Cell Cycle And The Immune System Flashcards
Cell cycle in eukaryote
5
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
5
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
6
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
