Cell Cycle And The Immune System Flashcards
Cell cycle in eukaryote
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In multicellular organisms, not all cells keep their ability to divide.
Most of our cells differentiate to specialise e.g. red blood cell or white blood cell. The ones that do, stem cells, follow a process called the cell cycle.
The cell cycle starts consists of a period of growth and DNA replication, called interphase and a period of cell division, called mitosis.
Interphase is the longest phase in the cycle, normally longer than the whole of mitosis, unless the cell is rapidly dividing
. It is split into three separate growth stages. These are called G1,S and G2.
4 phases of cell cycle
Growth phase 1= The cell grows.Number of organelles increase.Proteins are made.ATP synthesised
Synthesis= synthesis of the DNA
Growth phase 2= The cell keeps growing,More proteins are made,ATP is synthesised
Mitosis= prophase, metaphase, anaphase, telophase
Homologous chromosomes
The same size
Shape ,and centromere is in the same place
Maternal from mum
Paternal from dad
Same genes on same loci ***
During interphase
DNA replicates
ATP synthesised
Organelles synthesised including centrioles
Proteins synthesised
DNA replication in interphase
Chromosomal DNA is replicated exactly by semi-conservative replication and the two pieces of DNA are held together by the centromere.
The two molecules of DNA held together are called sister chromatids.
If the copies are not copied accurately mutations may occur and daughter cells will not receive identical genetic material.
Importance of mitosis
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All organisms that need to produce genetically identical daughter cells.
Asexual reproduction - single celled organisms divide to produce daughter cells. E.g. paramecium. Multi-celled organisms may also divide asexually e.g. Hydra.
Growth - multicellular organisms grow by producing new extra cells that are genetically identical to each other and the parent cell.
Repair – tissues can be repaired e.g. skin after a burn, by making new cells.
Replacement - red blood cells and skin cells need to be replaced on an ongoing basis as they have limited lifetimes.
*cells replaced to repair tissue can’t repair cells
Phases of mitosis
Prophase = replicated chromosomes shorten and thicken (supercoil). Each chromosome consists of a pair of sister chromatids. Nuclear envelope breaks down and disappears. Nucleolus also disappear. centriole moves to opposite poles of the cell to form a spindle (protein threads). Metaphase = replicated (during interphase NOT during mitosis) chromosomes line up down the middle of the cell. Each chromosome is attached to a different spindle fibre by its centromere. Anaphase = the two chromatids of each chromosome are pulled apart from each other towards opposite poles of the cell. Identical sister chromatids are pulled to different poles by the shortening of the spindle fibres. Telophase = two new nuclei are formed. Sister chromatids reach poles and are now chromosomes. Spindle breaks down and disappears. Chromosomes uncoil and can’t be seen in a light microscope any more. Nuclear membranes start to reform around each set of chromosomes.
Cytokinesis
Animals
Plants
Cytokinesis= When the cell didvides. Occurs between telophase and interphase. Two new identical daughter cells.
In animals= Microtubles form a “draw string” inside the membrane which then fuses as it is pinched in.
In plants= Microtubules direct vesicles to the middle of the cell to form a cell plate which forms a new cell wall
New cell surface membrane is made on either side to enclose the two cells
Cause of cancer
if there’s a mutation in a gene that controls cell division, the cells can grow out of control which can lead to the formation of tumours. Tumours can develop in any organ of the body, but are most commonly found in the lungs, prostate gland (male), breast and ovaries (female), large intestine, stomach, oesophagus and pancreas.
A tumour becomes cancerous if
if it changes from benign to malignant. Malignant means that it has developed the ability to spread to other parts of the body. Benign means that it is growing but not spreading.
Cancer treatment
targeting and killing dividing cells by blocking part of the cell cycle. In this way the cell cycle is disrupted and so cell division - cancer growth, stops. Unfortunately, these treatments do not distinguish tumour cells from normal dividing cells, However, as tumour cells divide more frequently than normal cells the treatment is more likely to kill tumour cells. Normal body cells that rapidly divide such as hair producing cells are also vulnerable. This explains the hair loss frequently seen in patients under going cancer treatments.
Drugs used to treat cancer usually disrupt the cell cycle by
Preventing DNA from replicating.
Radiation and some drugs damage DNA. If severe DNA damage is detected the cell will self-destruct.
Inhibiting the metaphase stage of mitosis by interfering with spindle formation.
Preventing the synthesis of enzymes needed for DNA replication in S phase.
Types of defence
SPECIFIC DEFENCES: targeted against specific bacteria or viruses (and other cells or molecules that should not be in your body).
Involves:
B cells
T cells
NON-SPECIFIC DEFENCE: attacks anything in the body that shouldn’t be there.
Involves phagocytes: there are two kinds - neutrophils and macrophages.
Two types of phagocytes
Neutrophils =Shorty lived, die after engulfing bacteria
Multi lobed nucleus
Number rise as a result of infection
Macrophage=Long lived, survive after engulfing bacteria
Settle in lymph nodes, spleen and kidney
Important in specific immune response
Antigen presentation
Phagocytosis
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Chemical products of pathogens or dead and abnormal cells act as attractants, causing phagocytes (neutrophils and macrophages) to move towards the pathogen.
Phagocytes have several receptors on their cell surface membrane that recognise and attach to the antigen.
They engulf the pathogen to form a phagosome.
Lysosomes move towards the phagosome to fuse and form a phagolysosome.
Enzymes called lysozymes hydrolyse the pathogen into soluble products that are absorbed into the cytoplasm
Macrophages present the antigens to other white cells (neutrophils don’t).
T lymphocyte
Mature in the thymus
Cell mediated response
Immunity involving body cells
B lymphocyte
Mature in the bone marrow
Humoral response
Involves antibodies that are present in body fluids or ‘humour’
Cell mediated response and hum oral response
Booklet
Primary immune response
When a pathogen enters the body it takes time to produce cloned plasma be cells which secrete antibodies complimentary to the antigen
The antibody level in the blood will rise however the delay can result in the person suffering from the disease
once the pathogen has been eliminated the blood antibody level falls
specific memory B-cell remain in the body
Secondary immune response
If the pathogen re-invades memory B-cell clone rapidly and produce more antibodies at a faster rate
More plasma cells with the correctly shaped receptor will be produced more rapidly by clonal expansion
Antibodies
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Y shaped proteins that recognise and neutralise antigens
Produced by B lymphocytes
Made of 2 heavy and 2 light polypeptide chains with a specific binding site
Binding site is a sequence of amino acids that form a specific 3D shape
Ways antibodies are able to combat pathogens
Agglutination= forming antibody-antigen complexes, pathogens are held together in large clumps, macrophages and neutrophils can more easily engulf pathogens
Neutralisation= antigens which are toxins are rendered harmless if they are blocked by being bound to an antibody
Markers= stimulate phagocytes to engulf the bacterial cells to which they are attached
Monoclonal antibodies
Antibodies produced from a single group of genetically identical B cells
They are identical and specific to one antigen
They can be produced in the lab for treatment and medical diagnosis
Anti cancer drugs
Target cancer cells
Cancer cells have antigens called tumour markers
Monocolonal antibodies can be produced that will bond to the tumour marker
You can attach anti cancer drugs to the antibodies
Antibodies in medical diagnosis
Used as a tool in diagnosing diseases
Pregnancy testing
When a human embryo implants HCG is secreted and found in urine
Monoclonal antibodies which are specific to hcg are in the test and tagged with a blue bead
Direct Elisa
Collect a sample Add antibody with enzyme attached If antigen is present then antibody binds Wash to remove any unbound antibodies Add substrate complimentary to enzyme Coloured product formed of positive
Indirect Elisa
Antigen bound to the bottom of the well
Sample of blood added and any specific antigen will bind
Wash to remove any unbound antibodies
A second antibody with an enzyme attached is added
Wash to remove any that have not bound
Substrate added that will change colour if positive results
Active immunity
Immune system produces its own antibodies after being stimulated
Natural= results from individual becoming infected under normal circumstances, body produced its own antibodies
Artificial= involves inducing an immune response eg vaccine
Passive immunity
Introduction of antibodies from an outside source
Natural= from mother passed through placenta or milk
Artificial= injected with antibodies
Active v passive
Active Requires exposure to antigen Immune response takes a while Memory cells produced Long term protection
Passive Doesn’t require exposure to antigen Immediate protection Memory cell not produced Short term protection as antibodies get broken down
Vaccination
Deliberate exposure to antigen to activate immune response and memory B cells which provides immunity
Herd immunity
Difficulty of vaccines
Can fail in certain individuals
Pathogen may mutate so vaccine is no longer effective
Varieties of pathogen so cant create vaccine against them all
Vaccines ethical issues
Tested on animals
Testing on humans can be risky
Side effects
To be fully effective while population needs to be vaccinated
Monoclonal antibodies ethical issues
Involves use of mice
Have been a few deaths associated with their use
Antibiotics
Prevent bacteria from making a normal cell wall
What is HIV
Virus that affects the human immune system it’s eventually leads to AIDS which is where the immune system eventually fails
How HIV works
HIV infected and kills help at T cells which acts as the host cell for the virus. Without helper T-cell is Amy and system is unable to respond effectively
HIV initial infection
During the initial infection HIV replicates rapidly and the infected person may develop before flu like symptoms
After this period replication drops to a lower level and the virus remains dormant and the person will not have any symptoms
HIV replication
- The attachment protein attaches to receptor molecule on the cell membrane of the host helper T-cell
- The capsid is released into the cell where it un coats and releases the genetic material into the cells cytoplasm
- Reverse transcriptase makes a complimentary strand of DNA from the viral RNA template
- Double-stranded DNA is made and inserted into DNA
- Host cell enzymes are used to make viral proteins from the viral dna
- The viral proteins are assembled into new viruses and go to infect other cells
Which cells don’t undergo cytokinesis
Muscle
Cells
How many chromosome in human
46
23 pairs
Mitosis definition
Division of the nucleus
Centrioles
Help to organise the assembly of spindle which is involved in chromosome movement in mitosis
Required practical
Toluidine blue/ acetic orcein stain used to stain nucleic acid
Sample is heated in acid which breaks down middle lamella which bonds plant cells together. This allows sample to be flattened
Flattens so is one cell thick and light can pass through and chromosome can be seen
Avoid twisting when flattening so cells maintain original position
Mitotic index=
No. Of cells in mitosis/ total no of cells
