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Biology 102
Gene expression (cont.)/
Begin Cellular reproduction
Chapter 1
Lecture outline

Gene expression and regulation (cont.)
Mutations
 Regulation of gene expression


Cellular reproduction
Types of cellular reproduction
 Mitosis vs. meiosis
 Overview of mitosis/cell cycle
 Steps of mitosis

Chapter 1
Mutations

Mutations and protein synthesis

Source of mutations
 Exposure
to mutagens
 Errors in replication and transcription

Results of mutation: Changes in DNA can
result in changes in the proteins for which
they code
Chapter 1
Examples of Mutations
Chapter 1
Effects of mutations

Some are insignificant
More than one codon for most amino acids
 Third nucleotide position is often not important

 G-U-n
= valine
 U-C-n = serine
 C-G-n = arginine

Some are Harmful

Frameshift, missense or nonsense
Chapter 1
Effects of mutations

Mutations can be beneficial!
Altered proteins may be more effective than
originals
 Mutations are the source of genetic variation
 Significance to ability to evolve

X-men!
Chapter 1
Gene expression
Individual cells express only a small
fraction of their genes
 Gene expression is influenced by
developmental stage and environment


How is gene expression regulated?
Chapter 1
Regulation of gene expression (cont.)

Types of regulation

Frequency of transcription


Rate/amount of mRNA
translated



Turned on or off at promotor
region
Some mRNA stable, others
break down
Activation/inactivation of
proteins
Lifespan of the protein
Chapter 1
Types of cell reproduction

BinaryFission

(bacteria)
DNA replicated
Chapter 1
Membrane added
False-Color EM of Dividing Bacterium
Nuclear
material
Division plane
Cell wall
Cytoplasm
Chapter 1
Asexual reproduction by mitosis
New individuals
Chapter 1
Asexual Reproduction by Mitosis
Chapter 1
Functions of Mitosis in animals
Organs
Fertilized egg
(zygote)
Multicell stage
Mitotic
cell
division
Mitotic
cell
division &
differentiation
Tissues
Chapter 1
Mitosis, Meiosis, and the Sexual Cycle
Chapter 1
Focus on Mitosis
G0 :
nondividing
G1: Growth
S: Synthesis
of DNA;
chromosomes
duplicated
interphase
G2: Growth
Chapter 1
Interphase

DNA exists as
chromatin: The
chromosomes (blue)
are in the thin,
extended state




Wrapped around protein
DNA is 2 meters long!
Replicated while in this
form
The microtubules (red)
extend outward from
the nucleus to all parts
of the cell.
Chapter 1
Prophase

DNA condenses into
distinct chromosomes




Additional winding
Relationship of genes and
chromosomes
Diploid: Homologous pairs of
chromosomes
Sister chromatids held
together by centromere at this
stage


Mitotic spindle forms from
microtubules


Don’t confuse diploid with
sister chromatids!
Chromosomes attached
Nuclear membrane
disappears
Chapter 1
Metaphase

Chromosomes are
lined up in midline



The chromosomes have
moved along the spindle
microtubules
Homologous
chromosomes
aligned “head to toe”
At end of metaphase,
centromeres release
sister chromatids
Chapter 1
Anaphase


Sister chromatids have
separated, and one set
of chromosomes moves
along the spindle
microtubule to each
pole of the cell.
Cell still diploid, but
chromosomes now are
only single chromatids

Cell is always diploid
throughout this process!
Chapter 1
Telophase




The chromosomes have
gathered into two
clusters, one at the site
of each future nucleus.
Chromosomes begin to
decondense back to
chromatin
Nuclear membrane
forms
Followed by cytokinesis


Cytoskeleton “pinches” cell
into two parts
Plants form new cell wall
Chapter 1
Cytokinesis of a Ciliated Cell
Daughter Cells
Cleavage Furrow
Chapter 1
Cytokinesis in Plants
Vesicles fuse to
form cell wall
and membranes
Complete
separation of
daughter cells
Chapter 1
Mitosis: Review
Duplicated
chromosomes
remain elongated
Chromosomes
condense and
shorten
Late
Interphase
Early
Prophase
Centrioles have
also been
duplicated
Nucleolus
disappears;
Nuclear envelope
breaks down
Late
Prophase
Centrioles begin
to move apart;
Chapter 1
Spindle forms
Microtubules
attach to
kinetochores
Metaphase
Kinetochores
align at cell’s
equator
Mitosis: Review (cont.)
Free spindle
fibers push
poles apart
Anaphase
Chromatids
become
independent
chromosomes
One set of
chromosomes;
Begin unwinding
Telophase
Cytoplasm
divided along
equator
Cytokinesis
Each daughter
Nuclear
gets 1 nucleus &
envelope rehalf of
forms Chapter 1
cytoplasm
Next
Interphase
Spindle
disappears;
Nucleolus
reappears
How do cells “know” when to
stop dividing?

Cell senescence



Cells are programmed to stop dividing.
Cells of older people programmed to stop dividing
earlier (50x for newborn cells, 30x for aged person's
cells)
Growth control

Cell division inhibited by contact with other "like" cells.


Ex: wound closure.
Cancer cells do not exhibit growth control. Something has
gone haywire. They keep growing.
Chapter 1