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Biology > Nucleic acids, ATP and Water A1 > Flashcards

Nucleic acids, ATP and Water A1 Flashcards

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1
Q

Explain how DNA replicates.

A
  1. hydrogen bonds broken
  2. semi-conservative replication / both strands used as templates
  3. specific base pairing / nucleotides line up complementary
  4. DNA polymerase joins the nucleotides together
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2
Q

What is the role of DNA and RNA.

A
  1. DNA holds genetic information
  2. RNA transfers genetic information from DNA to ribosomes
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3
Q

Describe a polynucleotides formation.

A
  1. polynucleotide strands are formed when many nucleotides (monomers) link to form a long chain (polymer)
  2. during a condensation reaction
  3. forming a phosphodiester bond between phosphate group of one nucleotide to the pentose sugar in the next
  4. this is a covalent bond and makes the sugar-phosphate backbone strong
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4
Q

Compare and contrast DNA and RNA.

A
  1. DNA is double stranded / RNA is single stranded
  2. long molecule / short molecule
  3. deoxyribose sugar / ribose sugar
  4. thymine / uracil
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5
Q

Describe the structure of DNA
(8)

A
  1. sugar-phosphate backbone / double stranded helix - provides strength and stability, protects hydrogen bonds
  2. long/large molecule so can store lots of information
  3. helix/coiled so compact
  4. base sequence allows information to be stored/ base sequence codes for amino acids/proteins
  5. double stranded to semi-conservative replication can occur / strands can act as templates
  6. complementary base pairing (A+T, G+C) so identical copies can be made (accurately)
  7. weak hydrogen bonds for replication / strand separation (unwinding)
  8. many hydrogen bonds so stable/strong
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6
Q

Describe semi-conservative replication.

A
  1. DNA helicase
  2. causes H bonds to break and strand separate
  3. both strands act as a template
  4. free nucleotides attach
  5. complementary base pairing A+T, C+G
  6. DNA polymerase joins nucleotides on new strand
  7. H-bonds reform
  8. semi-conservative replication / new DNA molecules contain one old strand and one new strand (identical to original DNA)
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7
Q

Explain why DNA polymerase only works in one diretion?

A
  1. DNA has anti-parallel strands
  2. the shape of nucleotides is different
  3. enzymes have an active site with a specific shape
  4. only substrates with a complementary shape can bind with the active site of DNA polymerase (it can only bind with the 3’ end as the 5’ end is a different shape)
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8
Q

Explain why scientists initially doubted that DNA was the genetic code.

A
  1. scientists thought DNA was too simple a molecule to carry genetic information
  2. they though proteins were what carried genetic information
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9
Q

Evaluate Watson and Cricks model and how other scientists verified their ideas.

A
  1. the theory was called semi-conservative replication of DNA (hydrogen bonding between complementary pairs)
  2. however other theories suggested that both DNA strands were new in the double stranded helix (conservative) rather than one original and one new strand.
  3. Watson and Crick were later proved right by the Meselson Stahl experiment.
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10
Q

Explain the method of the Meselson and Stahl experiment. (summarise)
(8)

A
  1. bacteria are grown in broth containing the heavy 15N nitrogen isotope
  2. DNA contains nitrogen in its bases
  3. as the bacteria replicated, they used N from the broth to make new DNA nucleotides
  4. after some time, the culture of bacteria has DNA containing only heavy (15N) nitrogen
  5. a sample of DNA from the 15N culture of bacteria was spun in a centrifuge
  6. this showed DNA containing heavy N settles near bottom of tube
  7. bacteria containing only 15N was taken out and added to broth containing only lighter 14N
  8. the bacteria were left for enough time for one round of DNA replication to occur before their DNA was extracted and spun in centrifuge
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11
Q

Explain the results of the Meselson and Stahl experiment. (summarise)

A
  1. if semi-conservative replication had occurd, all DNA molecules would now contain both heavy and light (15N and 14N) and therefore would settle in the middle of the tube (one DNA strand from original(heavier) and one new(lighter))
  2. this experiment confirmed the DNA had undergone semi-conservative replication
  3. the DNA from this second round of centrifugation settles in the middle of the tube, showing each DNA molecule contained a mixture of heavy and light N isotopes
  4. if more rounds of replication were allowed to take place, the ratio of 15N:14N would go from 1:1 after first round of replication, to 3:1 after second round and 7:1 after third.
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12
Q

Draw and label a diagram of ATP.

A

P-P-P(phosphate group) - SUGAR (ribose) -BASE(adenine)
(P-P-P - Ribose - Adenine)

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13
Q

Describe the role of ATP.
Give examples of processes it is used in.

A

ATP (adenine triphosphate) consists of a nitrogenous organic base and three phosphate groups and is used as the energy source in plants and animals to carry out essential life processes eg protein synthesis, muscle contraction, active transport

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14
Q

What is ATP formed by?

A

ATP = ADP + Pi
(reversible reaction too)

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15
Q

ATP is so useful because…
(6)

A
  1. releases energy in small/manageable amounts (not lost in heat)
  2. single bond broken (in one step)
  3. immediate energy compound / energy available rapidly
  4. phosphorylates / adds phosphate
  5. makes phosphorylated substances more reactive / lowers activation energy
  6. reformed / made again / does not leave cells
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16
Q

Describe how ATP is re-synthesised in cells?

A
  1. ADP + Pi
  2. ATP synthase
  3. during respiration
17
Q

Which enzyme is involved in hydrolysing ATP into ADP + Pi?

A

ATP hydrolase

18
Q

Give five properties of water that are important in biology and explain.
(5)

A
  1. polar molecules - dissolves charged particles / acts as a universal solvent
  2. metabolite - involved in metabolic reactions (condensation/hydrolysis)
  3. cohesion between molecules - provides surface tension / prevents columns of water breaking
  4. high specific heat capacity - reduces fluctuations in temperature of water bodies
  5. high latent heat of evaporation - evaporation of smalls amounts of water to cool organisms
19
Q

Suggest why water becomes lighter as it expands.
(2)

A
  1. density = mass ÷ volume
  2. ice has the same mass as water but greater volume
20
Q

Suggest one biological advantage of water becoming lighter as it expands.
(3)

A
  1. ice is colder than water
  2. ice floats on water (as it is lighter)
  3. reduces freezing of water below ice
21
Q

Scientists looking for extra-terrestrial life are looking for planets with evidence of free water.
Explain why water is considered so important for life to occur.
(7)

A
  1. life is though to have evolved through water
  2. water provides support for bodies organisms
  3. its a major component of cytoplasm
  4. universal solvent / metabolic reactions occur here
  5. its a metabolite / a reactant in many reactions
  6. stabilises external temperatures
  7. important in cooling / stabilising internal temperatures or organisms
22
Q

Describe the role of hydrogen, nitrate, potassium and magnesium ions in living organisms.

A
  1. hydrogen ions - hydrogen bonds (to form DNA and enzymes, concentration of ions affects PH (acid/alkali)
  2. nitrates - nitrogen bases in DNA, RNA, ATP, amino acids - proteins, enzymes
  3. potassium - plant growth, nervous system
  4. magnesium - makes chlorophyll in plants (photosynthesis)
23
Q

Describe the role of iron ions, sodium ions and phosphate ions in cells.

A
  1. iron ions are used to attach haemoglobin to red blood cells, so then can carry more oxygen around the body for muscle movement etc
  2. phosphate ions are used in nucleotides (phosphate group) such as ATP, here when broken they release energy for things like protein synthesis etc. They help code for amino acids to make proteins (enzymes) in RNA.
  3. Sodium ions help maintain a concentration gradient of water in and out of cells, preventing osmotic lysis.
24
Q

Label the components of a nucleotide.

A

Phosphate group - Pentose sugar(deoxyribose or ribose) - nitrogenous base

Biology (27 decks)

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