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Biology A level (Edexcel SNAB) > UNIT 2 - Genes and health > Flashcards

UNIT 2 - Genes and health Flashcards

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1
Q

What do gas exchange surfaces in living things tend to have?

A

Large SA:Vol ratio
Thin surface
A steep concentration gradient maintained

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2
Q

State Fick’s Law

A

Rate of diffusion =proportional to= (S.A x conc. gradient) / Thickness of gas exchange surface

It Is porportional, to calculate it, you would need a diffusion coefficient (depends on the substance, temperature and pressure)

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3
Q

Following Fick’s law, which are the three factors that affect the rate of diffusion?

A

Big surface area
Big concentration gradient
Thin exchange surface

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4
Q

How are alveoli adapted to enable a fast diffusion rate?

A

Thin surface - 1 epithelial cell thick

Large surface area - bronchioles divide into lots of alveoli

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5
Q

Which biological molecules are present in the cell membrane?

A

Lipids (phospholipids and cholesterol)
Proteins (inc. enzymes)
Carbohydrates (in the from of glycoproteins and glycolipids)

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6
Q

What are the properties of cell membranes?

A

Flexible
Fluid
Selectively permeable

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7
Q

Which two techniques helped develop models of the cell membrane?

A

Electron microscopy

Use of radioactive isotopes

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8
Q

Describe the fluid mosaic model

A

Has a fluid phospholipid bilayer. Phospholipids heads (polar=hydrophilic) face the outside while the tails (non-polar=hydrophobic) face each other.
Cholesterol and proteins (protein channels and peripheral) float around the mosaic.
Some have carbohydrate groups on the outer surface of the membrane (glycoproteins and glycolipids), which are useful for cell signaling.

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9
Q

What facts and evidence is there for the fluid mosaic model? (6)

A

Phsopholipids have hydrophilic (polar) heads and hydrophobic (non-polar) tails so from bilayer in aqueous environments.
A monolayer of phospholipids is twice as large as the cell S.A.
Microscope images show proteins sticking out.
When lectins (react with carbohydrates) are added, there are found only on the outside.
Some small water soluble substances pass in and out of cells.
Ionic and polar molecules do not pass easily, but lipid-soluble substances do.

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10
Q

What three types of passive transport are there?

A

Diffusion, facilitated diffusion and osmosis.

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11
Q

What is diffusion?

A

Diffusion is the net movement of particles down a concentration gradient (from high conc. to low conc.)

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12
Q

Under what circumstances would diffusion not occur, even though there’s a concentration gradient? (3)

A

The membrane is not permeable enough (molecules don’t fit through pores).
The particle is charged.
The particle isn’t soluble.

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13
Q

What happens, in terms of movement of particles, when the concentration gradient is zero?

A

Particles still move across in all directions but the net movement is zero.

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14
Q

How does facilitated diffusion happen?

A

Big, non-polar molecules or polar molecules can’t pass across the phospholipid bilayer so they move across a channel protein (like a pore) to enter and exit the cell. They can also be aided by a carrier protein for the specific molecule, which changes shape, ‘pushing’ the molecule into/outside the cell.

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15
Q

What is osmosis?

A

Osmosis is the net movement of water molecules down a water potential gradient (from areas of high W.P. to areas of low W.P.) through a partially permeable membrane.

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16
Q

How does active transport work?

A

The specific molecule gets into the carrier protein. The carrier protein the changes shape (using energy from ATP) , therefore pushing the molecule to move against the concentration gradient.

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17
Q

What is the structure of adenosine triphosphate (ATP)?

A

An adenine nitrogenous base bonded to a ribose sugar, which is bonded to a chain of three phosphate groups.

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18
Q

How is energy harvested from ATP?

A

The bond between the second and the third is broken by hydrolysis, so energy is released:
Then energy is required to add the third phosphate to re-build the phosphate bond to adenosine diphosphate to create ATP again.

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19
Q

What happens during endocytosis?

A

A cell or a molecule becomes surrounded by the cell membrane and, due to the fluid nature of the cell membrane, a vesicle is created around it when it enters the cell, without destroying the cell membrane.
E.g. phagocytosis (solids)
e.g. pinocytosis (liquids)

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20
Q

What happens during exocytosis?

A

A particle is inside the cell, engulfed by a vesicle. The vesicle then fuses with the membrane (due to its fluid nature), releasing the contents out of the cell.
e.g. how insulin moves out.

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21
Q

How does temperature affect the permeability of cell membranes?

A

As temperature increases, phospholipids become more fluid, allowing more molecules to leak out of the cell (higher permeability).

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22
Q

Describe an experiment you would carry out in order to investigate how temperature affects membrane permeability. (Core Practical)

A
  1. Cut equal sized pieces of beetroot. (CV)
  2. Rinse under water to remove the betalain released by cutting.
  3. Place pieces in equal volumes of distilled water (CV) at a range of different temperatures (IV) and leave them for equal time (CV).
  4. Carefully remove pieces and shake solution gently.
  5. Asses the amount of pigment lost by using a colorimeter and measuring the % absorbance, which gives a quantitative representation of how permeable the membrane was. (DV)
  6. Plot values on graph to allow the relationship to be seen: temp = x axis; absorbance = y-axis.
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23
Q

Nucleic acids are polynucleotides. What is the general structure of a mononucleotide?

A

Phosphate added by condensation reaction to the C5 in the pentose sugar, which has the C1 bonded to a nitrogenous base, also formed by condensation reaction.

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24
Q

Both DNA and RNA are polynucleotides. How do nucleotides join together to form a polynucleotide?

A

They join by a condensation reaction, which forms a phosphodiester bond between the C3 of the pentose in one nucleotide and the phosphate of ANOTHER nucleotide.

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25
Q

Name the purine bases

A

Adenine and guanine.

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26
Q

Name the pyrimidines bases

A

Cytosine, thymine and uracil.

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27
Q

Which base has RNA got different to DNA

A

Uracil instead of thymine.

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28
Q

How are bases joined together in DNA and how do they affect its structure?

A

Joined together by hydrogen bonds (2 between A and T and 3 between C and G). They form a complementary base pair. (A with T and C with G). These bases form a double-helix structure.

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29
Q

What is meant by the sugar-phosphate backbone?

A

The chain of alternating phosphate and pentose groups. (C5 in pentose is joined to the phosphate by a bond formed during a condensation reaction and the C3 is joined to the phosphate by a phosphodiester bond)

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30
Q

What is a gene?

A

A gene is a section of DNA that codes for a protein.

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31
Q

Which steps are there to protein synthesis.

A
  1. Transcription: The sequence is copied on to a mRNA molecule in the nucleus.
  2. Translation: Ribosomes facilitate the joining of amino acids in the correct sequence.
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32
Q

What is the structure of the mRNA molecule?

A

Single stranded.
Not usually folded.
Carries codons (base triplets).

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33
Q

How does transcription happen?

A
  • In the nucleus, DNA is unwinded( H bonds break) by the helices enzyme into the sense and the antisense strand.
  • Complementary bases in different nucleotides create H-bonds between each other, then causing the phosphodiester bonds to create between the C3 in the pentose and the phosphate group. RNA polymerase is the enzyme that catalyses this process.
  • The result is an mRNA base sequence identical to the sense strand, but with U instead of T.
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34
Q

What is the difference between the pentose sugar in DNA and in RNA?

A 
DNA = deoxyribose
RNA = ribose
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35
Q

What is the structure of the tRNA molecule?

A

Single stranded.
Folded into specific pattern (clover-shaped).
Carries anticodons (complemetary to the ones in mRNA), where it attaches to mRNA.
Has an amino acid binding site.

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36
Q

After transcription, which steps have to happen for a protein to be synthesized?

A
  1. mRNA leaves the nucleus through the nuclear pore.
  2. Amino acid activation - tRNA carries amino acids to the ribosomes.
  3. Translation - mRNA information is translated into a sequence of amino acids.
  4. The polypeptide is then modified to produce a functional protein.
37
Q

What happens during translation?

A

The tRNA molecule, with its corresponding amino acid, binds with the anticodon to the mRNA molecule.
2 tRNA molecules are in the same ribosome at a time, until a peptide bond is created between the amino acids.
The tRNA molecule leaves and the ribosome moves along the mRNA molecule.

38
Q

How many start codons are there?

A

One

39
Q

How many stop codons are there?

A

Three

40
Q

The genetic code is non-overlapping. What does this mean?

A

Every base only forms part of one codon. For example, the sequence UCUUUG consists only of two codons UCU and UUG.

41
Q

The genetic code is a degenerate code. What does this mean?

A

Most amino acids are coded for by more than 1 base triplet (there are 64 possible combinations and only around 20 amino acids). This means that some mutations would have no effects IF the new mutated codon codes for the same amino acid.

42
Q

What is the general structure of amino acids?

A

a central carbon atom joined to

  • a Hydrogen
  • Amino group (NH2)
  • A carboxyl group (COOH)
  • To one of the 20 different R groups.
43
Q

How are peptide bonds created?

A

The OH in the carboxyl group joins with the H in the amino group to create water (condensation reaction). The resultant ‘mix’ between the carboxyl and the amino groups is called the peptide bonds.

44
Q

What is the primary structure of a protein?

A

The sequence of amino acids.

45
Q

How does the secondary structure of a protein form?

A
  1. Amino and carboxylic groups carry small amounts of charge.
  2. The charge is -ve (delta-) on the CO and +ve (delta+) on the NH.
  3. These charges result in hydrogen bonds forming between parts of the chain, which stabilize the structure, forming either an alpha helix or a Beta pleated sheet structure.
46
Q

What two types are there of secondary structure in proteins?

A

Alpha helix and Beta pleated sheet

47
Q

How is the tertiary structure of a protein created?

A

The alpha helix or beta pleated sheets fold further and create a new structure held together by hydrogen bonds, disulfide bonds between R groups and ionic bonds between R groups.

48
Q

How is the quaternary structure of a protein created?

A

Folded polypeptides are joined by H bonds, disulfide bonds between R groups and ionic bonds between R groups.

49
Q

what does the structure of a protein determine?

A

Its function

50
Q

What type of protein is haemoglobin?

A

Globular

51
Q

What type of protein is collagen?

A

Fibrous

52
Q

Describe the structure of hemoglobin

A

Is a globular protein.

With 4 polypeptides (Two alpha chains and Two beta chains), each containing one haem prosthetic group.

53
Q

Describe the structure of collagen

A

Is a fibrous protein.

With 3 polypeptides (Two alpha1 and 1 alpha2). Where alpha(1) and alpha(2) refers to different alpha helix polypeptides.

54
Q

What characteristics does haemogloblin have that allows it to transport oxygen?

A

Globular - so can be soluble
Polypeptide contains haem group (contains iron) - for the oxygen to bind.
4 polypeptides and so 4 haem groups - 4 times more oxygen can bind.

55
Q

Oxygen binds to the haem groups in hemoglobin by cooperative binding. What does this mean?

A

When an oxygen binds to one haem group, it is easier for the next oxygen to bind due to the changes in shapes caused by the changes in the tertiary structure.

56
Q

How does the structure of collagen relate to its function?

A

Fibrous protein - insoluble
The three alpha helices create a triple helix, forming a rope-like strand.
In the three helices, every 3rd amino acid is glycine, whose R group is only -H, which means it can fit into small places inside the triple helix.
On either side are proline and hydroxyproline with big R chains. The chains keep out of each others way to create a strong tissue.
The 3 helices are cross-linked so there are no ‘weak’ points.

57
Q

What type of proteins are enzymes?

A

Globular

58
Q

What are intracellular enzymes?

Give examples

A

Enzymes that work inside the cell e.g. DNA polymerase

59
Q

What are extracellular enzymes?

A

Enzymes that work outside he cell e.g. digestive enzymes

60
Q

Explain the lock and key hypothesis

A
  1. Random movement causes the enzyme and the substrate to collide, and so the substrate enters the active site (complementary in shape).
  2. Enzyme substrate complex forms; shared groups attract, distorting the substrate and aiding in bond breaking or formation.
  3. Products are released from the active site of the enzyme, leaving it unchanged and ready to accept a new molecule.
61
Q

What key piece of information does the induced fit hypothesis state as opposed to the lock and key?

A

The enzyme changes shape to fit the substrate when the substrate is near while in the lock and key model the enzyme and the substrate are always complementary in shape and the enzyme doesn’t change shape.

62
Q

What are enzymes?

A

Biological catalysts.

63
Q

How do enzymes accelerate rates of reaction?

A

They lower the activation energy by providing a lower energy pathway, a more favorable pH in the active site, using charge to put strain on bonds or bring reactants together using charge so bonds are easier to form.

64
Q

Why isn’t heat used to accelerate reactions in living organisms rather than enzymes?

A

It could damage tissue.

65
Q

How does enzyme concentration affect reaction rates?

A

As enzyme concentration increases, the rate of reaction increases since there is more change of successful collisions.
Therefore, more enzyme substrate complexes will be formed per unit time and so more products will be released per unit time.

66
Q

Testing for rate of reactions, how could temperature be controlled as a CV?

A

Use a water bath with temp. as near to the optimum as possible.

67
Q

Testing for rate of reactions, how could pH be controlled as CV?

A

Using a buffer solution, as nearer to the optimum as possible.

68
Q

What happens during the semi-conservative replication of DNA?

A
  1. DNA helices breaks hydrogen bonds between the bases to ‘unzip’ DNA.
  2. DNA nucleotides align with their complementary bases and DNA polymerase creates the phosphodiester bonds that join nucleotides together. DNA ligase joins partly formed strands together.
  3. Two identical daughter strands are created: each has 1 old strand and 1 newly synthesized one.
69
Q

What did the conservative model mean?

A

One completely new double helix is synthesized.

70
Q

What did the dispersive model mean?

A

The new DNA molecule was created of mix of new and old parts.

71
Q

On what did Meselson and Stahl’s experiment consist?

A
  1. E. coli bacteria were cultured in a 15-N containing medium.
  2. Were transferred into a 14-N containing medium.
  3. DNA was extracted after each generation and centrifuged in BaCl solution. The heavier the DNA was, the deeper it was into the test tube.
72
Q

How did Meselson and Stahl’s experiment disproof other theories and proofed theirs?

A
  1. In a conservative model, a super heavy DNA will be expected, with more newly, lighter DNA as generations passed.
  2. In a dispersive model, only one layer of equally dense DNA would be seen, each time getting lighter and lighter.
  3. The results showed an ‘intermediate’ DNA in F1 (half N-14 and half N-15) so the conservative model was disproved. The results also showed two layers in F2, an ‘intermediate’ one and a completely light one, so the dispersive model was disproved. Therefore, it had to be the semi-conservative model.
73
Q

During which three processes can mutations occur?

A

DNA replication
Transcription
Translation

74
Q

How do our bodies decrease the viscosity of our mucus on the apical membrane?

A

Cl- is pumped into the cell across the basal membrane.
Cl- diffuses through the open CFTR channels to outside the apical membrane.
Na+ diffuses down the electrical gradient into the mucus.
Elevated salt concentration in the mucus draws water out of the cell by osmosis.

75
Q

Why do people with cystic fibrosis have sticky mucus?

A

The CFTR channel protein is non-functional.
Therefore, the Na+ channel (ENaC) is always open so NA+ ions move into the cell an to the tissue fluid on the basal membrane.
This causes the Cl- to move down the electrical gradient.
As a result of the water potential gradient, water goes out from the mucus, to the cell and to the tissue fluid.

76
Q

What is meant by monohybrid inheritance?

A

The inheritance of one characteristic

77
Q

Define gene

A

A sequence of bases on a DNA molecule that codes for the sequence of amino acids in a polypeptide chain; it is the molecular unit of heredity.

78
Q

Define allele

A

A version of a gene.

79
Q

Define recessive allele

A

An allele which is not expressed when a dominant allele is present.

80
Q

Define dominant allele

A

An allele which is always expressed.

81
Q

Define incomplete dominance (or co-dominance)

A

Neither allele is dominant over each other and the resultant phenotype is a mix.

82
Q

What symptoms can cystic fibrosis present in gas exchange?

A

Mucus can block bronchioles - less oxygen gets to the alveoli so there’s a smaller concentration gradient.
Mucus reduces the surface area for gas exchange.
The thin layer of mucus can make it difficult for gases like O2 and CO2 to diffuse.

83
Q

What symptoms can cystic fibrosis present in reproduction?

A

In men: vas deferens can get blocked with mucus, so sperm can’t leave the testes.
In women: Mucus blocks the cervix and sperm can’t reach the egg.

84
Q

What symptoms can cystic fibrosis present in digestion?

A

Mucus blocks pancreatic duct, so digestive enzymes can’t reach the duodenum, food isn’t properly digested and absorbed, leads to tiredness and difficulty gaining weight.
Enzymes trapped in the pancreas cause fibrosed cysts.
Damage to insulin producing cells lead to diabetes.

85
Q

What does amniocentesis consist on?

A

A syringe with a needle is inserted into the amniotic sac and fluid is extracted.
Fluid and foetal cells are then separated.
These cells are cultured for 2-3 weeks.
Then the DNA is karyotyped, biochemical tests are also done to both the cells and the fluid.
This is carried when the fetus is 14-16 weeks old.

86
Q

What does chorionic villus sampling consist on?

A

A syringe is inserted in the vagina to take a sample of embryonic tissue from the placenta (from the chorionic villi, more specifically)
The next day, the DNA is karyotyped.
This is carried when the fetus is 8-10 weeks old.

87
Q

What are the factors that one must consider in relation to prenatal screening?

A

Risk of miscarriage during the procedures.
Religious beliefs (right to life)
Potential abortion
The cost of healthcare for a CF person.
Dealing with risks/consequences of false positives and false negatives.

88
Q

In genetic screening of recessive conditions, why are carriers sometimes fall positives?

A

The recessive allele might be detected.

89
Q

What does pre-implantation diagnosis consist on?

A

Embryos created through IVF are tested to see if they carry the faulty allele. Only those that are healthy are implanted into the woman.
However, this is expensive and quite unreliable.

Biology A level (Edexcel SNAB) (5 decks)

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