)

Eye

color

Most genes have two or more alleles

Blue

Allele

Brown

Allele

Green

Allele


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Reshuffling Genes (Alleles) to Benefit Organism - Example:

Motionless AlleleFreezes when

predator approaches

Bright AlleleColoration stands out

Motion AlleleMoves when

predator approaches

Camouflage AlleleColoration blends in

Motionless AlleleFreezes when

predator approaches

Camouflage AlleleColoration blends in

Sexual Reproduction

Dinner

Asexual

Reproduction

Dinner

Asexual

Reproduction




B) Eukaryotes

Figure 11.18 / 11.21 – Audesirk2 & Byers

1) Mitosis


cells

• Begin with: Parent diploid cell (2n = 46)

Similar to mitosis except cell goes through two nuclear divisions:

A) Meiosis I: Homologous chromosomes pair up separate (2n n)

Chiasma:

Region where paired

chromosomes joined

Paternal chromosome

Maternal chromosome

Prophase I Metaphase I Anaphase I Telophase I

Table 11.1• Finish with: Four daughter haploid cells (n = 23)

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B) Eukaryotes

1) Mitosis:


cells

B) Meiosis II: Sister chromatids separate (mitosis revisited…)

Prophase II Metaphase II Anaphase II Telophase II


How Meiosis Produces Genetic Variability:

1) Shuffling of homologous chromosomes creates new combinations of

chromosomes:

Potential

results of

meiosis I:

2n = 23 = 8

2n = 6

During metaphase I:


Humans = 223 = 8 million


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2) Crossing over creates chromosomes

with new combinations of genes

3) Fusion of Gametes adds further

variability:

Sperm = 8 million unique gametes

Egg = 8 million unique gametes

Fusion = 6 trillion possibilities


How Meiosis Produces Genetic Variability:


Example - Humans

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