Outside spec knowledge

Endosymbiotic theory

• According to endosymbiotic theory mitochondria and chloroplasts originated as free-living prokaryotes that were once engulfed by larger ancestral cells. This is thought of due to their double membrane - their inner membranes resembles that of prokaryotes, whereas the outer membrane likely originated from the host cell’s membrane during engulfment.

• Mitochondria have a double membrane, the inner of the two membranes is folded to form extensions known as cristae
  Cristae provide a larger surface area for enzymes and other proteins involved in respiration to attach, for example ATP synthase. Impact of increased ATP synthase is it increases the efficiency of ATP production (condensation reaction ADP + Pi --> ATP). ATP used as an energy source for vital reactions and processes in the body, for example active transport (of Na+ ions through Na+/K+ pump in the ileum)

• Chloroplasts are double-membrane-bound organelles, and inside they contain the grana – which are stacks of up to 100 flattened membrane sacs called thylakoids.
  The stacking of thylakoids in the grana increases the surface area of the thylakoid membrane, which provides a larger surface area for the attachment of chlorophyl. which therefore means more chlorophyll can be embedded. Chlorophyll is a photosynthetic pigment and therefore more chlorophyll will increase the rate of photosynthesis, therefore increasing glucose production as a product of this reaction. Glucose can be stored in the plant as starch for an energy source, or used as a respiratory substrate. This is vital to provide energy for processes such as the active transport of sucrose from source cell to the sieve tube element in translocation

Phosphoanhydride bonds

ATP is a useful energy source within the body due to phosphoanhydride bonds, which form between the three phosphates in ATP. These are covalent bonds (formed in a condensation reaction) that are very high energy, meaning that when broken, they release large amounts of energy to be used in cellular processes. This is important to metabolic reactions as ATP is not a long-term store of energy, but a short term, immediate energy source – particularly useful in processes such muscle contraction or the regulation of body temperature. This is only possible through the involvement of the ions hydrogen and phosphate. 

Guard cells

• double check this card

• In response to an increase in light intensity, ATP-powered proton pumps in the guard cell surface membranes actively transport hydrogen (H+) ions out of the guard cell. This active transport occurs against the concentration gradient and therefore requires energy released from the hydrolysis of ATP. This process establishes a comparatively greater negative charge inside of the guard cells in comparison to the outside, where this difference in charge across the membrane creates an electrical gradient. Therefore, channel proteins in the guard cell surface membrane transport positively charged K+ ions down the electrochemical gradient (via facilitated diffusion) into the guard cells. This increase of K+ ions increases the solute concentration inside the guard cells, thus lowering the water potential. Water moves into the cells by osmosis through aquaporins in the guard cell surface membrane primarily into the vacuoles and cytoplasm. This increases the turgor pressure of the guard cells, and the thin outer walls bend more easily than the thicker inner walls due to bands of cellulose microfibrils. Therefore, the guard cells become curved and the stomata open.

Acetylcholinesterase

An example of the induced fit model of enzyme action, where the active site of acetylcholinesterase undergoes a slight conformational change once bound to acetylcholine to become more complementary. This is important to break down neurotransmitters in the synaptic cleft, stopping nervous impulses from continuing indefinitely. The induced fit model increases the efficiency and specificity of the enzyme for this function 

Sickle cell anaemia 

Substitution point mutation in the HBB gene (which codes for the b-globin chain in haemoglobin). DNA base substitution of adenine for thymine, which results in valine amino acid instead of glutamine. Valine is hydrophobic and causes b-globin chains to stick together under low oxygen conditions – distortion of RBCs into sickle shape, which means they are less flexible and more likely to block capillaries

• Anaemia - a mutation in the HBB gene of haemoglobin results in less oxygen binding to RBCs and therefore less oxygen reaching the respiring tissues - symptoms such as fatigue or shortness of breath when exercising  

Synaptic transmission

• Disruption in synaptic transmission can lead to neurological disorders such as Alzheimer’s and Parkinson’s disease, which impair cognitive and motor functions

• Cognex is a treatment for Alzheimer’s, which acts as a reversible inhibitor of acetylcholinesterase, meaning that less acetylcholine is hydrolysed into acetate and choline and reuptaken into the presynaptic neurone. Therefore there is more acetylcholine available in the synapses, which means more acetylcholine can bind to receptors on the post synaptic neurone

Cholera

• transport of Cl- ions into the intestinal lumen, lowers water potential, creating a water potential gradient for more water to move via osmosis into the intestine - can cause diarrhoea and lead to severe dehydration

Edema in pregnancy

• Swelling, common in pregnancy particularly in the legs, ankles and feet

Spider venom

• Spider venom can cause sodium ion channels to remain open, preventing them from closing. Continuous influx of sodium ions into the neurone means that the post-synaptic membrane remains depolarised. As such, the neurone cannot repolarise effectively and produce a new action potential - causing muscle paralysis