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