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topic 2 (new) Cheat Sheet (DRAFT) by

topic 2 (new) bc the other one was messy

This is a draft cheat sheet. It is a work in progress and is not finished yet.

Process of DNA replic­ation

DNA replic­­ation is a semi-c­ons­erv­ative process where the DNA molecule unwinds and unzips because of the enzyme DNA helicase so the hydrogen bonds between the bases break. The free DNA nucleo­­tides line up alongside each single DNA strand and hydrogen bonds form between the comple­­me­ntary bases. The enzyme DNA polymerase links the adjacent nucleo­­tides with phosph­­od­i­ester bonds in conden­­sation reactions to form new comple­­me­ntary strands. Overall, two DNA molecules are created.

Process of transc­ription

The DNA helicse unzips and unwinds the DNA at the gene that codes for the desired protein. The enzyme RNA polymerase then attaches to the DNA. The template strand is transc­­­ribed - an mRNA molecule is created using comple­­­m­e­ntary RNA nucleo­­­t­ides. Phosph­­­o­d­i­­ester bonds form between the RNA nucleo­­­tides of the mRNA strand. The mRNA moves out of the nuclear pores of the nuclear envelope.

Process of transl­ation

The mRNA molecule attaches to a ribosome. The mRNA binds to the small subunit so that 2 mRNA codons face the 2 binding sites of the larger subunit. A tNRA anticodon sequence comple­­­m­e­ntary to the mRNA codon sequence brings along a particular amino acid. Within the cytoplasm, free amino acids become attached to the correct tRNA molecules. Comple­­­m­e­ntary anticodon UAC hydrogen bonds to the start codon. The second codon faces the next binding site and the comple­­­m­e­ntary tRNA amino acid complex binds to it. A peptide bond forms between the 2 amino acids via a conden­­­s­ation reaction between the amine group of the amino acid and carboxyl group (COOH) of the next, forming a dipeptide. The tRNA returns to the cytoplasm where it can collect another amino acid 9. This process continues until a stop codon is reached. There are no anticodons to thee codons so no amino acids. Polype­­­ptide chain detaches from the ribosome.
 

Human lung adapta­tions

• Rate of diffusion is propor­­tional to surface area - alveoli have a large surface area.
• Rate of diffusion is propor­­tional to difference in concen­­tr­ation - breathing maintains a difference in gas concen­­tr­a­tions
• Rate of diffusion is propor­­tional to difference in concen­­tr­ation - blood flow maintains a difference in gas concen­­tr­a­tions
• Rate of diffusion is inversely propor­­tional to diffusion distance - walls of alveoli and capill­­aries are one cell thick
• Diffusion distance is reduced due to flattened cells forming alveoli and capillary walls
• Rate of diffusion is propor­­tional to diffusion constant - cell membranes are relatively permeable to non-polar gas molecules
Perfect exam answer (4-6 marks): The human lungs are adapted for gas exchange because the diffusion distance for gas exchange is reduced due to the flattened cells forming alveoli and capillary walls. The rate of diffusion is propor­­tional to the surface area because the alveoli have a large surface area for gas exchange. Furthe­­rmore, the walls of the alveoli and capill­­aries are one cell thick so the rate of diffusion is inversely propor­­tional to the diffusion distance and blood flow maintains a difference in gas concen­­tr­a­tions
NB: Fick's law states that the larger the surface area, difference in concen­­tr­ation and shorter the diffusion distance the quicker the rate. You need to remember this for these kinds of exam questions.

Difference between transc­ription and replic­ation

DNA Replic­ation
Transc­ription
• Replic­ation produces double stranded DNA molecules
• Transc­ription produces a single stranded RNA molecule
• Replic­ation involves DNA nucleo­tides
• Transc­ription involves RNA nucleo­tides
• Replic­ation uses DNA polymerase
• Transc­ription requires RNA polymerase
• Replic­ation produces identical copies
• Transc­ription produces a comple­mentary copy

Compare and constrast deletion & substi­tution

• Deletion could affect every codon but substi­­tution will only affect one codon.
• Deletion is more likely to affect the position of the start codon/stop codon and results in a different sequence of amino acids whereas substi­­tution may not affect the sequence of amino acids.
• Substi­­tution may code for the same amino acid due to the degenerate nature of the genetic code.

Subs. (repla­cement) and loss (deletion)

• loss causes whole amino acid sequence (beyond mutation) to change / cause frame shift / eq ;
• replac­ement only changes one { codon / amino acid / may not change the amino acid of third base / eq }
• number of amino acids remain the same with replac­ement
Note: subs. just means 'subst­itu­tion'.

Endocy­tosis and exocytosis

• both endocy­­tosis and exocytosis involve the usage of vesicles
• both endocy­­tosis and exocytosis involve energy from ATP
• endocy­­tosis involves substa­­nc­e­s­/m­­ole­­cules entering the cell
• exocytosis involes molecu­­le­s­/­su­­bst­­ances leaving the cell
• endocy­­tosis involves the formation of vesicles from the cell surface membrane
• exocytosis involves vesicles fusing with the cell surface membrane

Diffusion and active transport

• both diffusion and active transport move molecules through the phosph­­olipid bilaye­­r/cell surface membrane
• molecules can move through proteins in both diffusion and active transport
• diffusion occurs down a concen­­tr­ation gradient
• active transport occurs against a concen­­tr­ation gradient
• diffusion is a passive process that doesn't require ATP
• active transport does require ATP
 

CF stages

Remember this is for a healthy indivi­dual.
Remember this is for a CF sufferer.
1. Na+ is actively pumped across the basal membrane
1. Cl- is pumped into the cell across the basal membrane.
2. Na+ diffuses through sodium channels in the apical membrane
2. Cl- diffuses through the open CFTR channels.
3. Cl- diffuses down electrical gradient
3. Na+ diffuses down the electrical gradient into the mucus
4. Water is drawn out of cells by osmosis due to the high concen­tration in the fluid tissue
4. Elevated salt concen­tration in the mucus draws water out of the cell by osmosis.
5. Water is drawn out of the mucus by osmosis
5. Water is drawn into the cell by osmosis

Why is genetic screening used?

• to confirm diagnosis
• for testing embryos
• to identify carriers
 

Core practical 3

• indepe­ndent variable: the different temper­atures of water surrou­nding the beetroot
• dependent variable: transm­ission of light through the sample of water surrou­nding the segment
• control variables: age/sp­ecies of the beetroot, temper­ature, volume­/te­mpe­rature/ of solution, time beetroot is left in solution
• measur­ement of absorbance of solution using a colori­meter
• repeats at each temper­ature to calculate the permea­bility of the beetroot membrane