How Cells Reproduce

1
How Cells Reproduce

• Biology 1030
• Principles of Biology

2
Understanding Cell Division

• What instructions are necessary for inheritance?
• How are those instructions duplicated for
  distribution into daughter cells?
• By what mechanisms are instructions parceled out
  to daughter cells?

3
Reproduction

• Parents produce a new generation of cells or
  multicelled individuals like themselves
• Parents must provide daughter cells with
  hereditary instructions, encoded in DNA, and
  enough metabolic machinery to start up their own
  operation

4
Division Mechanisms

• Eukaryotic organisms
• Mitosis
• Meiosis
• Prokaryotic organisms
• Prokaryotic fission

5
Roles of Mitosis

• Multicelled organisms
• Growth
• Cell replacement
• Some protistans, fungi, plants, animals
• Asexual reproduction

6
Meiosis

• Functions only in sexual reproduction
• Precedes the formation of gametes (sperm and
  eggs) or spores

7
Chromosome

• A DNA molecule attached proteins
• Duplicated in preparation for mitosis

8
Sister Chromatids

• Each chromosome and its copy stay attached to
  each other as sister chromatids until late in the
  nuclear division process
• Attach at the centromere

9
Nucleosome

• A nucleosome consists of part of a DNA molecule
  looped twice around a core of histone proteins

10
Organization of Chromosomes
DNA
one nucleosome
DNA and proteins arranged as cylindrical fiber
histone
11
Cell Cycle

• Cycle starts when a new cell forms
• During cycle, cell increases in mass and
  duplicates its chromosomes
• Cycle ends when the new cell divides

12
Interphase

• Usually longest part of the cycle
• Cell increases in mass
• Number of cytoplasmic components doubles
• DNA is duplicated

13
Stages of Interphase
14
Control of the Cycle

• Once S begins, the cycle automatically runs
  through G2 and mitosis
• The cycle has a built-in molecular brake in G1
• Cancer involves a loss of control over the cycle,
  malfunction of the brakes

15
Stopping the Cycle

• Some cells normally stop in interphase
• Neurons in human brain
• Arrested cells do not divide
• Adverse conditions can stop cycle
• Nutrient-deprived amoebas get stuck in interphase

16
Chromosome Number

• Sum total of chromosomes in a cell
• Somatic cells
• Chromosome number is diploid (2n)
• Two of each type of chromosome
• Gametes
• Chromosome number is haploid (n)
• One of each chromosome type

17
Human Chromosome Number

• Diploid chromosome number (n) 46
• Two sets of 23 chromosomes each
• One set from father
• One set from mother
• Mitosis produces cells with 46 chromosomes two
  of each type

18
(No Transcript)
19
Lots of DNA

• Stretched out, the DNA from one human somatic
  cell would be more than two meters long
• A single line of DNA from a salamander cell would
  extend for ten meters

20
Stages of Mitosis

• Prophase
• Metaphase
• Anaphase
• Telophase

21
Bipolar Mitotic Spindle

• Consists of two distinct sets of microtubules
• Each set extends from one of the cell poles
• Two sets overlap at spindle equator
• Moves chromosomes during mitosis

microtubule of bipolar spindle
22
Mitosis

• Period of nuclear division
• Usually followed by cytoplasmic division
• Four stages
• Prophase
• Metaphase
• Anaphase
• Telophase

23
Early Prophase - Mitosis Begins

• Duplicated chromosomes begin to condense

24
Late Prophase

• New microtubules are assembled
• One centriole pair is moved toward opposite pole
  of spindle
• Nuclear envelope starts to break up

25
Transition to Metaphase

• Spindle forms
• Spindle microtubules become attached to the two
  sister chromatids of each chromosome

26
Metaphase

• All chromosomes are lined up at the spindle
  equator
• Chromosomes are maximally condensed

27
Anaphase

• Sister chromatids of each chromosome are pulled
  apart
• Once separated, each chromatid is a chromosome

28
Telophase

• Chromosomes decondense
• Two nuclear membranes form, one around each set
  of unduplicated chromosomes

29
Results of Mitosis

• Two daughter nuclei
• Each with same chromosome number as parent cell
• Chromosomes in unduplicated form

30
Cytoplasmic Division

• Usually occurs between late anaphase and end of
  telophase
• Two mechanisms
• Cleavage (animals)
• Cell plate formation (plants)

31
Animal Cell Division
32
Cell Plate Formation
33
When Control Is Lost

• Growth and reproduction depend on controls over
  cell division
• Checkpoint proteins
• Growth factors invite transcription of genes that
  help the body grow
• Other proteins inhibit cell cycle changes, such
  as after chromosomal DNA gets damaged
• When all checkpoint mechanisms for a particular
  process fail, a cell loses control over its
  replication cycle
• An example of this is cancer

34
Squamous cell carcinoma on man's face and nose
Melanoma
35
Neoplasms

• Are abnormal masses of cells that lost controls
  over how they grow and divide
• Benign grow slowly and retain surface
  recognition proteins that keep them in a home
  tissue (noncancerous)
• Malignant grow and divide abnormally,
  disrupting surrounding tissues physically and
  metabolically (cancerous)

36
HeLa Cells

• Line of human cancer cells that can be grown in
  culture
• Descendents of tumor cells from a woman named
  Henrietta Lacks
• Lacks died at 31, but her cells continue to live
  and divide in labs around the world

37
Ms. Henrietta Lacks
38
Culturing Cells

• Growing cells in culture allows researchers to
  investigate processes and test treatments without
  danger to patients
• Most cells cannot be grown in culture