Cell division - AQA Chromosomes and DNA Flashcards
(26 cards)
Chromosomes carry genetic information in a molecule called
DNA
A type of cell division ensures that when a cell divides each new cell produced has the same genetic information.
Mitosis
DNA
exists in a cell’s nucleus within structures called
Chromosomes
Each section of a chromosome that contains the code for the production of a particular protein
Gene
Each human body cell contains how many chromosomes
46 Chromosomes arranged into 23 pairs
In females, the two chromosomes are identical in shape.
XX
Males
XY
Mitosis
Cells divide when:
an organism grows
an organism becomes damaged and needs to produce new cells
A growing and dividing cell goes through a series of stages called the
cell cycle
.
The first stages of the cell cycle involve cell growth, then
synthesis
of
DNA
. The single strand of DNA that makes up each chromosome produces an exact copy of itself.
The cell undergoes a type of cell division called
mitosis
.
What happens in mitosis
The cell begins to divide.
The DNA replicates to form two copies of each chromosome.
The nuclear membrane breaks down. The chromosomes line up across the centre of the cell.
One set of chromosomes is pulled to each end of the cell, and the nucleus divides.
The cytoplasm and cell membranes divide to form two identical cells.
What happens during the cell cycle
Cell growth
DNA synthesis – the chromosomes are now double stranded
Further growth occurs, and the DNA is checked for errors
Mitosis
The cytoplasm separates – two cells are formed
Temporary cell resting period or the cell stops dividing
Stem cells
are cells that have not
undergoed
differentiation
. A cell which has not yet become
specialised
is called undifferentiated.
Adult stem cells can be found in several regions of the body, including the:
brain
eyes
blood
heart
liver
bone marrow
skin
muscle
How do adult stems cells work
Adult stem cells can differentiate into related cell types only, for example,
bone marrow
cells can differentiate into blood cells and cells of the
immune system
but not other cell types.
Risks and benefits of stem cells in medicine
Medical treatments with stem cells can help conditions such as diabetes and paralysis. An embryo can be produced with the same genes as the patient in a process called therapeutic cloning. These stem cells will not be rejected by the person receiving them, so they can be used for medical treatments. There are some risks using stem cells for medical treatments such as the transfer of viral infections. Some people also have ethical concerns or religious objections to their use.
Where does cell division occur in plants
Meristems
Specialised cells in animals
Circulatory system-Transport substances, defend the body, regulate temperature
Excretory system-Remove waste products and unwanted substances, regulate the water content of the body
Muscular system - Bring about movement
Nervous system- Respond to internal and external stimuli and conditions, carry messages for the body work as a coordinated whole
Respiratory system- Deliver oxygen for respiration and remove waste
Reproductive system- Bring about fertilisation to produce new offspring
Skeletal system- To bring about movement, support and protect internal structures, produce blood cells, store and release calcium
Specailised cells in plants
Leaf Palisade mesophyll Carry out photosynthesis
Spongy mesophyll Allow gases to circulate for the exchange of gases between the leaf and the environment, carry out some photosynthesis
Guard cells Open and close to control the exchange of gases – carbon dioxide, water vapour and oxygen
Phloem Sieve tubes Transport products of photosynthesis, including sugars and amino acids, from the leaf to where they are needed
Companion cells Provide the energy required for transporting substances in sieve tubes
Xylem Xylem vessels Transport water and dissolved minerals from the roots, up the plant
Growing points Meristem Produce new cells as they divide
Stem cells use
They could be used to replace cells that have been damaged or destroyed, eg:
in type 1
diabetes
in cases of
multiple sclerosis
, which can lead to
paralysis
in cases of
spinal cord
or
brain
injury, that have led to paralysis
The stem cells used could be:
embryonic stem cells
adult stem cells
What are embryonic stem cells
Embryonic stem cells can differentiate into a wider range of cell types, but are difficult to obtain and their use raises ethical challenges. The best source is the five-day-old embryo.
Adult stem cells?
Adult stem cells will differentiate into a narrower range of cell types. Bone marrow transplants are an example of adult stem cell transplant. Bone marrow cells will differentiate into different types of blood cell. Bone marrow transplants are carried out:
ther clkone
Benefits and risks associated with the use of stem cells in medicine
Clinical issues
There is no guarantee how successful these therapies will be, for example the use of stem cells in replacing nerve cells lost in Parkinson’s disease patients.
The current difficulty in finding suitable stem cell donors.
The difficulty in obtaining and storing a patient’s embryonic stem cells. These would have to be collected before birth - some clinics offer to store blood from the umbilical cord when a person is born.
Mutations have been observed in stem cells cultured for a number of generations, and some mutated stem cells have been observed to behave like cancer cells.
Cultured stem cells could be contaminated with viruses which would be transferred to a patient.
