AQA Bio A Level Unit 2 Flashcards
How does the cell prepare for nuclear division after DNA replication? (3)
1 Replicating organelles;
2 Increasing/synthesising protein;
3 ATP synthesis;
In the cell cycle, in which phase does DNA replication occur?
Interphase
What term is used to describe the mass of uncondensed DNA in a nucleus during interphase?
Chromatin
What determines how long a cell spends in interphase as a proportion of its cell cycle? (2)
- How rapidly that type of cell divides;
- Rapidly dividing cells spend much less time in interphase;
Does DNA replication change the chromosome number? Explain your answer. (2)
- No
- Chromosomes are replicated to give two chromatids – but each pair of chromatids is still just one chromosome. (count the centromeres…)
What happens to the mass of DNA in DNA replication?
It doubles
In which phase of mitosis do chromosomes condense?
Prophase
In which phase of mitosis do chromosomes line up on the equator?
Metaphase
Which organelle produces the spindle fibres?
Centrioles
How many chromatids would there be in a human cell at metaphase of mitosis? Explain your answer (2)
- 92;
- Each of the 46 chromosomes consists of two sister chromatids
In which phase does the nuclear membrane break down?
Prophase
What do spindle fibres attach to in mitosis?
Centromeres
In which phase of mitosis do chromatids separate?
Anaphase
What is the consequence of uncontrolled cell division?
Formation of tumours – which may be cancerous.
Suggest likely targets of anti-cancer drugs.
- Prevention of DNA replication – e.g. modified nucleotides that cannot be joined together, or inhibition of DNA polymerase
- Prevention of cell division, often by inhibiting spindle-fibre formation.
Why do anti-cancer drugs cause side-effects?
- All tissues need cells that divide.
- Anti-cancer drugs often cannot discriminate and have their effects on both cancer cells and healthy cells.
Do bacteria divide by mitosis?
No. They do not have chromosomes.
How do bacteria divide?
By binary fission. They replicate their genetic material and then spilt in half.
As they do not have linear DNA and chromosomes, what forms does bacterial genetic material take? (2)
- Circular DNA
- Plasmids
How are plasmids distributed during bacterial fission?
Randomly. Plasmids are replicated, but the daughter cells each receive a variable number of them.
what are the 3 types of pathogens?
Bacteria
viruses
Fungi
what do viruses lack compared to a cell?(5)
Nucleus
organelles
cell surface membrane
cytoplasm
How do viruses replicate
Must be in a host cell
They attach to host cells via there attachment proteins which are complimentary to receptor proteins
they inject genetic material
cell replicates the viral nucleic acids and proteins which form more of the virus.
What are the 4 defence mechanisms in the body
Physical barrier
Phagocytosis
Cell mediated response (T Lymphocytes)
humoral response (B lymphocytes
How does phagocytosis happen?
The microbes are detected by chemicals
They are engulfed by the membrane.
phagosome forms
lysozyme containing hydrolytic enzyme fuses to phagosome
microbe is hydrolysed
indigestible matter is discharged
where can antigens be found and what are they?
Antigens are proteins or glycoproteins that appear foreign
They can be found on
the surface of a pathogen
on the cell surface membrane of other organisms of the same species
abnormal body cells
as a toxin
explain the humoral response
Every type of B cell produces a specific antibody
They secret antibodies onto their membranes
specific antigens may attach to the complimentary antibody on the B Cells
Helper T cells stimulate the division of B cells
Mitosis leads to a large population of plasma cells. These plasma cells will go to the blood stream and secrete identical antibodies
some B cells differentiate into memory b cells
What are the regions of an antibody and how many polypeptide chains are they made of
variable region
constant region
4 polypeptide chains ( 2 heavy and 2 light) joined by Disulphide bonds
where do antigens attach to antibodies
antigen binding site
