Genes & Health

Question 1

Describe the primary structure of a protein.

Answer 1

The specific sequence of amino acids in a polypeptide chain joined together by peptide bonds in condensation reactions.

Question 2

Describe the secondary structure of a protein.

Answer 2

polypeptide chain coils into alpha helixes caused by hydrogen bonds or folds into beta pleated sheets.

Question 3

Describe the tertiary structure of a protein.

Answer 3

Further folding of the secondary structure into a specific 3D shape. Held together by bonds between amino acid R groups.

Disulphide, ionic or hydrogen bonds formed.

Question 4

Describe the quaternary structure of a protein.

Answer 4

3D arrangement involving more than one polypeptide chain.

Question 5

Describe globular and fibrous proteins.

Answer 5

Globular proteins are compact and spherical. They are soluble. e.g. haemoglobin

Fibrous proteins are long chains that are strong and cross-linked. They are insoluble.
e.g. collagen

Question 6

Where are the polar R groups found in a protein and why?

Answer 6

Found on the outside surface of the protein because they are hydrophilic therefore are attracted to other polar molecules.

Question 7

Where are the non-polar R groups found in a protein and why?

Answer 7

Found on the inside of the protein because they are hydrophobic therefore repel other polar molecules.

Question 8

Describe a conjugated protein.

Answer 8

Proteins with another chemical (prosthetic/ non-protein) group associated with their polypeptide chain/s.
e.g. glycoproteins and lipoprotein.

Question 9

Name the 7 components of the Fluid Mosaic Model.

Answer 9

Proteins, glycolipids, glycoproteins, phospholipids, carrier channel (transmembrane) proteins, cholesterol, carbohydrates

Question 10

Give two properties of cell membranes.

Answer 10

Fluid and therefore flexible.
Selectively/ partially permeable.

Question 11

Describe the phospholipid bilayer.

Answer 11

Phosphate heads are polar and hydrophilic. Fatty acid tails are non-polar and hydrophobic.

Question 12

Describe the structure of a phospholipid.

Answer 12

Phosphate head group and two fatty acids joined by a glycerol backbone by ester bonds.

Question 13

Name the three passive transport processes.

Answer 13

Diffusion, Osmosis, Facilitated Diffusion

Question 14

Name the three active transport processes.

Answer 14

Active transport, Exocytosis, Endocytosis

Question 15

Define diffusion.

Answer 15

Net movement from an area of high concentration to an area of low concentration, down a concentration gradient.

Question 16

Define facilitated diffusion.

Answer 16

Movement from an area of high concentration to an area of low concentration, through carrier or channel proteins.

Question 17

Define osmosis.

Answer 17

Net movement of water molecules from an area of low solute concentration to an area of high solute concentration through a partially permeable membrane. Continues until isotonic.

Question 18

Define active transport.

Answer 18

Movement from an area of low concentration to an area of high concentration through a carrier protein using ATP energy.

Question 19

Define exocytosis.

Answer 19

Bulk transport out of a cell. A membrane bound vesicle, with the substance inside, fuses with the cell membrane and the vesicle membrane becomes part of the cell membrane, releasing the substance.

Question 20

Define endocytosis.

Answer 20

Bulk transport into a cell. The cell membrane invaginates (bulges inwards) to form a vesicle which pinches off, enclosing the substance.

Question 21

Name the two stages of protein synthesis.

Answer 21

Transcription and Translation.

Question 22

Describe DNA.

Answer 22

Made up of a phosphate, deoxyribose sugar and a nitrogenous base of adenine, thymine, guanine or cytosine. This is a nucleotide, with phosphodiester bonds, formed by a condensation reaction.

Question 23

Describe RNA.

Answer 23

Made up of a phosphate, a ribose sugar and a nitrogenous base of adenine, uracil, guanine and cytosine.

Question 24

Describe transcription.

Answer 24

Enzyme DNA helicase unzips the double helix, exposing the two strands by breaking the hydrogen bonds between the bases. Anti-sense strand of DNA is used as template. Enzyme RNA polymerase base pairs free complementary nucleotides with phosphodiester bonds, forming the coding strand, which produces a single strand of RNA (mRNA).

Question 25

Describe translation.

Answer 25

mRNA leaves the nucleus and attaches to the ribosomes in the cytoplasm. Triplets of bases form codons which are matched with complementary anticodons on tRNA. Amino acids attached to tRNA forms peptide bonds and primary structure.
Translation is caused by a start and a stop codon.
The code is non overlapping and degenerate.

Question 26

What are the different types of mutations?

Answer 26

Substitution and insertion/ addition, deletion causes frame shift.

Question 27

Explain how mutation changes function of protein e.g. enzyme.

Answer 27

• Mutation results in a change in base sequence of DNA.
• So there is a change in primary structure.
• So change in position of the ionic bonds so protein is folded differently.
• Therefore this causes a change in enzyme shape/ active site.
• So no enzyme-substrate complexes can be formed.

Question 28

Describe what happens when there is extra water in the mucus.

Answer 28

Sodium is transported across the basal membrane and diffuses through sodium channels. Chlorine diffuses down an electrical gradient. Water is drawn out of cells due to the high salt concentration and then drawn out of the mucus.

Question 29

Describe what happens when there is too little water in the mucus.

Answer 29

Chlorine is transported across the basal membrane and diffuses through an open CFTR channel. Sodium diffuses down an electrical gradient. Water is drawn out of the cell and into the mucus.

Question 30

Describe what happens in cystic fibrosis sufferers.

Answer 30

CFTR channel is absent or dysfunctional. Sodium channel is permanently open. Water is constantly being removed from mucus. Mucus becomes thicker, stickier and viscous.

Question 31

Describe the effect of cystic fibrosis on the digestive system.

Answer 31

Pancreatic duct blocked with mucus, prevents release of digestive enzymes, food is not digested properly, resulting in malabsorption syndrome.

Question 32

Describe the effect of cystic fibrosis on the reproductive system.

Answer 32

Females are less likely to become pregnant due to a mucus plug in the cervix caused by viscous mucus.

Males may have a mucus plug in the vas deferens or may lack the vas deferent due to the viscous mucus which blocks the sperm duct and prevents sperm from being released.

Question 33

Describe how the lungs are adapted for rapid gas exchange.

Answer 33

-many alveoli provide a large surface area to volume ratio for gas exchange.
-alveoli/ capillary walls are one cell thick enabling a short diffusion pathway.
-ventilation of the alveoli maintains a steep concentration gradient.
-extensive capillary network around alveoli provides large surface area for gas exchange.

Question 34

Describe the nature of the genetic code.

Answer 34

-triplet code
-non-overlapping
-degnerate
-universal

Question 35

Describe the structure of a mononucleotide.

Answer 35

The pentose sugar in a DNA mono nucleotide is deoxyribose. The one organic base in a DNA mononuclotide could be adenine, cytosine, guanine, thymine. Nitrogen is found in the base of a mononucleotide.

Question 36

Describe structure of DNA.

Answer 36

DNA mononucleotides are joined together by phosphodiester bonds in condensation reactions to form two DNA strands. The two stands twist around each other forming a double helix and are joined by hydrogen bond between bases, which hold the two strands together.

Question 37

Describe DNA replication.

Answer 37

Enzyme DNA helicase breaks the hydrogen bonds between two DNA strands. Both DNA strands act as templates. Free mono nucleotides line up along both DNA strands and complementary base paring occurs. Hydrogen bonds form between bases to join the two DNA strands. Enzyme DNA polymerase joins adjacent mononucleotides with phosphodiester bonds in condensation reactions. Enzyme ligase follows and glues fragments together. (Semi-conservative replication).

Question 38

Define gene.

Answer 38

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

Question 39

Define allele.

Answer 39

Alternative forms of a gene found at the same locus on a chromosome.

Question 40

Define genotype.

Answer 40

The alleles in an organism, for a particular gene.

Question 41

Define phenotype.

Answer 41

The observable characteristic, due to the expression of a genotype/alleles, which may be affected by the environment.

Question 42

Define recessive allele.

Answer 42

Both alleles need to be present in order for the recessive phenotype to be observed (only expressed if the dominant allele is not present).

Question 43

Define dominant allele.

Answer 43

Only one allele needs to be present for the dominant phenotype to be observed.

Question 44

Define incomplete dominance.

Answer 44

When there are two different alleles in the genotypes and both alleles are expressed in the phenotype of the organism - both alleles have an equal weighting in the expression.

Question 45

Define homozygous.

Answer 45

A genotype where both alleles present at a gene locus are the same.

Question 46

Define heterozygous.

Answer 46

A genotype where both alleles present at a gene locus are different.

Question 47

Define homologous chromosomes.

Answer 47

A pair of chromosomes, similar in length, with the centimetre and genes in the same position.

Question 48

Define gene locus.

Answer 48

The position of an allele on a chromosome.

Question 49

Define carrier.

Answer 49

An organism with a heterozygous genotype. They have one allele for a condition/ characteristic, but it is not expressed in the phenotype.

Question 50

Define monohybrid inheritance

Answer 50

Inheritance of one gene is responsible for the expression of the genotype.

Question 51

Compare and contrast the structures of DNA and RNA.

Answer 51

Similarites:
- The mononucleotides are joined by phosphodiester bonds in condensation reactions.
- Both made of mononucleotides composed of phosphate, a pentose suagr and an organic base.
- They both share three bases that are the same - adenine, guanine, cytosine.

Differences:
- DNA is double stranded whereas RNA is single stranded.
- DNA has thymine whereas RNA has uracil.
- The sugar in DNA whereas in RNA it is ribose.

Question 52

What are the 3 types of pre-natal screening?

Answer 52

Amniocentesis, chorionic villus sampling, NIPD.

Question 53

Describe amniocentesis.

Answer 53

Carried out when fetus is in uterus at 15-17 weeks. Fetal cells collected from the amniotic fluid surrounding fetus using a needle into the abdomen - dna extracted and analysed to detect gene mutation. 0.5-1% risk of miscarriage.

Question 54

Describe chorionic villus sampling (CVS).

Answer 54

Carried out when fetus is in uterus between 8-12 weeks. Fetal cells are collected from the placenta using a needle into abdomen or cervix into uterus via vagina - dna extracted and analysed to detect gene mutation. 1-2% risk of miscarriage.

Question 55

Describe non-invasive prenatal diagnosis (NIPD).

Answer 55

Carried out when fetus is in the uterus between 7-9 weeks. Analyses DNA fragments (cell free fetal DNA) from the mothers blood plasma to detect gene mutation.

Question 56

Describe pre-implantation genetic diagnosis (PGD).

Answer 56

Carried out during 8 cell embryo stage in IVF. One cell is taken from the embryo and dna is extracted and analysed to detect gene mutation.

Question 57

Describe the disadvantages/ implications of genetic screening.

Answer 57

Risk of miscarriage (amniocentesis + CVS)
False positive result could results in abortion of a healthy fetus.
Emotional and physical stress of choosing an abortion.