Cell Cycle, Division, Diversity & Organisation · 2019-05-12 · Cell Cycle, Division, Diversity &...
Transcript of Cell Cycle, Division, Diversity & Organisation · 2019-05-12 · Cell Cycle, Division, Diversity &...
Cell Cycle, Division, Diversity
& Organisation• State that mitosis occupies only a small percentage of the cell
cycle.
• Describe, with the aid of diagrams and photographs, the main stages of mitosis (behaviour of the chromosomes, nuclear envelope, cell membrane and centrioles).
• Explain the meaning of the term homologous pair of chromosomes.
• Explain the significance of mitosis for growth, repair and asexual reproduction in plants and animals.
• Outline, with aid of diagrams and photographs, the process of cell division by budding in yeast.
• State that cells produced as a result of meiosis are not genetically identical (details of meiosis are not required).
• Define the term stem cell.
The Cell Cycle
• The events that take place as one parent
cell divides to produce two daughter cells
which then grow to full size.
– The daughter cells are genetically identical to
each other and to the original parent cell.
– In some cases the daughter cells are new
organisms
ChromosomesChromosome
arrangement
Stages of
the Cell
Cycle
Mitosis
• Nuclear division where 2 genetically identical nuclei are formed from one parent nucleus.
• Divided into 4 named phases:
– Prophase
– Metaphase
– Anaphase
– Telophase
Interphase
• The cell grows to full size.
• DNA replicates ready for the next round of cell division.
• The cell carries out its normal biochemical functions.
• Chromatin is not coiled & chromosomes are not visible.
Prophase
• The replicated chromosomes become supercoiled (short & thick).
• Now visible with a light microscope.
• Centriole divides and two daughters move to opposite poles.
• Spindle fibres form.
• Nuclear envelope disappears.
Metaphase
• The chromosomes line up
along the equator of the
cell.
• Each becomes attached to
a spindle thread by it’s
centromere.
Anaphase
• The centromere splits &
chromatids are pulled
apart.
• Spindle fibres shorten &
pull the chromatids towards
the poles.
Telophase
• A new nuclear envelope
forms around the
separated chromatids (now
called chromosomes).
• Spindle fibres break down.
• Chromosomes uncoil.
• Cytokinesis occurs
Timescales
• Cell cycle times vary from one species to the next.
– Some bacteria complete a whole cycle in 20 -30 minutes (given ideal conditions).
– Yeasts can take up to 4 hours.
– The fastest mammalian cell cycle is 9 – 10 hours for some intestine epithelial cells.
– Some mammalian cells can have a cycle time of over 200 hours.
– Fully differentiated cells rarely divide.
Stage G0
• G0 is the name given to the phase where a cell leaves
the cell cycle (either permanently or temporarily).
• Reasons for this:
– Differentiation
• Specialised cells no longer divide. They just do the
job they have specialised to do.
– DNA Damage
• Damaged cells do not divide.
– Aging
• Most cells only divide a certain number of times
then become senescent. Aging is the increase in
number of senescent cells.
Controlling the Cell Cycle
• Cells need to ensure they only divide
when they are ready to.
– When they have grown large enough.
– When replicated DNA is error free.
– When chromosomes are in their correct
position during mitosis.
• There are 3 checkpoints within the cell
cycle which check these process have
taken place correctly:
Checkpoints:
• Mitosis cannot proceed
unless this checkpoint is
passed
Plants v Animals v Yeasts
• Only certain plant cells (meristem cells) can divide.
• Plant cells do not have centrioles.– Spindle fibres are made in the cytoplasm.
• Plant cytokinesis starts with the formation of a cell plate across the equator of the cell.– A new cell membrane & cell wall is laid down along
this cell plate.
• Yeast cytokinesis by producing a small bud which pinches off from the cell.
Animals
Plants
Yeasts
Cleavage
Furrow
Buds
Cell plate
How long is each phase?
Why do we need mitosis?
• All organisms need to produce genetically identical cells for:– Growth
• Multicellular organisms grow by producing extra cells. Each cell must be able to carry out the same functions as existing ones.
– Repair• Damaged cells need to be replaced by new ones that are
able to perform the same functions.
– Asexual reproduction• Single celled organisms divide to produce two identical
organisms. Some multicellular organisms produce genetically identical offspring by mitosis.
– Replacement• RBCs & skin cells are constantly replaced.
Clones
• Genetically identical cells or entire
organisms.
– Bacteria produce clones by binary fission.
– Plants can produce clones by Vegetative
Propagation.
– Identical twins are clones.
– Artificial clones can be produced:
• Cuttings from plants.
• Mammalian clones (eg Dolly the Sheep)
Meiosis
• Details required for AS.Interphase, prophase 1, metaphase 1, anaphase 1, telophase 1, prophase 2, metaphase 2, anaphase 2, telophase 2, Homologous Chromosomes.
• Production of haploid daughter cells:
– Contain half the number of chromosomes as parent cell.
– Are genetically different from each other and from the parent cell.
– Used to make gametes for fusion into a zygote.
Specialised Cells
• Single celled organisms have a large
enough SA:Vol ratio to supply it with
enough oxygen & nutrients.
• Multicellular organisms have a lower
SA:Vol ratio.
– Not all cells are in contact with the outside
medium.
– They need specialised cells to perform
various functions.
Differentiation
• Where cells become specialised to
perform specific functions.
• Differentiation can involve changes to:
– Numbers of various organelles
– Shape of the cell
– Cell contents
– All three
Some Specialised Cells
• What are the functions of these cells:
– Erythrocytes
– Neutrophils
– Sperm cells
– Palisade cells
– Root Hair cells
– Guard cells
• Summarise the form and function of each.
Sperm Cells
Root Hair Cells
Tissues
• Multicellular organisms have several levels
of organisation:
– Specialised cells
– Tissues
– Organs
– Organ Systems
– Organisms
Animal Tissue Types
• There are 4 main categories of tissues:
– Nervous tissue
• Supports the transmission of electrical signals.
– Epithelial tissue
• Covers internal and external body surfaces.
– Muscle tissue
• Contracts to produce movement.
– Connective tissue
• Holds other tissues together or transports substances
between them.
• Summarise the form & function of each type.
Epithelial Tissue
• Different types:
– Squamous(small flat cells)
– Cuboidal(Cube-shaped cells)
– Columnar (Tall, thin cells)
Squamous Epithelium
• Flattened cells, thin layer.
• Ideal for lining blood vessels or forming the walls of alveoli.
– Provides very small distance for diffusion of oxygen & CO2.
• Cells held in place by a basement membrane of collagen – secreted by the epithelial cells.
Ciliated Columnar Epithelium
• Found on inner surface of
tubes (trachea, bronchi,
bronchioles, uterus,
oviducts).
• Often associated with
goblet cells.
• Cilia beat with synchrony &
rhythm to move the mucus.
Plant Tissue Types
• Plants consist of different tissue too:– Xylem tissue
• Transports water & minerals throughout the plant.
– Phloem tissue
• Transports organic nutrients throughout the plant
– Epidermal tissue
• Covers the surfaces of plants.
• Summarise the form & function of each type.
Organs
• A collection of tissues which are adapted
to perform a specific function for the
organism.
• Eg.
– Heart
– Leaf
Leaves as Photosynthetic Organs
• Photosynthesis requires:
– Light
– Water
– Carbon Dioxide
• Photosynthetic organs need to:
– Supply the requirements
– Carry out the reaction
– Remove the products
Organ Systems
• A number of organs working together to
perform a major function of the body.
• Eg:
– Digestive System,
– Cardiovascular System,
– Gas Exchange system.
Stem Cells
• Capable of becoming any one of the different cell types found in an organism.– They have a high potency
– Described as totipotent, pluripotent or multipotent
• Occur in small numbers in a body.• Bone marrow contains the multipotent stem cells for blood &
bone tissue.
• May be able to be used to repair damaged tissues without rejection problems.
Sources of Animal Stem Cells
• Embryonic Stem Cells.
– Totipotent at the 1-16 cell stage.
– Pluripotent after the blastocyst stage.
Sources of Animal Stem Cells
• Tissue (adult) Stem Cells.
– Multipotent.
– Although called Adult SC, are present from
birth.
– Found in specific areas (Eg bone marrow,
umbilical cord).
• Meristem
tissue.
– Pluripotent.
– Occur at tips
of roots &
shoots, and
in stems
(yellow areas
in diagram).
Sources of Plant
Stem Cells
Plant
Meristem• Xylem &
phloem
tissue
developing
from the
meristem
Xylem
Phloem
Uses of Stem Cells
• Research how some diseases might be treated using
stem cells:
– Heart disease/Type 1 diabetes
– Parkinson’s/Alzheimer’s diseases
– Repair of birth defects/injuries/burns
• Research also how stem cells might be used to develop
new drug treatments or further our biological knowledge.
• Summarise this work along with some of the ethical
considerations that have to be made when working with
stem cells.