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A Level Biology (Salters-Nuttfield SNAB) > Topic 2: Genes and health > Flashcards

Topic 2: Genes and health Flashcards

1
Q

What are the properties of a gas exchange surface?

A

The process of gas exchange occurs by diffusion meaning gas exchange is determined by
- surface area to volume ratio (as overall size of the organism increases the surface area becomes smaller
- thickness of surface
- concentration gradient

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2
Q

How are mammals adapted to rapid gas exchange?

A
  • many alveoli provides a large surface area
  • alveoli and capillaries have cell walls that are only 1 cell thick providing a short diffusion distance.
  • extensive capillary network maintain a high concentration gradient.
  • loads of capillaries also creat a large surface area.
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3
Q

Ficks law

A

Rate of diffusion = surface area x concentration gradient / thickness of surface

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4
Q

Structure of a cell membrane

A

There are four main components of a cell membrane
Phospholipid bilayer > this contains phospholipids which have a hydrophilic (polar) head which point outwards and a hydrophobic tail (non-polar) that face inwards.
Cholesterol > regulates the membrane fluidity, allowing the membrane to maintain structure as well as being flexible and able to change shapes.
Proteins > there are two types intrinsic proteins which are found in the outer layer and extrinsic which extend through the membrane. There job is to transport materials in and out of the cell and communicate with other cells.
Glycolipids > lipids with carbon hydrate attached, aid in cell to cell communication (recognition) and can act as cell markers. They can also bind with substances on the cell surface.
Glycoproteins > proteins with carbohydrates attached again aid in cell to cell communication, cell markers and can bind with substances at the cell surface (hormones).

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5
Q

Why is the cell membrane described as as fluid mosaic model?

A

The scattered pattern produced by the components whiting the phospholipid bilayer looks like a mosaic. The movement of the components around the bilayer makes it fluid.

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6
Q

Is the cell membrane permeable?

A

The membrane is partially permeable. Small, non-polar molecules can pass through gaps between the phospholipids whereas large polar molecules must pass through the channel and carrier proteins.

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7
Q

What is osmosis?

A

The movement of water molecule from an area of high water concentration to an area of low water concentration (down the concentration gradient) through a partially permeable membrane.

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8
Q

Passive diffusion

A

The movement of particles from an area of high concentration to an area of low concentration. (Down the concentration gradient)
e.g. The movement of small, non polar molecules through the phospholipid bilayer form

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9
Q

Facilitated diffusion

A

The movement of large, polar molecules through carrier through carrier and channel proteins form an area of high concentration to an area of low concentration.

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10
Q

Channel proteins

A

Proteins that extent though the membrane which allow charge substances to diffuse through the cell membrane. They can close and open allowing them to control the exchange of any ions.

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11
Q

Carrier proteins

A

Channel proteins change shape to allow molecules of pass through. Molecules bind to the carrier protein which then changes shape opening on the other side of the membrane. Happens down a concentration gradient.

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12
Q

What is active transport?

A

The movement if molecules through a cell membrane from a regions of lower concentration to a region of higher concentration, against the concentration gradient. It requires carrier proteins and ATP energy.

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13
Q

What is exocytosis?

A

The movement of large polar molecules contained within vesicles which fuse with the cell membrane and release their contents out of the cell.
Require a source of energy.

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14
Q

What is endocytosis?

A

When a molecule is two large to travel through proteins the cell can surround the substance with a section of the cell surface membrane. It then engulfs the substance and seals it of inside the cell creating a temporary vesicles.
Requires a source of energy

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15
Q

What’s the structure of a mononucleotide in DNA?

A

DNA nucleotide ps are made up of a deoxyribose sugar, a phosphate group and one of four nitrogenous bases (adenine, cytosine, guanine or thymine).

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16
Q

What’s the structure of a RNA mononucleotide?

A

The components of a RNA nucleotide are a ribose sugar, a phosphate group and one of the four bases.

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17
Q

How do mononucleotides from polynucleotides?

A

Separate nucleotides are joined by a condensation reaction forming a phosphodiester bond between the phosphate group of one nucleotide and the pentose sugar of the next. Forming polynucleotides such as DNA and RNA.

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18
Q

How is the sugar-phosphate backbone created?

A

Made up of a chain of alternating nucleotides held together by phosphodiester bonds making a sugar-phosphate backbone. Through condensation reaction.

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19
Q

What is the structure of a DNA molecule?

A

A double helix molecule comprised of two strands - which run in opposite directions) of polynucleotides which are he,d together by hydrogen bonds between complementary base pairs (G and C, A and T). Backbone comprised of deoxyribose sugar and phosphate group.

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20
Q

What so the structure of RNA?

A

This is a single strand of polynucleotides in which T bases are replaced by U. The backbone is comprised of ribose sugar and a phosphate group.

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21
Q

What is the process of transcription?

A

Transcriptions if the first step of protein synthesis and occurs in the nucleus
1. DNA helicase unzips the two stands of the double helix, by braking the hydrogen bind between the strands, exposing the template (antisense) strand.
2. Free-floating RNA nucleotides bind to the template strand forming a complementary mRNA strand. (T bases replaced by U bases)
3. Hydrogens bonds form between complementary base pairings. (A and U and G and C)
4. RNA polymerase cause phosphodiester binds to form between the adjacent nucleotides in a condensation reaction.
5.. When the mRNA molecule is complete, the hydrogen bonds are broken and the mRNA strand leaves through the nuclear pores in the nuclear envelope.

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22
Q

The process of translation?

A

The second part of protein synthesis which occurs in the cytoplasm of the cell.
1. After leaving the nuclear, the mRNA molecule binds to a ribosome.
2. Free tRNA molecules bind wiht their specific amino acid in the cytoplasm and brings them to the mRNA molecule on the ribosome.
3. The triplet anticodons on each tRN A pairs with a complementary triplet (a Condon) on the mRNA molecule.
4. The amino acid form peptide binds with adjacent amino acid in a condensation reaction growing the polypeptide chain and each tRNA detaches.
5. Translation stops when a STOP condon is reached.

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23
Q

What is the nature of the the genetic code?

A

The genetic code is
Universal > the same codons code for the same amino acids in all organisms.
Degenerate > some codons code for the same amino acid.
Non overlapping > each base is only read one, each codon is transcribed separately.

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24
Q

Definition of a gene

A

A a sequence of bases on a DNA molecule that codes for a sequence of amino acids in a polypeptide chains.

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25
Q

Definition of a genome

A

The collection of all the genes in an organism.

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26
Q

What is the basic structure of an amino acid?

A

Amino acids are the monomers of a polypeptides and has a general structure of
H H O
\ I //
N - C - C
/ I \
H R OH
- amine group (NH2)
- carboxylic acid (COOH)
- R group (where each amino acid differs)

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27
Q

How do amino acids join to make a polypeptide chain?

A

Amino acids join together by a condensation reaction forming polypeptide bonds. It can be broken by a hydrolysis reaction (gaining water).

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28
Q

What is the primary structure of a polypeptide chain?

A

The sequence of amino acids in a polypeptide chain. It determines the its 3D shape and therefore its properties.

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29
Q

What is the secondary structure of a polypeptide chain?

A

The 2D arrangement of amino acids in a polypeptide chain. It controlled by the formation of hydrogen binds between partially charged R groups. It can either be an alpha-helix or beta-pleated sheet.

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30
Q

What is a tertiary structure of a polypeptide chain?

A

The 3D folding of the secondary structure of polypeptides and is controlled by chemical bonding - hydrogen, disulphide, ionic and weak hydrophobic interactions.

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31
Q

What is the quaternary of a polypeptide chain?

A

When more than one polypeptide chain work together as a functional molecule.

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32
Q

What is the structure of a globular protein?

A

A polypeptide chain held in a 3D spherical structure by bonds (disulphide, ionic and hydrogen). There non polar hydrophobic R groups are orientated towards the centre of the proteins and the polar hydrophilic R grounds oriented themselves on the outside of the protein creating the spherical shape.
E.g. Haemoglobin

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33
Q

How does the structure of a globular protein relate to its structure?

A

The orientation of the R groups enable globular proteins to be soluble in water making it easily transported around an organism and be involved in metabolic reactions.

34
Q

What is the structure of a fibrous protein?

A

Long strands of polypeptide chains held together by hydrogens (have no tertiary structure)
E.g. collagen

35
Q

How are the structure of fibrous proteins related to their function?

A

The additions of the hydrogen bonds (cross linkages) proved the protein with extra tensile strength making them ideal for structural purposes (strength and support).
They are also insoluble.

36
Q

What is haemoglobin?

A

It’s a 4 beta-polypeptide with the additional haem group allowing it to bind to oxygen and carry it to the blood.

37
Q

What is collagen?

A

A triple alpha-helix polypeptide with high amounts of tensile strength due to its hydrogen and covalent bonding. It forms the structure of bones, cartilage and tendons.

38
Q

What is an enzyme?

A

An enzyme is a biological catalyst meaning they speed up the rate if chemical reactions in the body by lowering the activation energy. They aren’t used up or changed in the reaction.

39
Q

How does the structure of an enzyme relate to their function?

A

Enzymes are protein with a complex tertiary and quaternary structure. This means there active sites can distort to fit a substrate forming a enzyme-substrate complex and lowering the activation energy.

40
Q

What’s an intracellular enzyme?

A

Enzymes that are produced and function inside of the cell.

41
Q

What are extracellular enzymes?

A

Enzymes that are secreted by the cells and catalyse reactions outside the cell.

42
Q

What is the model of enzyme action?

A

Enzymes are globular proteins meaning the shape of its active site is largely determined by the tertiary structure that makes up the enzyme. Each enzyme has a unique active site where specific enzymes can bind forming a enzyme-substrate complex.
For it to bin pd it must happen as the correct orientation and speed.

43
Q

What is meant by enzyme specificity?

A

The result of the complementary nature between the shape of the active site in the enzyme and its substrate.
- proteins are formed from chains of amino acids held together by peptide bind in a condensation reaction.
- the order of amino acids determine the shape of an enzyme
- if the order is altered, the 3D shape will be different due to different binds those changing the shape of the active site and substrate will no longer fit.

44
Q

What factor effect enzymes activity?

A
  • enzyme concentration
  • substrate concentration
  • temperature
  • pH
45
Q

What is the process of DNA replication?

A

DNA replication is semi-conservative and occurs in the nucleus.
1. DNA helicase separates the double-helix by breaking the hydrogen bonds between the strands.
2. Free floating DNA nucleotides bind to their complementary bases joined by hydrogen bonds.
3. DNA polymerase causes the phosphodiester bonds to forms between adjacent nucleotides.
4. This results in a new DNA double helix consisting of one new and one old strand identical to the original.

46
Q

What was the purpose of Meselson and Stahl experiment.?

A

Melselson and Stahl conducted there experiment to conclude whether DNA replication was conservative, semi-conservative or fragmentary.

47
Q

What was the steps of Meselson and Stahl reaction?

A
  1. Bacteria was grown in a broth containing heavy Nitrogen 15. After some time the DNA would contain only heavy 15N. (nitrogen is found in the bases)
  2. It was then spun in a centrifuge which showed the DNA settled near the bottom.
  3. The bacteria was then allowed to replicate in 14N (light).
    4.After the first replication, it was extracted and spun again in the centrifuge. A medium band indicating that the DNA was made up of one heavy and one light band. disproving conservative replication.
  4. It was then allowed to replicate again, producing a light band as well as a medium band (disproving fragmentation) confirming semi-conservative.
48
Q

Why was each of the DNA replication theories proved wrong?

A

Conservative > the original template molecule would stay the same and new DNA molecules would only contain lighter nitrogen. So there would be one heavy band and one light band.
Fragmentation > would only produce one band on DNA (medium p) containing parts of both heavy and light DNA.

49
Q

What is a gene mutation?

A

A random change in the sequence of base pairs in a DNA molecule which may result in an alternative polypeptide.

50
Q

Insertion mutation

A

When a nucleotide is randomly inserted into the DNA sequence. This changes the amino acid that would be coded for as well as having a knock on effect of the rest of the triple condons ‘frame shift mutation) dramatically changing the polypeptide chain and therefor the protein shape.

51
Q

Deletion of nucleotides

A

A mutation that occurs when a nucleotide is randomly deleted from the DNA sequence. This again changes the triplet as well as creating a ‘frameshift’ . Changing the polypeptide chain resulting in it not being able to perform its function.

52
Q

Substitution mutation

A

When a base in the DNA sequence is randomly swapped for a different base. It will only change one triplet so can be silent (doesn’t alter polypeptide), missense (changes one amino acid) or nonsense (premature stop condon)

53
Q

How does a gene mutation cause cystic fibrosis?

A

A mutation (substitution-nonsense) in the CFTR gene leads to a production of non-functional chloride channels.
1. This reduces the movement of chlorine in and out of the cell
2. Resulting a fewer sodium ions can leave the cell.
3. This lack of concentration gradient reduces the movement of water by osmosis into the mucus outside the cell.
4. Cause the mucus to become thick and sticky.

54
Q

What is cystic fibrosis?

A

A genetic disorder of cell membranes caused by the inheritance of a recessive allele (CFTR).

55
Q

Effect of cystic fibrosis on the respiratory system?

A

Mucus is important to trap pathogens for them to be removed by cilia hairs.
The thick sticky mucus means
- the cilia are unable to move as the mucus is so thick meaning pathogens stay in the respiratory tract creating high risk of infection.
- mucus build up in the lungs can block air ways limiting gas exchange.
- mucus decrease the amount of functioning alveoli reducing lung surface area and efficient of gas exchange.

56
Q

The effect of cystic fibrosis on the digestive system?

A
  • mucus blocks the pancreatic duct meaning digestive enzymes are trapped reducing nutrients absorption.
  • thickness lining of the intestine inhibiting the absorption of nutrients in the small intestine.
  • mucus traps digestive enzymes which can damage pancreatic cells that produce insulin. May cause her formation of cysts and diabetes.
57
Q

What effect does cystic fibrosis have on the reproductive system?

A
  • cervical mucus is thicken preventing sperm reaching the ovaries and egg
  • mucus can mock the tubes of the testers preventing sperm reaching the penis.
58
Q

What is the definition of an allele?

A

Different copies of the same gene found at the same locus.

59
Q

What is the definition of a genotype?

A

The combination of alleles of a gene posed by an individual.

60
Q

What is the definition of phenotype?

A

The observable characteristics expressed by an organism. Controlled by the interactions of the genotypes and the environment.

61
Q

What is the definition of a dominant allele?

A

An allele that always expresses its phenotype if present in the genotypes (no matter what other allele is present)

62
Q

What is the definition of a recessive allele?

A

An allele that only expresses its phenotype if the other allele is also recessive.

63
Q

What is the meaning of incomplete dominance?

A

This occurs when the trait from a dominant allele is not completely expressed over the trait produced by the recessive allele.

64
Q

What is the definition of homozygote?

A

A a genotype that contains two copies of the same allele. Either HH or hh

65
Q

What is the definition Of a heterozygote?

A

A genotype that contains both types (recessive and dominant) of allele Hh.

66
Q

What is a pedigree diagram?

A

Pedigree diagrams can be used to trace the pattern of inheritance of a specific trait.
Square shape represents male
Circular represents females

67
Q

What information does a pedigree diagram show?

A
  • whether a trait is caused by a recessive or dominate allele.
  • whether a trait is more likely to be inherited by a male or female.
  • the probability that an individual in the family will inherit a trait.
68
Q

What is monohybrid inheritance?

A

This is when one gene at one loci is responsible for the inheritance of a single characteristic or phenotype.

69
Q

How can monohybrid inheritance be presented?

A

Using a monohybrid cross/ Punnett squares.
I T I t
— ———————
T I TT I Tt
- I —— I ———
t I Tt I tt

70
Q

What is the purpose of genetic screening?

A

The purpose of genetic screening is to determine if the DNA of an individual foetus/fertilised embryo contains any genetic disorders or if they carry any genetic disorders.

71
Q

What are the different types of genetic screening?

A
  • identification of carriers
  • pre-implantation genetic diagnosis (PGD)
  • prenatal tasting (amniocentesis and chronic villus sampling)
72
Q

What is identification of carriers?

A

Carrier testing is offered to individuals with a history of genetic disorders in their family. It shows whether they carry an allele for particular disorders and can therefor determine the probability of future children inheriting the condition.

73
Q

What is the process of preimplantation genetic diagnosis and potential benefits and negatives?

A

This is where an embryo created via IVF is tested for genetic disorders prior to be implanted.
+ carries no risk of miscarriage
- presents opportunities for ‘designer babies’ and may result is the discard of unwanted embryos.

74
Q

What is prenatal testing?

A

Offered to pregnant women with a history or genetic diseases. The DNA can be obtained via chronic villus sampling and amniocentesis .

75
Q

What is the process of chronic villus sampling including benefits and negatives)

A

This is when a sample of embryonic tissue is taken from the placenta using a needle.
It is perfumed quite early on in the pregnancy (8-12 weeks) .
+ can detect genetic disorder early on reducing possible trauma for the parents and allows parents to make informed decisions.
- can cause a higher risk of miscarriage and cannot detect genetic disorder from the X chromosome.

76
Q

What is the process of amniocentesis and benefits and negatives?

A

This is where a sample of amniotic fluid is taken using a needle via the abdomen and then tested. Performed at 15-20 weeks pregnant.
+ carries a lower risk of miscarriage
- later on in the pregnancy (more trauma on parents)

77
Q

What are the benefits of genetic testing?

A
  • test allow parents to make informed decisions about their future child
  • gives them time to prepare for the future care of their child (medical treatment)
78
Q

What are the ethical issues associated with genetic screening?

A
  • increases chance of miscarriage (may be unethical to cause the death of a foetus)
  • outcome of testing may lead to an abortion (unethical)
  • risk of a false positive (unethical to abort a healthy foetus)
  • may lead to ‘designer babies) where the foetus characteristics can be chosen.
  • extra financial stain, emotional and mental issues associate with raising a child with a genetic disorder.
79
Q

Cora particle - effect of enzyme concentration on into all rate or reactions. Variables

A

Control >
- type of enzyme
- type of substrate
- volume of substrate
- temperature
Independent > enzyme contraction, substrate concentration or temperature
Dependent > volume of oxygen gas produced every 10 seconds

80
Q

Method for effect of enzyme concentration on initial rate of reaction?

A
  1. Make 5 serial dilutions of enzyme
  2. Add 1cm3 catalase, 5cm3 of hydrogen peroxide and 1cm3 of buffer to a conical flask
  3. Apply bung and collect gas in a burette submerged in a water bath for 1 minute recording gas produced every 10s.
  4. Repeat and plot results on a graph and calculate initial rate of reaction for each (tangent).

A Level Biology (Salters-Nuttfield SNAB) (8 decks)

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