Paper 1: Topic 1 Cell Biology - Cell division (LV) Flashcards
Name the genetic material found in all living cells
DNA
State where the genetic material is located in eukaryotic cells
Contained inside the nucleus
State where the genetic material is located in prokaryotic cells
Free in the cytoplasm
Exists as a nucleoid and some bacteria can also have additional small loops of DNA called plasmids
Describe how DNA is arranged in eukaryotic cells
As a linear chromosomes
Explain the term chromosome
A coiled length of DNA
State how many chromosomes are found in human somatic (body) cells
46
State how many chromosomes are found in human gametes
23
Explain the term diploid
A full set of chromosomes
This is represented as ‘2n’
Explain the term haploid
Half a set of chromosomes
This is represented as ‘n’
Explain the term ‘cell cycle’
A series of events in which a cell grows, replicates its DNA and then divides to form daughter cells
How do human somatic cells divide?
Mitosis
What is the function of mitosis?
To produce two GENETICALLY identical daughter cells
Why do multicellular organisms use mitosis?
To produce new cells:
a) For growth of tissues and organs
b) To repair damaged tissues and organs
* Remember do not just say “growth and repair” you must say ‘of tissues and organs’ as well*
Describe what happens to the chromosome number when a cell undergoes mitosis
It is maintained/kept constant
i.e. remains as 2n (diploid)
State the 3 main events during mitosis
DNA replication
Division of DNA
Splitting of the cell into 2
Explain what events occur inside a human somatic (body) cell BEFORE it takes part in mitosis
The cell increases in size
The sub-cellular structures (organelles) are replicated
The DNA is replicated (copied) so that there is double the quantity of DNA inside the cell
Describe the shape of a chromosome after it has replicated
It will appear as a cross
The 2 strands of DNA are held together by a centromere
Describe the relationship between the 2 arms of a chromosome after it has replicated
They are genetically identical
This means they carry the same genes and alleles
Describe the main events that take place during mitosis Hint: 6 key events
- The chromosomes line up in the middle of the cell along the equator
- Special protein fibres pull the chromosomes apart
- Half of each chromosome is pulled to the opposite pole of the cell
- Membranes form around the outside of each set of chromosomes (to form 2 nuclei inside the one cell)
- The cell splits equally into 2
Describe how prokaryotic cells divide
Binary fission
Explain the key events that occur during binary fission Hint: 4 events
- The circular DNA (nucleoid) and plasmids replicate
- The cell increases in size and the circular DNA moves to the poles of the cell
- The cytoplasm divides and new cell walls are formed
- 2 daughter cells are formed each has a circular DNA but they can have variable numbers of plasmids
Describe the main features of cell division in bacteria
Occurs by binary fission
Occurs very quickly (~once every 20 minutes)
How can you calculate the number of bacteria present after a given period of time?
Calculate the number of minutes in the time period
Divide the number of minutes by 20 (to calculate the number of divisions the bacteria will undertake).
Call this answer ‘x’
Calculate 2 to the power ‘x’ i.e. 2x
This will be the number of cells present after the specified time period.
Define the term stem cell
An unspecialised cell that can replicate to produce more unspecialised cells
All these cells can then differentiate to become specialised cells
Explain the term differentiation
The process of an unspecialised cell changing its shape, chemical content and organelle content to become a specialised cell
What controls differentiation?
The switching on and off of certain genes inside the unspecialised cell
State 2 sources of stem cell
Early embryos
Umbilical cord (after birth)
Adult bone marrow
What is special about early embryo stem cells?
They can differentiate into ANY type of specialised cell
How are adult stem cells different from embryo stem cells?
Embryo stem cells can differentiate into any type of specialised cell but adult stem cells can only differentiate into certain types of specialised cells e.g. red blood cells
How can stem cells be used in medical research
Either type of stem cell can be grown in science laboratories to produce clones
These clones can then be stimulated to differentiate into specific specialised cells
Explain what is meant by the term ‘specialised cell’
A cell that has changed its shape, chemical content and/or the organelle content of itself to become suited for a specific function
Describe what changes occur in stem cell when it differentiates into a red blood cell
Change in shape = it changes from spherical to biconcave
Change in chemical content = it produces a lot of haemoglobin
Change in organelle content = it breaks down its mitochondria and nucleus
State 3 examples of how stem cells can be use to cure disease
- Adult stem cells taken from the bone marrow of a healthy person can be used to replace faulty blood cells in a patient
- Embryonic stem cells can be used to replace faulty cells e.g. insulin producing cells can be used to treat people with diabetes nerve cells can be used to treat people with spinal cord injuries (paralysis)
- Stem cells can be used for therapeutic cloning – they are taken from the patient stimulated to differentiate into the required specialised cells and then returned to the same patient.
What is the advantage of using a patient’s own stem cells in therapeutic cloning?
The specialised cells formed from the patient’s stem cells are genetically identical to the patient’s cells and are therefore not rejected
What are carried on each chromosome?
Each chromosome carries a large number of genes.
What is a gene?
A section of DNA that codes for the production of one specific protein
Describe how chromosomes are normally found in somatic (body) cells
In body cells the chromosomes are normally found in pairs.
Where are stem cells found in plants?
In the meristematic tissue i.e. root tips and shoot tips
What is special about meristematic tissue in plants?
Meristem tissue in plants can differentiate into ANY type of plant cell, THROUGHOUT the life of the plant.
State two concerns people have with stem cell treatments
The use of stem cells has potential risks such as transfer of viral infection
Some people have ethical or religious objections.
State an advantage for horticulturists who using plant stem cells
Stem cells from meristems in plants can be used to produce clones of plants quickly and economically.
State 2 benefits of the use of plant stem cells in research and treatments
Rare species can be cloned to protect from extinction.
Crop plants with special features such as disease resistance can be cloned to produce large numbers of identical plants for farmers.
