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Question 1

cells are robust. explain what this means

Answer 1

1) Robustness: the ability of a cell to maintain performance and function in the face of internal and external perturbations.2) Cells are dynamic and are therefore able to adapt to changes in their environment. In addition there is redundancy in cells and they are therefore fault tolerant.-Estimated that around 40% of metabolic reactions in bacteriaand yeast can be individually removed without impacting the function of the cell.

Question 2

describe how a fever during an infection can help the immune response.

Answer 2

Fever during infection can help the immune response by:1) Increased movement ofwhite blood cells2) stimulates your immune system into producing more white blood cells (T cells), antibodies, and a protein called interferon, all of which work to protect your body against harmful microorganisms.3) Enhanced rate of phagocytosis

Question 3

At higher temperatures cells encounter problems and become stressed. list some of the problems a cell might encounter due to an increase in temperature.

Answer 3

1) Most enzymes are optimised to work at 37°C. 2) The cell membrane becomes much more fluid. functions of membranes affected by heat.3) Proteins don’t fold properly.

Question 4

explain how membranes respond to heat

Answer 4

1) Change lipid composition of the membrane:- More saturated fatty acids : makes the membrane more viscous- Change cholesterol levels : this makes the membrane more stable (unsaturated fatty acids make the membrane more fluid which is the response for cold temperatures)

Question 5

what are heat shock proteins?

Answer 5

1) Heat shock proteins are a group of proteins that are produced when a cell is exposed to elevated, sub-lethal temperatures.2) These proteins protect the cell if it is subsequently exposed to what would have been lethal temperature rises.3) They increase in expression in response to other stresses such as deprivation of oxygen or nutrients.4) Their main function is to help proteins fold properly so that they can then function properly.

Question 6

outline the problems cells encounter due to cold temperatures.

Answer 6

1) Slow enzyme reactions2) Rigid & viscous membranes3) Ice crystals

Question 7

outline how membranes respond to cold temperatures

Answer 7

1) Change lipid composition of the membrane:- More saturated fatty acids- makes membrane more fluid - Change cholesterol levels- makes the membrane more stable

Question 8

what is the function of glycoproteins & glycolipids?

Answer 8

1) Proteins with carbohydrates attached ( occurs in Rough ER) are glycoproteins and the process of attaching the sugar is called glycosylation – a post-translational modification. A glycosidic bond links a carbohydrate to the side chain of the amino acids asparagine (N-linked) or to the side chain of serine or threonine (O-linked).2) Many glycoproteins are present in the plasma membrane with the carbohydrate region presented outside the cell.3) The attached sugars function to stabilise the protein structure in the extracellular environment therefore offer some protection from the environment4) Glycolipids are also present in the plasma membrane and have similar protective functions

Question 9

outline the benefits of Antifreeze glycoproteins

Answer 9

1) glycoproteins are used by Antarctic fish to stop them freezing. (Can stop ice crystal formation down to -2 C)2) These biological antifreezes have important medical applications where low temperature storage is required and ice crystal formation is damaginge.g. including improved protection of blood platelets and human organs at low temperatures.

Question 10

what is chitin?

Answer 10

1) structural carbohydrate 2) Carbohydrates can be protective in many ways.3) Can be combined with other substances to create a harder material (e.g. calcium carbonate in crustaceans, sclerotin in beetles).

Question 11

how do low oxygen conditions occur in the body?

Answer 11

1) Oxygen (and nutrient) concentration decreases quickly as the distance from blood vessels increases.2)Cells are usually within 0.5 mm of a blood vessel. Hypoxia (low oxygen) can set in at 150 µm from a blood vessel.-Oxygen is essential in ATP synthesis through its role as an electron acceptor in the electron transport chain.This accounts for 90% of the total oxygen uptake in most cells.Low oxygen levels are therefore extremely toxic to cells, leading them to die through necrosis.

Question 12

Explain how Hypoxia can occur

Answer 12

1) when environmental oxygen levels are low (e.g. at high altitude), 2) in premature babies (where the lungs are not properly developed)3) following poisoning (e.g. carbon monoxide, cyanide) because of anaemia (low oxygen carrying capacity in blood)local hypoxia can occur because of:1) Ischaemia (blood supply is cut off) following heart attacks and strokes2) Cancer (tumour growth collapses blood vessels)

Question 13

outline the cellular response to hypoxia

Answer 13

1) Cells have special oxygen sensing enzymes that detect hypoxia2) The oxygen sensors activate a range of transcription factors that move to the nucleus and alter gene expression3) The cell cycle stops (arrested at G1 phase)4)The cell switches to glycolysis and anaerobic metabolism to produce ATP5) There is rapid down-regulation of protein synthesis

Question 14

what is angiogenesis?

Answer 14

1) making new blood vessels2) In response to hypoxia, cells activate a range of hypoxia response genes.3) Many of these genes are growth factors (including VEGF and FGF) that stimulate cells in the nearby blood vessels to branch off, proliferate and move towards the hypoxic cell, thus delivering oxygen to the deprived area.

Question 15

outline how quiescence allows cells to survive nutrient deprivation

Answer 15

1) Quiescence is a state of reversible cell cycle arrest that can grant protection against many environmental stresses, including nutrient deprivation and starvation. 2) Also helps cells in low temperature and low oxygen environments 3) Cellular quiescence is often associated with a low metabolic state characterized by a decrease in glucose uptake and glycolysis, reduced protein synthesis rates and activation of autophagy as a means to provide nutrients for survival. 4) If the cell cycle arrest is not reversible the cells are said to be senescent.

Question 16

outline how autophagy allows cells to survive nutrient deprivation.( autophagy -a normal physiological process in the body that deals with destruction of cells in the body)

Answer 16

1) Autophagy is a major protective mechanism that allows cells to survive in response to multiple stresses, including nutrient deprivation and starvation.2) During autophagy, cells form double-membraned vesicles, autophagosomes, that isolate organelles, proteins, or portions of the cytoplasm for delivery to the lysosome.3) The membrane to form autophagosomes comes from existing organelles such as the ER, Golgi, plasma membrane or mitochondria.4) This allows rapid formation of autophagosomes in response to stress. 5) Lysosomes are organelles that contain a variety of powerful degradative enzymes. 6) Fusion of lysosomes with autophagosomes leads to degradation of the contents. 7) This allows cells to eliminate damaged or harmful components and recycle their constituents to maintain nutrient and energy homeostasis

Question 17

outline how proteasomes allow cells to survive nutrient deprivation

Answer 17

1) On a smaller scale to autophagy, the proteasome is also able to recycle cellular components.2) Proteasomes are multi-protein complexes that are able to degrade unwanted or damaged proteins, effectively recycling the amino acids to allow for more protein synthesis.3) It plays an important role in the general stress response including heat shock, infection and oxidative stress by degrading damaged or misfolded proteins proteins.

Question 18

list the damaging and toxic environments cells can be exposed too.

Answer 18

1) Radiation (especially UV light)2) Free radicals and oxidative stress3) Toxins and poisons (from bacteria, food etc)-These toxic agents can cause a wide variety of damage to the cell, so the cell needs a flexible system for both protecting itself and for repairing the damage.

Question 19

explain how highly reactive oxygen species are created.

Answer 19

1) The process of producing ATP through the electron transport chain relies on oxygen as the ultimate electron acceptor.2) In this last step oxygen accepts four electrons. Sometimes this doesn’t work properly and highly reactive oxygen species are created.

Question 20

explain how highly reactive oxygen species can damage cells.

Answer 20

1) Reactive oxygen species (ROS), in particular the hydroxyl radical, can react with all biological macromolecules including lipids, proteins, nucleic acids and carbohydrates.2) The initial reaction generates a second radical, which in turn can react with a second macromolecule to continue the chain reaction. 3) ROS modify both the structure and function of proteins and can lead to cross-linking or fragmentation of proteins. 4) Modification of individual nucleotide bases, single-strand breaks and cross-linking are the typical effects of reactive oxygen species on nucleic acids.

Question 21

outline the range of anti-oxidant defences that help protect a cell from damage

Answer 21

1) Glutathione is the major anti-oxidant in cells. It is synthesised in high amounts in cells. In its reduced form it readily donates electrons to reactive oxygen species, forming more stable molecules.2) Superoxide dismutases are enzymes that convert highly reactive superoxide free radicals (O2-) to less reactive hydrogen peroxide (H2O2).3) Catalase (located in peroxisomes) then converts hydrogen peroxide to water and oxygen

Question 22

What are drug transporters?

Answer 22

1) Transmembrane proteins that use ATP to transport substances across membranes.2) Found in high concentrations in the blood-brain barrier, hepatocytes in the liver and in stem cells.3) They can transport a wide range of substances, including toxins and drugs preventing damage.

Question 23

describe what happens during DNA damage response

Answer 23

1) DNA damage is detected2) Cells stop going through the cell cycle3) DNA repair is initiated4) If the DNA damage is too extensive the cell undergoes apoptosis-Damaged DNA must be repaired or mutations will be formed.

Question 24

Cells must be able to cope with fluctuations in their external environment. list some of the fluctuations they may encounter.

Answer 24

1) temperature2) pH3) nutrients4) oxygen5) UV light6) pathogens & toxins7) signals such as hormones, neurotransmitters etc-Beyond a certain threshold these changes are called stresses and the cell’s response to this stress determines whether it continues to function and survive

Question 25

During the response to sub-lethal stress the cells undergo rapid changes to their metabolism and protect themselves against damage. list some cellular changes that helps the cell survive

Answer 25

1) Changes in membrane composition2) Switch to anaerobic metabolism3) Increased antioxidants4) Increased drug transporters5) DNA repair6) Quiescence7) Autophagy

Question 26

explain what happens when cells ignore signals.

Answer 26

1) Strict control over cells is required in order for the organism to function correctly.2) When this control goes wrong we call the disease cancer.3) In cancer, cells ignore signals from other cells and start proliferating without any control or restraint.4) Eventually they lose social connections and move away from their original tissue5) DNA is constantly being damaged and repair is not perfect therefore mutations occur. cancer is therefore more or less inevitable and just a matter of time in most multi-cellular organisms.6) A cell’s defences are designed to delay cancer as long as possible: Antioxidants, DNA repair, apoptosis, extracellular matrix

Question 27

what are cell cycle checkpoints?

Answer 27

Cell cycle checkpoints are control mechanisms in eukaryotic cells which ensure proper division of the cell.1) G1: DNA damage checkpoint- entrance into S phase is blocked if genome is damaged 2) S phase - DNA damage checkpoint- DNA replication halted if genome is damaged 3) G2: entrance into M is blocked if DNA replication is not complete 4) M phase - anaphase blocked if chromatids are not properly assembled on mitotic spindle.