Transcript Cellular Basis of Inheritance

Cellular Basis of Inheritance
Chapter 9
Cells come from other
cells
• Repair
• Growth
• Reproduction
– Asexual Reproduction
– Sexual Reproduction
Sexual Reproduction
• Genetic Material comes from 2 parents
Asexual Reproduction
• Genetic Material comes from 1 parent
– Budding
– Cloning
– Fragmentation
– Sporulation
Binary Fission (Prokaryotes
way of Asexual Reproduction)
• Cell division in prokaryotes produce 2
identical daughter cells
The Cell Cycle
• Sequence of growth
and division of a cell
• Interphase = period
of growth
• Mitosis = period of
nuclear division
• Cytokinesis = period
of cell division
Cell Cycle Movie
Limits on Cell Size
• Diffusion – becomes slow and
inefficient as the cell becomes larger
• Surface Area/Volume Ratio – as a cell
increases, its volume increases faster
than its surface area
• DNA content – if a cell doesn’t have
enough DNA to program its
metabolism, it cannot survive
Chromosome Structure
• Chromatin Uncondensed form
• Genetic material
spends most of its
time as chromatin
• During prophase,
the chromatin
material coils up and
condenses to
become a
chromosome (coiled
form of DNA)
Chromosome Structure
• Chromosomes condensed rod
shaped structures
made of coiled DNA,
(only seen in mitosis
phase)
Chromosome Structure
The DNA wraps around a histone core to form
bead like structures known as nucleosomes
• This occurs during prophase
• Histones – proteins that help DNA coil
Chromosome Structure
• The nucleosomes
coil even more
• The coils become
the chromosome
• From smallest to most coiled is the
following
– Double helix
– DNA and histone protein
– Coil
– Super coil
– Chromosomes
Centromere
• Each half of a
replicated chromosome
is called a chromatid
• Sister chromatids:
The 2 identical halves
of the double structure
are sister chromatid;
exact copies of each
other
• Centromere: site
where sister chromatids
are adjoined
Chromosome or
chromatid?
Replication
• 1 chromosome
• 1 chromatid
• 1 chromosome (doubled)
• 2 chromatids (sisterchromatids)
Mitosis and Meiosis
How and Why Cells Divide
Onion root
Interphase
• G1 phase= Growth
phase
• S phase = synthesis
phase – make copy
of DNA
• G2 phase – Growth
and cell
maintenance for
preparation of
division occurs:
- for example copying
organelles
Interphase
• Gene replication
occurs
• Cell maintenance
occurs:
–
–
–
–
make ATP
excrete wastes
make proteins
produce new
organelles
Prophase
• Chromatin coils up
into visible
chromosomes
Prophase
• Centrioles begin to
migrate to opposite
sides of the cell
• Nucleus begins to
dissappear as
nuclear envelope
and nucleolus
disintegrate
Prophase
• Spindle
fibers –
form
between
centrioles
- And attach to
chromosom
es
Metaphase
• Chromosomes line
up at the center of
the cell
(along the equator)
• (shortest phase)
Anaphase
• Chromatids split and
one is pulled to each
of the poles;
centromere first
• Each chromatid is
identical
• One copy of each
chromosome goes
to each side (pole)
Telophase
• Final phase of mitosis
• Chromatids reach opposite
ends of the cell
• Opposite events of
prophase:
– chromosomes unwind into
chromatin
– spindle breaks down
– nuclear envelope forms
around 2 new sets of
chromosomes (to create 2
new nuclei)
– nucleolus forms in each
nucleus
• Cytokinesis begins (before
telophase is finished)
End of Mitosis
• Nuclei go back into interphase
• Cytokinesis begins
Cytokinesis
• Animal Cells:
– Form Cleavage
Furrow
– membrane pinches off
and half of the cell
contents go to each
new daughter cell
• Plant Cells:
– forms Cell Plate
– because plants have
a rigid cell wall, the
plasma membrane
does not pinch in; a
cell plate forms across
the equator
When do cells divide?
•
Growth of a multicellular organism - due to increase in # of cells, not
size of cells!
– Living things grow by producing more cells, not cells getting bigger same
size now as baby, size or organism depends on number of cells
– Cell division enables multicellular organisims to grow and develop from a
single fertilized egg – one single cell can divide to form a multicellular
human
– Cells can grow a little bit ex fat cells don’t divide once reach puberty –but
can grow much larger
•
•
•
•
- even if not growing in size still produce new cells to replace old
Cell division even when fully grown to renew and repair cells or
replace old that die of wear and tear or accidents ex bone marrow
supplys new blood cells
*Red blood cells only live 120 days 2.5 million new must be
made/second?, but must be controlled growth (or cancer)
* Cells that line the digestive system organs – go through entire
cell cycle in 6 hours