Biology Topic 2 Flashcards
(22 cards)
How are alveoli adapted for efficient gas exchange?
Large number of alveoli creates large surface area for diffusion.
Alveolar epithelium and capillary endothelium both one cell thick, giving a short diffusion distance.
All alveoli have good supply of blood from capillaries, which constantly take away O2 and bring CO2, maintaing the concentration gradient.
What is Fick’s law?
Rate of diffusion ∝ surface area × concentration difference/ thickness of diffusion surface
Fick’s Law Equation?
Rate = P × A × (c1-c2) ÷ T
P= permeability constant
A= surface area
(C1-C2) = concentration difference
T= thickness of diffusion surface
Describe structure of a cell membrane.
Phospholipid bilayer: hydrophilic phosphate heads face out towards water on either side of membrane. Hydrophobic fatty acid tails face inwards.
Also contains:
Glycolipids and glycoproteins for cell recognition
Channel and carrier proteins for facilitated diffusion
Cholesterol to control membrane fluidity
Evidence for Fluid Mosaic model.
Improved EM techniques showed bilayer of phospholipids.
New methods for analysing proteins showed they were ranged randomly in the membrane.
Mouse cell fused with human cell. Membrane proteins from mouse and huma intermixed completely. Proving membrane was fluid.
Facilitated Diffusion
Passive - doesn’t require ATP
Carrier proteins: move large molecules in and out of cell.
1. Large molecule attaches to carrier protein in membrane.
2. Carrier protein changes shape.
3. Large molecule released on opposite side of the cell.
Channels proteins: form pores in membrane for charged particles to diffuse through. Different channel proteins facilitate the diffusion of different charged particles.
Active Transport
Active- require ATP
Same as carrier proteins in facilitated diffusion but require ATP to be hydrolysed to provide energy to move molecule AGAINST its concentration gradient
Exocytosis and endocytosis
Exocytosis: Some substances made in cell need to be released. Vesicles containing these substances pinch off from the golgi. They fuse with the membrane and are either released outside cell or become part of the membrane. This requires ATP.
Endocytosis: Some molecules are too large for carrier proteins. Instead a part of the cell membrane surrounds them. This part of the membrane then pinches off to form a vesicle inside the cell containing the ingested substance. Requires ATP.
How could you investigate the affect of temperature on membrane permeability?
- Use scalpel to cut 5 1cm³ pieces of beetroot.
- Pipette 5cm³ distilled water into 5 test tubes.
- Place the test tubes into water bath at 5 different temperatures. E.g. 10, 20, 30, 40 and 50 degrees Celsius.
- Place the 5 pieces of beetroot into the test tubes and leave for an equal length of time e.g. 10 minutes
5.Remove pieces of beetroot to leave just liquid.
- Set up a colorimeter and zero it with distilled water.
- Pour the liquid from test tubes into 5 cuvettes and measure absorbence using colorimeter.
- The higher the absorbance, the higher the permeability as more pigment has leaked out.
Describe the 4 structural levels of proteins.
- Primary structure- the amino acids in the polypeptide chain.
- Secondary structure- hydrogen bonds form between the amino acids. Causing the protein to fold in beta pleated sheet or coil into alpha helix.
- Tertiary structure- bonds formed between residual groups on amino acids. Such as ionic bonds, hydrogen bonds, disulfide bridges and hydrophobic and hydrophilic interactions.
- Quaternary structure- several polypeptide chains held together by bonds
Globular and fibrous proteins
Globular: compact proteins made up of multiple polypeptide chains. Coiled so hydrophilic part faces outwards, making it soluble. As soluble, can be easily transported in fluids. E.g. haemoglobin
Fibrous: made of long, insoluble polypeptide chains. Held together by lots of bonds so strong. This makes them often used in supportive tissue. E.g. collagen.
How could you measure how fast production is made in enzyme-controlled reaction?
- Set up apparatus with upside measuring cylinder in jug of water to collect oxygen.
- Add hydrogen peroxide and different concentrations of catalase into boiling tube and attach delivery tube.
- Record the volume of oxygen produced every 10 seconds for 1 minute.
- Repeat at each concentration and calculate a mean.
- Plot volume O2 against time and draw tangent to calculate initial rate.
- Compare initial rates at different concentrations.
How could you measure rate of substrate removal in an enzyme-controlled reaction?
- Mix starch and iodine with different concentrations of amylase.
- Start stopwatch and measure absorbance every 10 seconds with a colorimeter.
- Repeat and calculate mean for each concentration.
- Plot absorbance against time and draw tangent to find initial rate.
- Compare rates across starch concentrations.
Describe transcription.
- RNA polymerase binds to promoter region of DNA.
- Hydrogen bonds between bases in the DNA molecule break and the DNA double helix unwinds.
- The template strand is used as a copy as RNA polymerase lines up free RNA mononucleotides with bases complementary to the template strand.
- RNA mononuleotides joined together by phosphodiester bonds, catalysed by RNA polymerase.
- Hydrogen bonds in DNA molecule reform and it rewinds into double helix.
- RNA polymerase stops making RNA when it reaches a stop codon.
- After pre-mRNA has been spliced, mRNA exits the nucleus via a nuclear pore.
Describe splicing of pre-mRNA
Pre mRNA contains coding regions (exons) and non-coding regions (introns). During splicing introns are removed and exons are joined together. Exons can also be removed and joined in different combinations, meaning one gene can code for multiple proteins.
Describe translation
- mRNA attaches to a ribosome.
- tRNA carrying amino acid binds to mRNA with its anticodon by complementary base pairing.
- 2nd tRNA attaches to the next codon in same way.
- Amino acids attached to tRNA are joined by a peptide bond in a condensation reaction. The 1st tRNA molecule then moves away, leaving its amino acid.
- Process continues, producing a polypeptide until a stop codon is reached.
- Polypeptide moves away from ribosome.
DNA replication
- The enzyme DNA helicase breaks the hydrogen bonds between bases on the 2 polynucleotide strands. Making the helix unwind to form 2 separate strands.
- Each original single strand acts as a template for a new strand. Complementary base pairing means that free floating DNA nucleotides are attracted to complementary exposed bases.
- Condensation reactions join the nucleotides of the new strands, catalysed by DNA polymerase. Hydrogen bonds form between the bases on the new and original strands.
- Each new molecule contains one strand from original DNA molecule and one new strand.
How does the Meselson and Stahl experiment prove that DNA replicates semi-conservatively.
- 2 samples of bacteria grown. 1 in broth containing light nitrogen and one in broth containing heavy nitrogen.
- As bacteria reproduce, they take up the nitrogen for nucleotides. So nitrogen eventually becomes part of the bacteria’s DNA.
- DNA sample taken from both batches and centrifuged. Heavy nitrogen settled lower in test tube than light nitrogen.
- Heavy nitrogen broth taken out and put in light nitrogen broth.
- DNA settled in one band, so DNA molecules contained heavy and light nitrogen. This proves semi-conservative replication.
What is cystic fibrosis?
Recessive condition
Caused by mutation in gene that codes for the CFTR protein.
CFTR is a channel protein which transports Cl- out of cell and into mucus, making it watery.
Mutant CFTR protein less efficient at transporting Cl- out of cell, so less water moves out into mucus, making it sticky.
This causes problems in the respiratory, digestive and reproductive systems.
How does cystic fibrosis affect the:
Respiratory system?
Digestive system?
Reproductive system?
Respiratory system: cilia unable to move mucus because so sticky and thick. So mucus build up in airways reducing SA for gas exchange. Causing breathing difficulties and increased likelihood of lung infections.
Digestive: tube connecting pancreas to small intestine blocked by mucus. Causing cysts to form which inhibit enzyme production. Mucus lining of small intestine abnormally thick, so inhibits absorption of nutrients.
Reproductive system: tubes connecting testicle to penis blocked with mucus so sperm can’t reach penis. In women, thickened cervical mucus can prevent sperm reaching egg.
Describe identification of carriers and PGD.
Identification of carriers: offered to people with family history of genetic disorders to see if they carry allele for the disorder
Issues: could cause stress or difficulty finding a partner if person finds out they are a carrier.
PGD: involves screening of embryos produced by IVF for genetic disorders. Reduces risk of child inheriting disorders and doesn’t risk abortion as happens before implantation.
Issues: false results and designer babies
Describe amniocentesis and chorionic villus sampling (CVS)
Amniocentesis: testing of DNA in fetal cells in amniotic fluid. Carried out at 15-20 weeks and has 1% risk of miscarriage.
Chorionic villus sampling: sample of cells from chorionic villi taken and DNA analysed. Carried out at 11-14 weeks (earlier than amniocentesis) and has 1-2% risk of miscarriage ( higher than amniocentesis)
