2) Genes and Health

Question 1

what happens to the surface area as the size of the organism increases?

Answer 1

the surface area becomes smaller in comparison to the organism’s volume so the SA:V decreases

Question 2

how is a conct gradient maintained in the lungs?

Answer 2

1)alveoli have a good blood supply 2)ventilation system in mammals constant inhalation and exhalation

Question 3

what is Fick’s law?

Answer 3

It states that the rate of diffusion across an exchange surfaces (e.g. membrane, epithelium) is = (surface area x difference in concentration gradient) / thickness of surface. The larger the area and difference in concentration is and the thinner the surface is, the quicker rate the diffusion has.

Question 4

how are alveoli adapted for their function?

Answer 4

1) alveolar wall consists of a single layer of flattened or squamous epithelium which is very thin and permeable for the easy diffusion of gases
2)the alveoli are surrounded by elastic fibres, allowing them to stretch during inhalation 3)surrounded by an extensive capillary network
4)a layer of moisture lines the alveoli facilitating the diffusion of gases so o2 and co2 can dissolve in the layer of moisture so exchange occurs in solution rather with the air

Question 5

what are the role of cell membranes?

Answer 5

1)separating external and internal environments 2)intracellular membranes form compartments 3)control the exchange of substances 4)acting an interface for communication

Question 6

describe how phospholipids are arranged in a plasma membrane?

Answer 6

Phospholipids are arranged in a bilayer (a double layer). They have hydrophobic tailss (made of fatty acids) and hydrophilic heads (made of a phosphate group).

The hydrophilic heads are to the outside and the tails to the inside.

Question 7

describe the structure of cell membranes

Answer 7

1) Intrinsic and extrinsic proteins are involved with cell transport and communication 2) Cholesterol can be found between phospholipids, where it regulates membrane fluidity 3) Glycolipids and glycoproteins are present on the surface of the cell, where they aid cell-to-cell communication

Question 8

which type of molecules can pass through the membrane?

Answer 8

small, non-polar molecules can pass through the gaps between phospholipids

Question 9

which type of molecules cannot pass through the membrane?

Answer 9

laege, polar molecules must pass through specialised membrane proteins called channel proteins and carrier proteins

Question 10

what are the role of channel proteins?

Answer 10

they allow charged substances e.g. ions to diffuse through the cell membrane (facilitated diffusion)

Question 11

what are the role of carrier proteins ?

Answer 11

carrier proteins change shape to transport polar molecules or ions across the membrane

Question 12

why does active transport require energy and where does it get the energy from?

Answer 12

moves substances against their conct gradient - active process so needs ATP from respiration

Question 13

do endocytosis and exocytosis require energy?

Answer 13

yes they are active processes

Question 14

why can water molecules still pass through the bilayer even though they are polar?

Answer 14

because of their small size

Question 15

what is the difference between DNA and RNA?

Answer 15

1)RNA contains nitrogenous base Uracil instead of Thymine
2)RNA contain the pentose sugar ribose instead of deoxyribose
3)RNA is single stranded instead of double stranded (made of one polynucleotide strand) - shorter too

Question 16

what are the similarities of DNA and RNA?

Answer 16

1)both made of many nucleotides linked together in a chain
2)both contain the nitrogenous bases adenine, guanine and cytosine

Question 17

define gene

Answer 17

a sequence of nucleotide bases in a DNA molecule that codes for the production of a specific sequence of amino acids that in turn make up a specific polypeptide (protein)

Question 18

outline the process of transcription

Answer 18

1)occurs in the nucleus where the DNA unwinds using DNA helicase to break the hydrogen bonds between the complimentary base pairs 2) Free activated RNA nucleotides attach onto the exposed template to the complementary bases via hydrogen bonds 3)the sugar-phosphate groups of these RNA nucleotides are then bonded together in a reaction catalysed by the enzyme RNA polymerase to form the sugar-phosphate backbone of the mRNA molecule
4)when the gene is transcribed and the mRNA molecule is complete the hydrogen bonds between the mRNA and DNA strand break and the double stranded DNA molecule reforms 5)the mRNA molecule leaves the nucleus via a pore in the nuclear envelope

Question 19

outline the process of translation

Answer 19

1)in the cytoplasm the mRNA attaches to a ribosome
2) each tRNA has the complementary anticodon to the codon on the mRNA
3)the first tRNA forms hydrogen bonds with the start codon on the mRNA 4) The second tRNA bonds with the next codon on the mRNA
5) a peptide bond forms via a condensation reaction between the two amino acids
6)the process continues until a ‘stop’codon on the mRNA molecule is reaches and the amino acid chain forms the final polypeptide

Question 20

describe the nature of the genetic code

Answer 20

1) Degenerate - multiple codons can code for the same amino acids e.g. CUA and UUG both code for Leu
2) non-overlapping - each base is only read once and adjacent codons do not overlap
3) universal - almost every organism uses the same code , same triplet codes code for the same amino acids in all living things

Question 21

describe the structure of an amino acid

Answer 21

Question 22

what is the primary structure of a protein

Answer 22

the specific sequence of amino acids bonded by covalent peptide bonds is the primary structure of the protein

Question 23

what is the secondary structure of a protein

Answer 23

the hydrogen bonds formed (between amino and carboxyl groups) that result in a-helix or B-pleated sheets

Question 24

what is the tertiary structure of a protein

Answer 24

the interactions between the R groups that result in the overall 3D shape of the protein

Question 25

compare globular and fibrous proteins

Answer 25

1) globular compact whereas fibrous proteins have little or no tertiary structure
2) globular and spherical in shape whereas fibrous proteins are long strands of pp chains that have cross-linkages due to hydrogen bonds
3) globular soluble in water whereas fibrous proteins are insoluble in water

Question 26

when does DNA replication take place?

Answer 26

during interphase the DNA is doubled

Question 27

what happens during DNA replication

Answer 27

1)Each of the single polynucleotide strands acts as a template for the formation of a new strand made from free nucleotides that are attracted to the exposed DNA bases by base pairing
2) The new nucleotides are then joined together by the enzyme DNA polymerase
3)The original strand and the base strand join together by hydrogen bonding between the base pairs to form the new DNA molecule
4) A second enzyme known as DNA ligase is needed to join these lagging strand segments together to form a continuous complementary DNA strand

Question 28

Describe Meselson and Stahl’s experiment

Answer 28

One sample of bacteria was grown in a nutrient broth containing light nitrogen (N14) and one was grown in a broth with heavy nitrogen (N15). The bacteria took up the nitrogen to make new nucleotides so it was incorporated into their DNA. A sample of each was taken and centrifuged, and the DNA grown in the heavy nitrogen settled lower in the tube than the light nitrogen did. The DNA grown in the heavy nitrogen broth was taken and replicated again but this time in the light nitrogen. When centrifuged, it settled at a point in between where the heavy and light nitrogen did, showing that it kept a strand of the old DNA and created a new strand with the light nitrogen. Therefore, the DNA replicated semi-conservatively.

Question 29

what is a mutation ?

Answer 29

a change in the sequence of base pairs in a DNA molecule that may result in an altered polypeptide

Question 30

what causes CF?

Answer 30

a mutation in the CFTR gene (recessive allele) leads to the production of non-functional Cl- channels required for the secretion of mucus, sweat, and digestive juices

Question 31

what problems does CF cause in the respiratory system?

Answer 31

1)the cilia are unable to move as the mucus is so thick and sticky, so microorganisms are not efficiently removed from the lungs and cause lung infections more frequently
2)Mucus builds up in the lungs and can block airways which limits gas exchange, the SA for gas exchange is reduced (physiotherapy to help loosen mucus)

Question 32

what problems does CF cause in the digestive system?

Answer 32

1)the tube to the pancreas becomes blocked by thick mucus preventing digestive enzymes from entering the small intestine - so digestion of some food may be reduced and therefore key nutrients may not be made available for absorption
2) the mucus can cause cysts to grow in the pancreas which inhibit the production of enzymes, further reducing digestion of key nutrients
3)the lining of the intestines is also coated in thick mucus, inhibiting the absorption of nutrients into the blood

Question 33

how does CF affect the reproductive system?

Answer 33

1)In men the tube of the testes can become blocked, preventing sperm from reaching the penis
2)In women thickened cervical mucus can prevent sperm from reaching the oviduct to fertilise an egg

Question 34

what is a chromosome?

Answer 34

a long DNA molecule which contains genes that code for several different proteins

Question 35

what is a homologous pair of chromosomes?

Answer 35

a pair of chromosomes that match in size and shape, and that contain the same genes at the same loci (may not contain the same alleles for each gene)

Question 36

what is a genotype?

Answer 36

the alleles of a gene possessed by that individual

Question 37

what is a phenotype?

Answer 37

the observable characteristics of an organism

Question 38

what is a dominant allele?

Answer 38

always expressed in the phenotype regardless of which allele is present

Question 39

What is a recessive allele?

Answer 39

only expressed in the phenotype no matter which other allele is present

Question 40

what is incomplete dominance?

Answer 40

When the trait from a dominant allele is not completely expressed over the trait produced by the recessive allele. Both alleles influence the phenotype in a heterozygous individual, giving rise to a third phenotype

Question 41

what is chi-squared?

Answer 41

1) completed when data is categorical
2) degrees of freedom (subtract 1 from the classes of data)
3) look at the chi-squared table to work out the critical value
4) if the chi-squared value is larger than the critical value, there is a less than 5% chance that the difference is due to chance. So the null hypothesis can be rejected and the difference is significant
5) if the chi-squared value is smaller than the critical value then there is a more than 5% chance that the difference is due to chance. So the null hypothesis can accepted and the difference is not significant.

Question 42

what is PGD?

Answer 42

analysis of an embryo prior to implanting it into the uterus