Download How cells duplicate

How cells
duplicate
Stem cells
• Stem cells are undifferentiated cells
• 2 main types: embryonic and adult
• Adult stem cells are multipotent, meaning
they have a limited potential for
differentiation
• Embryonic stem cells are pluripotent,
meaning they can differentiate into any cell
type.
Binary Fission
• A form of asexual reproduction (no
gametes) used in eukaryotes (us)
• Involves 2 processes: Mitosis and
Cytokinesis
• These processes run in tandem (together)
Important terms
• Homologous: roughly the same
• Sister chromatids: a doubled chromosome
• Centromere: center point that holds 2 sister
chromatid together.
• Centrosomes: cytoskeletal structures that form
the centers of the soon to be divided cells
• Microtubules: small protein structures that
connect to parts of the cell and help pull them to
their appropriate sides during cell division.
Interphase
• Most of the cell’s life is spent in this phase.
• Interphase contains 3 phases:
• G1 phase: the first stage in a newborn cell
(gap or growth phase)
• S phase: DNA duplication takes place.
• G2 phase: the 3rd stage in a cell (gap or
growth phase), it happens before division
• G phases serve as checkpoints.
Mitosis: Step 1, Prophase
• 2 steps
• Step 1: the chromatin condense into
compacted chromosomes
• Step 2: the nuclear envelope breaks down
and microtubules connect the
kinetochores to the centrosomes.
Mitosis: Step 2, Metaphase
• The microtubules line up the
chromosomes at the cells equator
Mitosis: Step 3, Anaphase
• The chromatids separate and the new
chromosomes move towards the poles.
Mitosis: Step 4, Telophase
• The separating chromosomes reach the
poles. The nuclear envelopes re-form and
the chromatin DEcondenses.
• Cytokinesis is taking place durring this
step.
Cytokinesis
• How cells divide
• First the cells doubles all its organelles
(except nucleus, we just witnessed why).
• Next it forms a protein ring around its
center at the plasma membrane. This ring
begins contracting during telophase and
completes shortly after.
Sexual Reproduction
• We have to form the gametes.
• We break the 46 chromosomes into 2
pairs of 23 in 2 different cells.
• Haploid: a cell that only contains one set
of chromosomes (ex. Gamete)
• Diploid: a cell that contains both sets of
chromosomes (ex. Fertilized egg a.k.a.
zygote)
Meiosis I : Separating
chromosomes
• How we create sex cells
• Metaphase I: generate chromosome pairs
and line them up in the center of the cell
• Anaphase I: homologous chromosomes
separate
• Telophase I & cytokinesis: first cell
division resulting in 2 haploid cells.
Meiosis II: Cutting chromosomes
• Remember: we are working with 2 cells
now (we split in meiosis I)
• Metaphase II: line up each chromosome
in the center of the cell
• Anaphase II: pull apart the chromosomes.
• Telophase II and cytokinesis: divide into
2 cells each. Results in 4 haploid cells.