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The nucleus
Nuclear membrane
double membrane
Nuclear pores
Nucleolus
RNA production
Chromosomes
genetic material
Chromosomes and Cell Division
Chromosomes
What are they ?
How they are replicated?
Cell Division
Why are there two types: mitosis and meiosis?
How are they different?
How does meiosis produce new combinations
of genes?
What is a chromosome?
It is a linear strand of DNA in combination with
nuclear proteins
We refer to this complex of DNA and
proteins as chromatin
It is a linear array of genes
As a set - they are our genome
Chromosomes exist in different states
As visible structures seen during cell division.
Most of the time they are not visible because they exist
as uncoiled threads of chromatin distributed through out
the nucleus.
Chromosome basics.
The number of chromosomes present within the
nucleus is a characteristic of the species.
Chromosomes of humans and most other
eukaryotic species occurs in pairs.
Members of a chromosome pair are known as
homologues.
The state in which there are two copies of each
chromosome present is known as diploid.
Haploid – only one copy of a chromosome is
present
All of the somatic cells in our bodies are
diploid cells
The only cells in our bodies that are haploid
are our gametes – eggs and sperm
Human somatic cells have 46 chromosomes
diploid number (2n) = 46
23 from mom - 23 from dad
22 pairs are autosomes –true homologous pairs
1 pair is not necessarily homologous
- sex chromosomes
females are XX
males are XY – a non homologous
pair.
Figure 2.9
Figure 2.8
Cell division
mitosis is the process of cell division in which
one cell becomes two identical daughter cells
development
renewal
regeneration
The cell cycle
• S phase: DNA synthesis
• G phase: gap for growth
• M phase: mitosis (nuclear
division)
• Cell division or cytokinesis
is part of G1
Replication of chromosomes
• Replication is the
process of duplicating a
chromosome
• Occurs prior to division
• Replicated copies are
called sister chromatids
• Held together at centromere
Figure 2.12
Mitosis
Purpose: to make copies of cells and their DNA
• Replicated chromosomes align at the metaphase plate.
• Sister chromatids separate and move to opposite poles.
• Nuclear membranes form around each new nucleus.
• Division of cytoplasm or cytokinesis occurs.
Prophase
• Replicated
chromosomes
condense.
• Microtubules organize
into a spindle
Metaphase
• Chromosomes line up
on the metaphase
plate.
• Spindle microtubules
are attached to
centromeres of
chromosomes.
Anaphase
• Centromeres of sister
chromatids separate
• Chromosomes move
to opposite ends of the
cell
Telophase
• Nuclear membranes
form
• Spindle disappears
• Division of cytoplasm
occurs (cytokinesis)
Cytokinesis
Cytoplasmic division
occurs after nuclear
division is complete.
Two cells are formed.
Figure 2.15
Cell cycle control
Proteins called checkpoint proteins monitor
progression through the cell cycle.
Cell division
mitosis is the process of cell division in which
one cell becomes two identical daughter cells
Cell death
apoptosis is the process of cell death in which
cells signal their own demise in a programmed way
development
response to abnormality
Apoptosis
Programmed cell death is part of normal development
chicken
embryo
Death receptor binds signal molecule.
Capase enzymes destroy proteins.
Cells fragment.
Phagocytes engulf cell remanants.
Different amounts of apoptosis create
feet with digits versus webbing.