Biology Lecture 10/28/14

Front 1

What are the key roles of cell division?

Back 1

Overview: The Key Roles of Cell Division
• The ability of organisms to produce more of
their own kind best distinguishes living things
from nonliving matter
• The continuity of life is based on the
reproduction of cells, or cell division

Front 2

What do multicellular organisms depend on cell division for?

Back 2

In unicellular organisms, division of one cell
reproduces the entire organism
• Multicellular organisms depend on cell division
for
– Development from a fertilized cell
– Growth
– Repair
• Cell division is an integral part of the cell cycle,
the life of a cell from formation to its own
division

Front 3

What kinds of questions are asked about division into daughter cells?

Back 3

What are the key components of the task required of the cell when it divides into two “daughter” cells?
1. What must happen?
2. What must be avoided?
3. What complicates or simplifies the process?
4. Must the cell remain intact (i.e. with a functioning
plasma membrane) throughout the entire process?

Front 4

What does cell division result in? And what is the exception?

Back 4

Most cell division results in daughter cells with
identical genetic information, DNA
• The exception is meiosis, a special type of
division that can produce sperm and egg cells
(meiosis is the subject of Chapter 13, in the next
unit)

Front 5

What is a genome?

Back 5

All the DNA in a cell = genome
• A genome can consist of a single DNA molecule
(common in prokaryotic cells) or a number of
DNA molecules (common in eukaryotic cells)
• DNA molecules in a cell are packaged into
chromosomes

Front 6

What are unique features of chromosomes in eukaryotes?

Back 6

Eukaryotic chromosomes consist of chromatin,
a complex of DNA and protein that condenses
during cell division
• Every eukaryotic species has a characteristic
number of chromosomes in each cell nucleus
• Somatic cells (nonreproductive cells) have two sets of chromosomes
• Gametes (reproductive cells: sperm and eggs)
have half as many chromosomes as somatic
cells

Front 7

How many chromosomes does each individual possess?

Back 7

Humans have 46 chromosomes
• We get 23 chromosomes from each of our
parents

Front 8

What is the distribution of chromosomes during eukaryotic cell division?

Back 8

Distribution of Chromosomes During
Eukaryotic Cell Division
• In preparation for cell division, DNA is replicated
and the chromosomes condense
• Each duplicated chromosome has two sister
chromatids (joined copies of the original
chromosome), which separate during cell
division
• The centromere is the narrow “waist” of the
duplicated chromosome, where the two
chromatids are most closely attached

Front 9

What do sister chromatids do during cell division?

Back 9

During cell division, the two sister chromatids of
each duplicated chromosome separate and
move into two nuclei
• Once separate, the chromatids are called
chromosomes

Front 10

The entire DNA content of a cell is?
a. Sister chromatids
b. Chromosomes
c. Genome
d. Centrosomes

Back 10

c. Genome

This is a pretty good answer, especially if
we’re talking about a prokaryote. But for a
eukaryote these really are just the nuclear
genome. There is also non-nuclear genetic
material in mitochondria and chloroplasts,
and this is technically part of the genome
as a whole.

Front 11

What makes up the x-shaped, DNA thing?

a. Sister chromatids
b. Centromere
c. Genome
d. Centrosomes

Back 11

a. sister chromatids

By this stage in the cell cycle the
replication of each chromosome has
already taken place. Each sister
chromatid is a copy of the chromosome
DNA material.

Front 12

What's the attachment point for the sister chromatids?

a. Sister chromatids
b. Centromere
c. Genome
d. Centrosomes

Back 12

b. Centromere

Front 13

How do sister chromatids separate?

Back 13

Chromosome duplication (including DNA replication) and condensation. Then, separation of sister chromatids into two chromosomes.

Front 14

What does eukaryotic cell division consist of?

Back 14

Eukaryotic cell division consists of
– Mitosis, the division of the genetic material in the nucleus
– Cytokinesis, the division of the cytoplasm
• Gametes are produced by a variation of cell
division called meiosis
• Meiosis yields nonidentical daughter cells that have only one set of chromosomes, half as many as the parent cell

Front 15

What does the cell cycle consist of?

Back 15

The mitotic phase alternates with interphase in the cell cycle
• The cell cycle consists of
– Mitotic (M) phase (mitosis and cytokinesis)
– Interphase (cell growth and copying of
chromosomes in preparation for cell division)

Front 16

What are the subphases of interphase?

Back 16

Interphase (about 90% of the cell cycle) can be
divided into subphases
– G1 phase (“first gap”)
– S phase (“synthesis”)
– G2 phase (“second gap”)
• The cell grows during all three phases, but
chromosomes are duplicated only during the S
phase

Front 17

What are the phases of Mitosis?

Back 17

Mitosis is conventionally divided into five
phases
– Prophase
– Prometaphase
– Metaphase
– Anaphase
– Telophase
• Cytokinesis overlaps the latter stages of mitosis

Front 18

What is G2 of Interphase characterized by?

Back 18

Nuclear envelope is still present, as are nucleoli
• Two centrosomes have formed
• Chromosomes have duplicated during S phase, but are still uncondensed here

Front 19

What is Prophase characterized by?

Back 19

Chromatin condenses
• Nucleoli disappear
• Mitotic spindle formation
• Lengthening microtubules move the centrosomes apart

Front 20

What is Prometaphase characterized by?

Back 20

Nuclear envelope breaks down
• Chromosomes very condensed
• Kientochores now present and some microtubules attach to them

Front 21

What is Metaphase characterized by?

Back 21

Centrosomes at opposite ends of the dividing cell
• Chromosomes line up at the “metaphase plate” equidistant between poles.
• Kinetochores are attached to microtubules

Front 22

What is Anaphase characterized by?

Back 22

Cohesin proteins cleaved
• Chromatids come apart
• Kinetochore microtubules shorten
• The cell elongates as non-kinetochore microtubules lengthen

Front 23

What are Telophase and Cytokinesis characterized by?

Back 23

Daughter cell nuclei form, with nuclear envelopes
• Nucleoli reappear
• Chromosomes decondense
• Spindles depolymerize

Front 24

What is the mitotic spindle?

Back 24

The mitotic spindle is a structure made of
microtubules that controls chromosome
movement during mitosis
• In animal cells, assembly of spindle
microtubules begins in the centrosome, the
microtubule organizing center
• The centrosome replicates during interphase,
forming two centrosomes that migrate to
opposite ends of the cell during prophase and
prometaphase

Front 25

What is an aster?

Back 25

• An aster (a radial array of short microtubules)
extends from each centrosome
• The spindle includes the centrosomes, the
spindle microtubules, and the asters

Front 26

What occurs during prometaphase and metaphase?

Back 26

During prometaphase, some spindle microtubules attach to the kinetochores of chromosomes and begin to move the chromosomes
• Kinetochores are protein complexes associated with centromeres
• At metaphase, the chromosomes are all lined up at the metaphase plate, an imaginary structure at the midway point between the spindle’s two poles

Front 27

What happens in Anaphase?

Back 27

• In anaphase, sister chromatids separate and
move along the kinetochore microtubules toward opposite ends of the cell
• Anaphase usually takes just minutes

Front 28

What occurs in telophase and cytokinesis?

Back 28

• Nonkinetochore microtubules from opposite
poles overlap and push against each other,
elongating the cell
• In telophase, nuclei form at opposite ends of
the cell
• Cytokinesis begins during anaphase or
telophase and the spindle eventually
disassembles

Front 29

The overlapping nonkinetochore microtubules function to:
a. Push the two poles or ends of a dividing cell apart.
b. Provide efficient electron transport.
c. Regulate glycolysis.
d. Both b. and c.

Back 29

a. Push the two poles or ends of a dividing cell apart.

Front 30

The two copies of a replicated eukaryotic chromosome are called:
a. Centrosomes.
b. Kinetochores.
c. Sister chromatids.
d. Cis and trans golgi.

Back 30

c. Sister chromatids

Front 31

On a eukaryotic chromosome the narrow “waist” region between chromosome arms is called the:
a. Centrosome.
b. Sister chromatid.
c. Genome.
d. Centromere.

Back 31

a. Centromere

Front 32

What stage of mitosis features an early mitotic spindle and condensation of chromatin within the nucleus?
a. S phase.
b. Telophase.
c. Prophase.
d. Metaphase.

Back 32

C. Prophase

Front 33

T or F. Mitosis only works on cells that are haploid, this is, carrying a single genome copy.

Back 33

False. Mitosis copies the chromosomes present in the cell and carefully divides the two copies of each chromosome to the two daughter nuclei. This works fine for a haploid cell OR for a diploid or other ploidy.