Longer processes last Flashcards
(27 cards)
Describe the process of protein synthesis.
Protein synthesis involves two main stages: transcription and translation. In transcription, DNA is used as a template to form pre-mRNA in the nucleus. The enzyme RNA polymerase binds to DNA and joins RNA nucleotides to form pre-mRNA. This pre-mRNA undergoes splicing to remove introns, forming mRNA. The mRNA leaves the nucleus and attaches to a ribosome. In translation, tRNA molecules bring amino acids to the ribosome, matching their anticodons to codons on the mRNA. The ribosome joins amino acids with peptide bonds, forming a polypeptide chain.
Explain the process of DNA replication.
DNA replication is semi-conservative. The enzyme DNA helicase unwinds the double helix and breaks hydrogen bonds between bases. Each strand acts as a template. Free DNA nucleotides bind to complementary bases via hydrogen bonding. DNA polymerase joins the nucleotides to form a new strand via phosphodiester bonds. Each new DNA molecule contains one original and one new strand.
Describe the stages of mitosis.
Mitosis has four stages: Prophase, Metaphase, Anaphase, and Telophase. In Prophase, chromosomes condense and spindle fibers form. In Metaphase, chromosomes align at the cell equator. In Anaphase, sister chromatids are pulled apart to opposite poles. In Telophase, nuclear membranes reform and chromosomes decondense. Cytokinesis then divides the cytoplasm, forming two identical daughter cells.
Describe meiosis and how it causes genetic variation.
Meiosis involves two divisions. In Meiosis I, homologous chromosomes pair and are separated. Crossing over occurs where sections of DNA are exchanged between chromatids. In Meiosis II, sister chromatids are separated. Independent assortment and crossing over cause genetic variation.
Explain the co-transport of glucose in the ileum.
Sodium ions are actively transported out of epithelial cells into the blood via a sodium-potassium pump. This creates a concentration gradient for sodium to enter the cell from the ileum via facilitated diffusion. Sodium brings glucose with it via a co-transporter protein. Glucose then moves into the blood by facilitated diffusion.
Describe the immune response to a pathogen.
The immune response involves non-specific and specific defenses. First, phagocytes engulf pathogens. Then, T cells bind to antigens on antigen-presenting cells, activating other immune cells. B cells are activated and divide into plasma cells, which secrete antibodies. Memory cells are produced for a faster secondary response.
Explain gas exchange in fish using the counter-current system.
Fish gills use a counter-current system where water and blood flow in opposite directions. This maintains a steep concentration gradient along the entire length of the gill, allowing efficient oxygen diffusion into the blood.
Describe osmosis in plant cells.
Osmosis is the movement of water from a region of higher water potential to lower water potential across a partially permeable membrane. In plant cells, water entering makes the cell turgid. If water leaves, the cell becomes flaccid and may plasmolyze if too much water is lost.
Explain the role of the Golgi apparatus in protein transport.
The Golgi apparatus modifies and packages proteins received from the rough ER. It adds carbohydrates to form glycoproteins and packages them into vesicles for transport to the cell surface or other locations.
Explain genetic crosses involving codominance.
In codominance, both alleles in a heterozygote are expressed equally. Genetic crosses use uppercase letters with superscripts to distinguish alleles. The phenotype shows both traits. Punnett squares are used to predict ratios in offspring.
Where does light dependent reaction happen?
- Thylakoid membrane where folded membranes contain photosynthetic proteins and electron carrier proteins which are embedded within these membranes, both being involved in the LDR.
Where does the Light independent reaction happen?
- Stroma (Fluid centre which contains enzymes involved in the light independent reaction)
4 key stages of Light Dependent Reaction
1) Photolysis
- Light energy is absorbed and splitts water into oxygen hydrogen and electrons
- H+ ions are picked up by NADP to form NADPH and this is used in the LIR
- The electrons pass along the electron carrier proteins
- Oxygen is used for respiration or diffuses out of the leaf through the stomata.
2) Photoionisation
- Light energy is absorbed by chlorphyll, electrons gain energy and are excited, causing electrons to leave to another energy level, leaving the cholorphyll
- Some of the energy from the released electrons is used to make ATP and reduced NADP in chemiosmosis.
3) Chemiosmosis
- As electrons move, they release energy, which pumps protons into thylakoid lumen from the stroma via proton pump.
- Protons can move via facilitated diffusion to the stroma via an ATP synthase and this is the reason we have ATP production.
- Protons combine with co-enzyme NADP and becomed reduced.
4) Production of ATP and reduced NADP
Light independent reaction
- CO2 reacts with RuBP to form 2 GP molecules.
- This reaction is catalysed by the enzyme Rubisco.
- GP is reduced to TP using the energy from ATP.
- TP is converted into useful organic molecules or regeneration of RuBP.
What happens in glycolysis?
- Occurs in the cytoplasm
- Glucose converted to glucose phosphate (by ATP hydrolysis)
- Glucose phosphate converts into TP molecules.
- Redox reaction converts TP into 2 Pyruvate molecules via redox reactions. (reduction of 2 NAD molecules, using 4 ATP molecules)
Anaerobic respiration in animals and plants
ANIMALS
- Pyruvate is converted to lactate in a redox reaction of NADH.
- Regeneration of NAD so glycolysis can still continue.
- Lactate can damage cells.
PLANTS YEAST
- Pyruvate converted to ethanal, producing CO2 in the process, then ethanal is converted into ethanol in a redox reaction/
Link reaction
- Acetate is formed when Pyruvate loses carbon
- NAD -> NADH
- Acetyl coA when acetate combines with coA.
Matrix
- Acetyl coA reacts with a 4C carbon compound to form a 6C carbon compound.
- Redox reactions lead to 2 CO2, 3 NADH and 1 FADH2 and 1 ATP.
Oxidative phosphorylation in respiration
- Hyrodgen atoms released from reduced coenzymes
- Hydrogen atoms split in hydrogen ions and electrons.
- Electrons move down ETC
- Energy lost at each carrier is used to pump H+ ions into itnermembrane space, creating favourable conc gradient for diffusion of H+ into matrix via ATP synthase.
Oxygen as final electron acceptor but why?
- Oxygen accepts H+ ions and low energy electrons to form water
- If it didn’t happen, electron transport chain would stop and no pumping of hydrogen ions.
No diffusion of H+ ions so no ATP produced.
What happens when little O2 available?
- Too many hydrogen ions not being accepted by oxygen
SO - Respiration is stopped back to glycolysis as we need to remove the hydrogen atoms from NADH in oxidative phosphorylation to produce NAD, which is needed for glycolysis to continue.
Outline ultrafiltration
- First process of osmoregulation
- Efferent arteriole smaller in diamter than the afferent arteriole so hydrostatic pressure in the glomerular capillaries increases.
- Small molecules forced through 3 layer filter made out of capillary endothelium, basement membrane and podocytes.
- Proteins, RBCs too large
- Forms glomerular filtrate
Outline selective reabsorption
- Reabsorption of useful substances.
- They pass back into blood capillaries wrapped around the proximal convoluted tubule.
- Done by co-transport with sodium ions.
- Reabsorption lowers the water potential of blood so water moves out of the PCT into the capillaries by osmosis.
