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genes and health Cheat Sheet (DRAFT) by

exam answers type deal for t2

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

Genetic screening

Amnioc­entesis
Chrionic Villus Sampling
NIPD (non-i­nvasive prenatal diagnosis)
PGD (preim­pla­ntation genetic diagnosis)
• Done at 15-17 weeks of pregnancy
• Done at 8-12 weeks of pregnancy
• Done at 7-9 weeks of pregnancy
• N/A (for when it's done)
• A needle is placed into the amniotic fluid to collect foetal cells that have fallen off the placenta or foetus
• A small sample of the placenta is taken either through the wall of the abdomen or through the vagina
• DNA fragments are taken from the mother's blood plasma (most of it is cffDNA) for analysis
• Couple undergo IVF (30% success rate for women under 35)
• Allows the parents to make informed choices about future treatment, prepares parents for a child with a disease, gives the parents option for abortion.
• N/A
• Less traumatic procedure
• Only implants healthy embryos
• 1% risk of miscar­riage
• Claimed 1-2% risk of miscar­riage
  
• Procedure involving IVF can be regarded as unethical because the embryos are discarded, emotio­nally traumatic.
• Invasive method
• Invasive method
• Non-in­vasive
• Non-in­vasive

Processes for topic 2

Process of DNA replic­ation
Process of transc­ription
Process of transl­ation
Semi-c­ons­erv­ative replic­ation is 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.
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.
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.

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

Cystic Fibrosis

Respir­atory system
Reprod­uctive system
Digestive system
The cilia in the lungs of a CF sufferer would struggle to beat/move mucus out of the lungs due to the mucus being abnormally thick and sticky (viscous). This would mean that there is an increased risk of lung infect­ions.
Males: The sperm cannot leave the testes because the vas deferens is blocked by the highly viscous mucus. This means that the vas deferens is absent so sperm cannot pass through.
The pancreatic enzymes cannot enter the intestines because the pancreatic duct is blocked by the thick mucus. Due to digestion being less efficient, a high energy diet is required. Pancreatic enzymes that are trapped behind the thick mucus damage the pancreatic cells (e.g. ones that produce insulin) and cysts form in the pancreas as a result. Diabetes may also occur.
Thicker mucus is produced because the chloride ions cannot leave the cell through the CFTR protein channel and sodium ions don't move out of the cells so water moves into cells by osmosis.
Females: A mucus plug develops in the cervix which stops the sperm from reaching the egg so female sufferers with CF are less likely to become pregnant and are more likely to be infertile.
The thickness of the mucus depend­s/v­aries on the mutation because different mutations will have different effects on the protein produced and the chloride ion transport is affected by the extent of changes to the CFTR protein.

CP 4 - Enzymes

Variables
Controls (same)
Repeats (why?)
Results
• IV: concen­tration of the enzyme
• Temper­ature (C)
• To compare optimum temper­ature for enzyme­-su­bstrate complex to form
• As the temper­ature (C) gets higher, the active site of the enzyme denatures faster.
• DV: time in seconds taken for the enzyme to break down substrate (using a stopclock)
• Volume of enzyme (cm3)
 
• Volume and concen­tration of the substrate
 
• pH

Mononu­cle­otide diagram

Dipeptide diagram

You need to also draw water on. Remember, the O is on top and 2 Hs at the bottom.

Definition of a recessive allele

Recessive alleles are a different form of a gene and have the same two alleles (e.g. rr) and they are not expressed in the presence of a dominant allele. They are in the same locus of a chromosome but are a different form of a gene.

Definition of a gene

A gene is a sequence of bases on a DNA molecule that codes for a sequence of amino acids in a polype­ptide chain

Definition of template

Where the RNA nucleo­tides attach for transc­ription

Definition of an allele

A different version of a gene found on a chromo­some.

Structure of an amino acid

You need to know this for the exam since you have to draw it out.

Definition of a dominant allele

A dominant allele is the one that is expressed in the same phenotype (e.g. RR) and is found on the same locus of a chromo­some.
 

Compare and constract diffusion + 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 whereas active transport occurs against a concen­tration gradient
➼ diffusion is a passive process that doesn't require ATP whereas active transport does require ATP

Compare and constract endocy­tosis + exocytosis

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

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.

Sim + diff between fac. diffusion and AT

Simila­rity: Both facili­tated diffusion and active transport use carrie­r/t­ran­sport proteins
Differ­ence: Facili­tated diffusion is a passive process that doesn't require ATP whereas active transport uses ATP for energy.
   

CP 3 - Beetroot practical

Variables
Controls (how?)
Repeats (why?)
Results
• IV: temper­ature of the water (Celsius)
• Volume of distilled water
• To calculate the permea­bility of the beetroot membrane
• As temper­ature of the water increases, the beetroot permea­bility decreases.
• DV: % transm­ission of light through resulting solution using a cuvette
• Time left in water
 
• Size of beetroot piece

Why is genetic screening used?

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

tRNA and mRNA

tRNA
mRNA
• folded­/clover leafed
• straight folded chain
• size/l­ength of tRNA is constant
• size/l­ength of mRNA is variable
• tRNA has antico­don­s/amino acid binding sites
• mRNA has codons
• both contain RNA mononu­cle­otides
• both are single stranded

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

Globular and fibrous proteins

• Both globular and fibrous proteins are chains of amino acids joined by peptide bonds
• Both globular and fibrous proteins contain hydrog­en/­dis­ulf­ide­/ionic bonds
• Globular proteins have hydrop­hillic groups on the outside (soluble)
• Fibrous proteins have hydrop­hobic groups on the outside (insol­uble)
• Globular proteins have tertiary or quaternary structures
• Fibrous proteins have little to no tertiary structure
• Globular proteins are folded into compact shapes
• Fibrous proteins have long chains

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.