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Bio AS paper 1 > DNA and genes > Flashcards

DNA and genes Flashcards

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1
Q

Features of RNA

A

-Single stranded
-Short in length
-Ribonucleic acid (has the oxygen on the second carbon unlike DNA)
- Bases are; Guanine, adenine, cytosine and uracil
-Acts as a messenger molecule, it transfers information that DNA contains into proteins

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2
Q

Features of DNA

A

-Double stranded
-Very long
-Deoxyribose (doesn’t have that extra oxygen like RNA )
-Bases; Adenine, cytosine, thymine and guanine

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3
Q

Function of DNA

A

-Contain genetic information for the development and function of the organism
-Each cell divides for growth and repair of damaged cells
-Each cell needs a full set of the DNA, 46 chromosomes

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4
Q

Give 3 structural differences between DNA and RNA

A

-DNA has 2 strands whereas RNA has only 1 strand
-DNA has the bases; cytosine, adenine, guanine and thymine. RNA has cytosine, adenine, uracil and guanine
-DNA is longer than RNA
-DNA has deoxyribose meaning it doesn’t have that extra oxygen on the second carbon like RNA

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5
Q

Describe the structure of a mononucleotide found in RNA

A

Has ribose sugar, phosphate and a base. The bases are uracil, adenine, cytosine and guanine

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6
Q

Describe how DNA replicates (6 marks)

A

-DNA helicase breaks through hydrogen bonds between complementary bases
-DNA strands separate
-Each new strand is used as a template
-Free nucleotides bind to complementary pairs using DNA polymerase
-Hydrogen bonds are reformed between these base pairs
-DNA ligase forms the phosphodiester bonds of the backbone
-This is known as ‘semi-conservative replication’

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7
Q

What is a gene?

A

A hereditary unit consisting of a sequence of DNA that occupies a specific location on a chromosome and determines a particular characteristic in an organism

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8
Q

Explain what an intron and and exon is

A

Exon - Coding section
Intron - Non coding section

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9
Q

Explain the process of translation

A

-mRNA binds to a ribosome tRNA. tRNA binds to a specific amino acid
-Complementary tRNA anticodons bind to mRNA codons and are held in place by hydrogen bonds.
-The ribosome joins the amino acids attached to the two tRNA molecules by a peptide bond
-tRNA molecules detach from amino acid
-Ribosome then moves along to next codon and forms a long polypeptide chain

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10
Q

Explain the process of transcription

A
  1. DNA helicase unzips complementary hydrogen bonds between bases
  2. This exposes the gene to be transcribed and a complementary copy of the gene is made by building mRNA
  3. Free nucleotides pair up with complementary bases of unzipped strand (via hydrogen bonds)
  4. The sugar phosphate groups of these RNA nucleotides are then bonded together using the enzyme RNA polymerase
  5. mRNA then moves through nuclear pore and attaches to ribosome for translation.
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11
Q

What is meant by degenerate code?

A

More than one triplet codes for the same amino acid

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12
Q

What is meant by non-overlapping code?

A

-Each triplet is only read once
-Triplets dont share any bases

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13
Q

What is meant by triplet code?

A

Each 3 bases codes for one amino acid.
Contains start and stop codons which either start or stop protein synthesis.

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14
Q

Give features of fibrous proteins

A

-Long parallel polypeptides
-Insoluble
-Very little tertiary structure
-Occasional cross-linkages which form microfibre for tensile strength
-Chains of amino acids

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15
Q

Give features of globular proteins.

A

-Complex tertiary or quaternary structures
-Many uses e.g. hormones, antibodies, carrier proteins
-Chains of amino acids joined by peptide bonds
-Molecule is held in place by hydrogen bonds
-Compact

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16
Q

Outline features of collagen and its role in the body

A

-Fibrous protein

-High tensile strength due to both hydrogen and covalent bonds.

-Collagen molecules are made from 3 polypeptides which forms strong collagen fibres

-Collagen forms the structures of bones, cartilage and connective tissue, a main component of tendons which connects muscle to bones. Found in artery walls.

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17
Q

What is an enzyme?

A

A biological catalyst which increases the rate of reaction by lowering activation energy of the reactions they catalyse, including both anabolic, catabolic, extracellular and intracellular reactions.

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18
Q

4 factors affecting enzyme controlled reactions.

A

Enzyme concentration
Temperature
Substrate concentration
PH

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19
Q

How does Ph effect the rate of enzyme controlled reactions?

A

Enzymes work in a specific range of Ph values. Values above or below this alter the bonds within the structure, hence the shape of its active site

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20
Q

How does enzyme concentration affect rate of enzyme controlled reactions?

A

Rate of reaction increases as enzyme concentration increases as there are more active sites to bind to. However, after a certain point, increasing enzyme conc has no effect on rate of reaction as there are more active sites than substrates so substrate concentration becomes the limiting factor.

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21
Q

How does substrate concentration affect rate of enzyme controlled reactions?

A

As substrate conc increases, rate of reaction increases. However, beyond a certain point rate of reaction no longer increases because enzyme concentration becomes the limiting factor.

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22
Q

How does temperature affect rate of enzyme controlled reactions?

A

As temperature increases, so does rate of reaction. however after a certain point, enzymes become denatured due to high temperatures.

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23
Q

What are the 5 different mutations?

A

Substitution (change in one base)
Insertion (adding in one base)
Deletion (taking out one base)
Duplication (adding the same base more than once)
Inversion (swapping the order of bases around )

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24
Q

Features of mRNA

A

-Copy of genetic code
-Moves out of the nucleus to ribosomes
-Acts as a template for translation

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25
Q

Features of tRNA

A

-Binds to an amino acid, takes amino acid to ribosome
-tRNA is specific for amino acid
-Holds the amino acid in place
-single stranded
-has ribonucleic acid

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26
Q

Compare and contrast the process of transcription with the process of DNA replication. (4 marks)

A

Similarities:
-Involves formation of phosphodiester bonds.
-Involve DNA helicase

Differences:
-Transcription uses RNA nucleotides and replication uses DNA nucleotides
-Transcription uses RNA polymerase whereas replication uses DNA polymerase`

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27
Q

Muscle cells contain globular and fibrous proteins.
Compare and contrast the molecular structures of globular and fibrous proteins.
(4)

A

Differences:
-Fibrous proteins are long parallel polypeptides whereas globular proteins are more compact and rounded
-Fibrous proteins have very little tertiary or quaternary structure whereas globular proteins have tertiary and quaternary structures.

Similarities:
-Both are chains of amino acids joined by peptide bonds
-Both have hydrogen/disulphide/ionic bonds

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28
Q

Explain primary structure

A

-Determined by DNA bases.
-Peptide bonds only
-The order and sequence of the amino acid
-DNA codes for shape, structure and function of the protein

29
Q

Explain secondary structure

A

-Natural attraction between these charges forming hydrogen bonds
-These hydrogen bonds are weak but there are lots of them
-Cause polypeptide to twist and coil into 3D shape
-Hydrogen is slightly positive charge, called alpha helix

30
Q

Explain tertiary structure

A

-Alpha helix can twist even more, folded into tertiary structure
-Disulphide bridges, ionic bonds, more hydrogen bonds and peptide bonds
-Disulphide bridges are found between cystine and cystine contain sulphur
-This bond is fairly strong and not easily broken
-Ionic bond is between the carboxyl group and the amino group. This changes with PH, denaturation.

31
Q

Explain quaternary structure

A

-Contain more than one polypeptide chain

(Imagine it as a ball of scribbles)

32
Q

Compare and contrast the molecular structures of globular and fibrous proteins

A

Differences:

-Fibrous proteins have little to no tertiary structure, whereas globular proteins have tertiary and quaternary structure.
-Fibrous proteins are long parallel polypeptides whereas globular proteins are folded into compact shapes
-Globular proteins have hydrophilic groups on the outside whereas fibrous proteins have hydrophobic groups inside.

Similarities:

-They are both chains of amino acids joined by peptide bonds.
- Both contain hydrogen holding the molecule in shape

33
Q

Describe the role of mRNA in protein synthesis (3 marks)

A
  • mRNA carries the genetic code for a protein
  • mRNA binds to ribosome
  • Complementary anticodon on tRNA will bind to codon on mRNA
  • Sequence of bases on mRNA determines the sequence of amino acids
34
Q

Compare and contrast the structure of a DNA double helix with the structure of tRNA (4 marks)

A

Similarities

-Both contain {nucleotides / phosphate group, pentose sugar and (organic) base} (1)
-Both contain {phosphodiester bonds/ hydrogen bonds between bases} (1)

Differences

-DNA is {double stranded/ a double helix} whereas tRNA is {single stranded /folded} (1)
-DNA contains {deoxyribose sugar / thymine} whereas tRNA contains {ribose / uracil} (1)

35
Q

Haemophilia is a disease that affects blood clotting. People with haemophiliaare sometimes given a protein called factor VIII. Factor VIII is an enzyme that is involved in the process of blood clotting.

Explain how a change in the primary structure of factor VIII could cause difficulties with blood clotting (4 marks)

A
  • (different primary structure) results in a different
    sequence of amino acids (1)

-Change in R groups changes { folding / bonding /
secondary structure / tertiary structure } (1)

-Changing { shape / charge } of the active site prevents
substrate from being able to bind (1)

  • { stopping / reducing } the production of fibrin (1)
36
Q

Name the process by which enzymes leave the cells of the pancreas and small intestine (1 mark)

A

Exocytosis

37
Q

The triglyceride in the diagram can combine with protein to form a lipoprotein

Explain the effect that large quantities of this lipoprotein would have on blood cholesterol levels (4 marks)

A

-Increased (blood) cholesterol (1)
-The triglyceride is saturated (1)
-The lipoprotein is an LDL (1)
-Lipoproteins transport cholesterol (1)

38
Q

Mutations to DNA can affect the structure of proteins produced in the cell

Removing one base from a DNA sequence will affect the primary structure of a protein

Changing one base for another may not affect the primary structure of a protein

Explain why these two types of mutation have different effects on protein structure (4)

A

-Deletion could affect every codon (on the mRNA) / substitution will only affect one codon (1)

-Deletion more likely to affect the position of { stop codon/ start codon } (1)

-Deletion results in a different sequence of amino acids / substitution may not affect the sequence of amino acids (1)

-Substitution may code for the same amino acid (1)

39
Q

State what is meant by the term allele (2)

A

-Alternative form of a gene (1)
-Found at the same locus (on a chromosome) (1)

40
Q

Explain one ethical issue relating to the use of prenatal genetic screening (2)

A

It may result in a choice of an abortion (1)
-It is unethical to cause the death of a foetus (1)

41
Q

Explain how a change of one amino acid could lead to a change in the structure and properties of the haemoglobin protein (4)

A

-Different sequence of amino acids / primary structure (1)
-A different amino acid will have a different R group (1)
-Therefore) secondary / tertiary / quaternary structure will change (1)
-Due to a change in hydrogen bond holding molecule in its three-dimensional shape (1)
-Haemoglobin may not bond to oxygen (1)

42
Q

Give one function of the glycoproteins found in the cell surface membrane (1)

A

cell - cell recognition

43
Q

Describe how mRNA is synthesised at a template strand of DNA (2)

A

-Nucleotides align with complementary bases (on DNA) (1)

-RNA nucleotides joined together by
phosphodiester bonds} (1)

44
Q

Describe the differences between the structure of DNA and the structure of RNA (3)

A

-DNA is double stranded whereas RNA is single stranded (1)
-DNA contains deoxyribose whereas RNA contains ribose (1)
-DNA contains {thymine / T} whereas RNA contains {uracil / U} (1)

45
Q

Features of Cystic fibrosis

A

-Cystic fibrosis is a genetic disorder caused by a mutation of a single gene which
codes for the CTFR protein .
-CTFR is a channel protein which transports chloride ions out of cells of the respiratory tract and into the mucus
-This makes the mucus watery as it causes water to move into mucus by osmosis. Therefore, a mutation in this gene makes the mucus very thick , as a mutant CTFR protein is less efficient at transporting chloride ions.
-Sticky and thick mucus causes many problems in gas exchange, reproducing and digestion .

46
Q

Effects of CF on reproductive system

A

● Cervical mucus prevents the sperm from reaching the egg.
● In men, the sperm duct is blocked with mucus, meaning that sperm produced cannot leave the testes.

47
Q

Effects of CF on respiratory system

A

● Build-up of mucus in the lungs traps bacteria, thus increasing the risk of infection.
● Build-up of mucus in the airways decreases the surface area of alveoli involved exposed to fresh air, therefore reducing the surface area for gas exchange.

48
Q

Effects of CF on digestive system

A

● The pancreatic duct which connects the pancreas to the small intestine can become blocked with mucus, so the digestive enzymes do not reach the small intestine. As a result food is not properly digested, so fewer nutrients are absorbed.
● The mucus lining is very thick, thus reducing the absorption of
nutrients.
● Mucus can cause cysts to form in the pancreas and damage the insulin producing cells, thus leading to diabetes.

49
Q

Features of amniocentesis

A

-Needle extracts cells from amniotic fluid
-Prenatal, 15-20 weeks
- 1% risk of miscarriage
+Allows parents to make informed decisions (prepare for care)
-Takes 2-3 weeks for results to come back and it is done quite late on in pregnancy + waiting time makes the decision harder

50
Q

Features of CVS

A

-Testing a sample from the placenta
-Prenatal, 11-14 weeks
-1-2% risk of miscarriage
+Rapid results (7-10 days)
+Needle means a large sample can be obtained and its detected early on
-Cannot pick up disorders on male X chromosome as it is inactive in the placenta cells

51
Q

Features of PiGD

A

-Checking genes/chromosomes of the embryos before IVF happens
-Pre implantation
-Evidence suggests PGD does no harm
+Avoids abortion and reduces/eliminates the chances that the child has CF
-Cells are taken from embryo for testing, discarding embryo is unethical

52
Q

Describe the role of CFTR protein in ensuring that the mucus produced in the lungs has the right consistency (3 marks)

A

-Chloride and sodium ions leave cells (through CFTR channel protein)

-Increasing the solute concentration in the mucus

-Water moves out the cells via osmosis

53
Q

What causes Cystic Fibrosis?

A

-Caused by faulty chromosome 7 on CFTR channel protein
-Caused by a mutation
-Carried on a recessive allele

54
Q

Name of the pre-natal genetic screening test that is carried out in the 10th week of pregnancy

A

Chronic villus sampling

55
Q

Discuss the ethical issues relating to the use of genetic screening during pregnancy (2)

A
  • 1-2% chance risk of miscarriage
  • Risk of false positive result
56
Q

Explain why someone would rather use PiGD than amniocentesis (2)

A

-Fewer ethical issues with PiGD as the embryo has not been implanted

  • No risk of miscarriage from PGD but there is from amniocentesis
57
Q

Compare and contrast the use of PiGD and amniocentesis (4)

A
  • Both look for any genetic condition so parents can make an informed decision
  • PGD is before implantation, amniocentesis is after implantation
  • Increased risk of miscarriage with amniocentesis
  • PGD tests the embryo but amniocentesis tests amniotic fluid
58
Q

Explain how a change of one amino acid could lead to a change in the structure and properties of a protein (3)

A
  • Different sequence of amino acids is produced
  • Which produces a different R group
  • Therefore a different secondary/tertiary/quaternary structure
59
Q

What is the function of collagen in the blood-gas barrier

A

To provide strength

60
Q

Describe the structure of collagen (3)

A
  • Collagen has 3 polypeptide chains
  • Chains coiled around each other
  • Cross linkages between the chains
61
Q

Compare and contrast the structures of globular proteins and fibrous proteins (4)

A

Similarities:
- Both are chains of amino acids joined by peptide bonds
- Both contain hydrogen bonds holding the molecule in shape

Differences:
- Globular have tertiary structure whereas fibrous have little to no tertiary structure
- Globular are spherical and fibrous are long strands

62
Q

Explain why enzymes which are incorrectly folded cannot carry out their function (3)

A
  • If protein is not folded correctly the tertiary structure would be different
  • Therefore the active site of the enzyme would not fit/bind with the substrate
  • Therefore it cant catalyse the reaction
63
Q

Mucopolysaccharides can be broken down by enzymes

Describe how an enzyme could break down the polysaccharide component of mucopolysaccharides (2)

A

Hydrolysis of glycosidic bonds

64
Q

An enzyme hydrolyses phospholipids, releasing fatty acids

Describe how the structure of phospholipase allows it to hydrolyse phospholipids (4)

A
  • The structure of the enzyme is determined by the sequence of amino acids
  • Tertiary structure provides active site
  • Active site is complementary to part of phospholipid
  • The enzyme breaks ester bonds between glycerol and fatty acids
65
Q

Explain what is meant by the term semi-conservative DNA replication (2)

A
  • Doubling of the DNA
  • With each original DNA strand acting as a template onto which a new strand is formed
  • DNA formed contains one original strand and one new strand of DNA
66
Q

Explain why cystic fibrosis affects digestion (3)

A
  • Produces sticky mucus
  • This blocks flow of enzymes from pancreas
  • Which reduces digestion, reducing the flow of bile
67
Q

Explain why cystic fibrosis affects the rate of oxygen uptake in the lungs (3)

A

-Thick sticky mucus which cant be moved by cilia
-Restricting air flow through bronchi
-Increasing diffusion distance/reducing surface area for gas exchange in the alveoli

68
Q

Explain how chloride ions move in and out the apical and basal membranes (4)

A

Basal membrane:
- Chloride ions move by active transport into the cell, against the concentration gradient using energy from ATP

Apical membrane:
- Chloride ions move out the cell by facilitated diffusion down the concentration gradient

69
Q

Explain the movement of chloride ions in a healthy person and a person with CF

A

Person with CF:
Chloride ions becomes trapped in cells.
Without the proper movement of chloride, water cannot hydrate the cellular surface.
This leads the mucus covering the cells to become thick and sticky.

Healthy person:
Chloride ions move through basal membrane via facilitated diffusion
Sodium ions move through the apical membrane via active transport

Bio AS paper 1 (4 decks)

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