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A Level Biology Paper 1 > Section 1 - Chapter 2: Nucleic Acids > Flashcards

Section 1 - Chapter 2: Nucleic Acids Flashcards

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1
Q

What are 2 examples of nucleic acids

A
  • Ribonucleic acid (RNA)
  • Deoxyribonucleic acid (DNA)
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2
Q

What are the 3 components that make a nucleotide

A
  • A pentose sugar (called because it has 5 carbons)
  • A phosphate group
  • A nitrogen containing organic base. These are cytosine, thymine, uracil, adenine and guanine
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3
Q

How do nucleotides join together

A
  • The pentose sugar, phosphate group and organic base are joined in a condensation reaction to form a single nucleotide.
  • 2 Mononucleotides can be joined by condensation reactions between the deoxyribose sugar of 1 and phospahte group of the other. This bond is called a phosphodiester bond - dinucleotide
  • Continued linking - forms long chain = polynucleotide
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4
Q

What is the structure of RNA (ribonucleic acid)

A
  • Is a polymer made of nucleotides.
  • It is single, relatively short polynucleotide chain.
  • Pentose sugar = ribose
  • Organic bases = adenine, guanine, cytosine and uracil.
  • 1 type of RNA transfers genetic information from DNA to ribosomes. The ribosomes themselves are made up of proteins and another type of RNA. A 3rd type is involved in protein synthesis
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5
Q

What is the structure of DNA

A
  • In DNA the pentose sugar is deoxyribose and the organic bases are adenine, cytosine, guanine and thymine,
  • DNA is made of 2 strands of nucleotides.
  • Each of 2 strands is extremely long and joined by hydrogen bonds formed between certain bases.
  • Phosphate and deoxyribose molecules alternate to form uprights.
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6
Q

What are the base pairing in DNA

A
  • The bases on the 2 strands of DNA attach to eachother by hydrogen bonds.
  • Adenine pairs with Thymine (complementary)
  • Cytosine pairs with Guanine
  • Quantities of adenine and thymine = same, quantities of cytosine and guanine = same. However ratio of A,T and C,G vary
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7
Q

How does the DNA form a double helix

A
  • DNA molecule is formed from 2 separate strands wind around eachother to form a spiral (double helix)
  • They form the structural backbone of the DNA molecule (sugar phosphate backbone)
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8
Q

What are the differences between RNA and DNA

A
  • Shape: DNA is double stranded - twisted into a double helix and held together by hydrogen bonds. RNA is single stranded
  • Pentose Sugar: DNA is Deoxyribose sugar and RNA is Ribose sugar.
  • Bases: RNA- A,U,C,G and DNA - A,T,C,G
  • Size: RNA: relatively short and DNA: long
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9
Q

How is DNA a stable molecule

A
  • The phosphodiester backbone protects the more chemically reactive organic bases inside the double helix
  • Hydrogen bonds forms bridges between phosphodiester uprights. 3 hydrogen bonds between cytosine and guanine. 2 hydrogen bonds between A-T. Higher proportion of C-G = more stable
  • There are other interactive forces between the base pairs that hold the molecule together (base stacking)
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10
Q

How is DNA adapted to carry out its function

A
  • Very stable structure - passes generation to generation. Most mutations repaired
  • 2 strands joined by hydrogen bonds - allow separation for DNA replication and proteinsynthesis
  • Extremely large - carries immense amount of genetic info
  • Base pairs with helical cylinder (backbone) - genetic info protected by chemicals/forces
  • Base pairing leads to replication and transfer info to mRNA
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11
Q

What are the 4 requirements for Semi-conservative replication

A
  • The 4 types of nucleotide each with their bases
  • Both strands of the DNA molecule act as templates for the attachment of nucleotides
  • The enzyme = DNA polymerase
  • A source of chemical energy to drive the process
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12
Q

How does semi-conservative replication work

A
  1. Enzyme DNA helicase breaks hydrogen bonds between linking base pairs
  2. DNA helix separates into 2 strands and unwinds
  3. Each exposed polynucleotide strand act as a template for complemetary free nucleotides bind by specific base pairing
  4. Nucleotides are joined together in a condensation reaction by DNA polymerase to form “missing” strand on both originals
  5. Each of the new DNA molecules contain 1 original strand. Half the original DNA has been saved and built into each of the new DNA molecules
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13
Q

What is the other hypothesis called for DNA replication

A

Conservative Model

  1. Original DNA molecule remained intact and a separate daughter DNA copy was built up from new molecules of deoxyribose, phosphate and organic bases.
  2. Of the 2 molecules, one would be entirely new material and the other entirely original material
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14
Q

What are the 3 facts for Meselson and Stahl’s experiment for semi-conservative replication

A

The based their work on 3 facts:

  1. All the bases in DNA contain nitrogen
  2. Nitrogen has 2 forms (isotopes) 14N and 15N (heavier)
  3. Bacteria will incorporate nitrogen from their growing medium into any new DNA they make
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15
Q

What is the Structure of ATP

A
  • Adenine
  • Ribose
  • Phosphates - chain of 3 phosphates
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16
Q

How does ATP store enrgy

A
  • Bonds between the phosphate groups are unstable and have a low activation energy
  • When they break they release energy
  • ATP + H20 -> ADP + P (inorganic phosphate) + E
  • As water is used to convertATP to ADP - this is a hydrolysis reaction. Catalysed by enzyme ATP hydrolase
17
Q

How is ATP synthesised

A
  • The conversion of ATP to ADP is a reversible reaction and energy can be used to add an inorganic phosphate to ADP to re-form ATP.
  • Reaction catalysed by ATP synthase - condensation reaction.
  • Water is removes - condensation reaction
18
Q

In the synthesis of ATP. The addition of a phosphate molecule to ADP. It occurs in 3 ways.

A
  • In chlorophyll containing plant cells during photosynthesis (photophosphorylation).
  • In plant and animal cells during respiration (oxidative phosphorylation)
  • In plant and animal cells when phosphate groups are transferred from donor molecules to ADP (substrate- level phosphorylation)
19
Q

Why is ATP used as an immediate energy source rather than glucose

A
  • Each ATP molecule releases less energy than a glucose molecule.
  • therefore the reactions are smaller/more manageable quantities than glucose
  • The hydrolysis of ATP to ADP is a single reaction that releases immediate energy quicker. The breakdown of glucose is a longer series of reactions and therefore energy release takes longer
20
Q

What types of processes is ATP involved in

A
  • Metabolic processes - Energy needed to build up macromolecules
  • Movement - For muscle contraction
  • Active Transport - Provides energy to change the shape of carrier proteins in plasma membrane
  • Secretion - Form lysosomes for the secretion of cell products.
  • Activation of molecules - the inorganic phosphate released can be used to phosphorylate other compounds to make them more reactive - lowering the activation energy
21
Q

What is Meselson and Stahl’s experiment

(showed DNA replicated by semi-conservative replication. Used 2 isotopes heavy and light nitrogen)

A
  1. 2 samples of bacteria were grown for many generations. One in nutrient broth with light nitrogen other with heavy. As bacteria reproduced they took up nitrogen.
  2. A sample of DNA was taken from both and spun in centrifuge. Heavy settled lower from light.
  3. The bacteria grown in heavy broth taken and put in broth only containing light nitrogen. The replicated and centrifuged
  4. It turned out DNA settled in the middle showing DNA contained a mixture of light and heavy. If conservative - heavy would be at bottom light at top.
22
Q

What is the importance of water

A
  • Important for many metabolic reactions including condensation and hydrolysis reactions
  • Water is a solvent, metabolic reactions take place in solution (cytoplasm)
  • Helps with temperature control because it has a high latent heat of vaporisation/ specific heat capacity
  • Are very cohesive - helps water transport in plants.
23
Q

What is the structure of water

A
  • Made of 2 atoms of hydrogen and 1 atom of oxygen
  • Oxygen has a slight negative charge while hydrogen atoms have a slight positive charge. - dipolar
  • Positive pole of 1 water will be attracted to the negative pole of another water. The attractive force between molecules is a hydrogen bond. Allow water to stick together.
24
Q

Why does water have a high specific heat capacity

A
  • Because water molecules stick together
  • It takes more energy to separate them then would be needed if they didnt bond
  • Without hydrogen bonding - water would be a gas
  • It takes more energy to heat a mass of water. Water therefore acts as a buffer against sudden temperature change.
25
Q

What are the different properties of water

A
  • Important metabolite in many metabolic reactions, including condensation and hydrolysis reactions
  • Important solvent in which metabolic reactions occur in
  • Relatively high heat capacity - buffering change in temperature
  • Relatively large latent heat of vaporisation - providing a cooling effect with loss of water through evaporation
  • Strong cohesion between water molecules: supports column of water in transport in plants. Produces surface tension where water meets air.
26
Q

Why does water have a high latent heat of vaporisation and why is this important

A
  • Water evaporates when hydrogen bonds are broken
  • Allows water on the surface to escape as a gas. It takes a lot of energy to break H bonds - a lot of energy is used up when water evaporates.
  • This is useful as it means they can use water loss through evaporation to cool down without losing too much water. When water evaporates it carries away heat from the surface = cools down
27
Q

What are Inorganic ions

A
  • Ions that dont contain carbon (usually)
  • There are inorganic ions in solution in the cytoplasm of cells and in the body fluids of organisms.
  • Each ion has a specific role depending on its properties.
  • An ions role determines if it is found in high or low concs
28
Q

What are examples of inorganic ions

A
  • Iron ions in haemoglobin - The ion binds with the oxygen and releases it to respiring cells
  • Hydrogen ions - pH is calculated based on conc of H+. More H+, lower the pH.
  • Sodium ions - Co-transport of glucose and amino acids.
  • Phosphate ions - Phosphate ion is attached to another molecule its known as a phosphate group. Bond between phosphate groups that store energy in ATP. (DNA, RNA, ATP) Phosphate groups allow nucleotides to join = polynucleotides.

A Level Biology Paper 1 (15 decks)

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