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AS Biology > Topic 1B - More Biological Molecules > Flashcards

Topic 1B - More Biological Molecules Flashcards

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1
Q

Name two types of nucleic acid and where they are found/what they all do?

A
  1. DNA (deoxyribonucleic acid) and RNA (ribonucleic acid)

2. They are found in living cells and they all carry information

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2
Q

What is the main function of DNA?

A

To store genetic information (all the instructions an organism needs to grow and develop from a fertilised egg to a fully grown adult)

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3
Q

What is the main function of RNA?

A

transfers genetic information from DNA to ribosomes

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4
Q

What are ribosomes made of and briefly describe how they make proteins?

A
  1. Ribosomes are made from RNA and proteins

2. They read the RNA to make polypeptides in a process called ‘translation’

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5
Q

DNA and RNA are polynucleotides, what are polynucleotides?

A

polymers of nucleotides

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6
Q

What is a nucleotide made out of?

A
  1. A phosphate group
  2. A pentose sugar (sugar with 5 carbon atoms)
  3. A nitrogen-containing organic base
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7
Q

Describe the structure of a DNA nucleotide

A
  1. The pentose sugar in a DNA nucleotide is called deoxyribose
  2. Each DNA nucleotide has the same phosphate group and sugar, but the base can vary
  3. The four bases are adenine, thymine, guanine, cytosine
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8
Q

Describe the structure of a RNA nucleotide

A

same as DNA except the pentose sugar is a ribose sugar and uracil replaces thymine as a base.

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9
Q

How do nucleotides join up?

A

They join up via condensation reaction between the phosphate group of one nucleotide and the sugar of another
- This forms a phosphodiester (one phosphate group, two ester bonds)

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10
Q

What do you call the chain of sugars and phosphates in a polynucleotide?

A

The sugar-phosphate backbone

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11
Q

Describe the structure of DNA?

A
  1. 2 DNA polynucleotides strands join together by hydrogen bonding between the bases
  2. Complementary base pairing: A-T, C-G (equal amounts of bases in a pair)
  3. 2 hydrogen bonds between A and T, 3 hydrogen bonds between C and G
  4. Two antiparallel (running in opposite directions) polynucleotide strands twist to form DNA double helix
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12
Q

What were the basic ideas about DNA in the 1800s?

A
  • Was first observed in the 1800’s but scientists doubted it carried genetic code as it had relatively simple chemical composition.
  • Some argued that genetic info must be carried by proteins - which are much more chemically varied
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13
Q

What were the ideas about DNA in the 1900’s

A
  • In 1952, experiments showed that DNA was the carrier of the genetic code.
  • Watson and Crick also determine the double helix structure, which helps DNA to carry out its function and also suggest the semi-conservative DNA replication theory
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14
Q

Describe the polynucleotide chain of RNA.

A
  • RNA is a relatively short polynucleotide chain; its much shorter than most DNA polynucleotides
  • its made from a single polynucleotide chain (not a double one)
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15
Q

What is semi-conservative replication and why is it called ‘semi-conservative’?

A

When DNA copies itself before cell division so that each new cell has the full amount of DNA

  • It is called semi conservative as half of the strands in each new DNA molecule are from the original DNA molecule
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16
Q

Semi conservative replication means there is ……… continuity between generations of cells? why?

A
  • Genetic

- cells produced by cell division inherit their genes from their parent cells

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17
Q

Describe the process of semi conservative replication

REFR TO DIAGRAMS

A
  1. Enzyme DNA helicase breaks hydrogen bonds between bases on polynucleotide DNA strands, making helix unwind to form 2 single strands
  2. Each original single strand acts as template for new strand. Complementary base pairing means free-floating DNA nucleotides are attracted to their complementary exposed bases on each original template strand (A-T C-G)
  3. Condensation reactions join nucleotides of new strands together - catalysed by DNA polymerase. Hydrogen bonds form between bases on original and new strands
  4. Each new DNA molecule contains one strand from original DNA and one new strand
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18
Q

How are the ends of a DNA strand different in structure?

A

One end is called the 3’ (3 prime), whilst other end is called the 5 prime.
- They run in opposite directions (they’re antiparallel)

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19
Q

Describe how DNA polymerase is related to the 3’ and 5’

A
  1. The active site of DNA polymerase is only complementary to 3’ end of new strand - so enzymes can only add nucleotides to the new strand at 3’ end
  2. So new strand is made at 5’ to 3’ direction and that DNA polymerase moves down the template strand in 3’ to 5’ direction (as strands are antiparallel, enzyme will move in opposite directions, for each strand)
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20
Q

Who were the two scientists who proved the semi-conservative replication theory?

A

Meselson and Stahl

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21
Q

What were the two types of nitrogen used in Meselson and Stahls experiment?

A

Light nitrogen (14N) and heavy nitrogen (15N

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22
Q

Describe part 1 of the semi-conservative method carried out by Meselson and Stahl.

A
  1. 2 bacteria samples were grown - one in nutrient broth containing light nitrogen and one in one containing heavy nitrogen. As bacteria reproduced, they took up nitrogen from broth to help make nucleotides for new DNA so nitrogen naturally became part of DNA
  2. Sample of DNA was taken from each batch of bacteria, and spun in centrifuge, DNA from heavy nitrogen batch settled lower in tube than DNA from light nitrogen batch
  3. Then bacteria from heavy nitrogen broth was taken out and put in light nitrogen broth. Bacteria was left for one round of DNA replication and then another DNA sample was taken out and spun in centrifuge
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23
Q

Describe part 2 of the semi-conservative method carried out by Meselson and Stahl. (starting from ‘if replication was conservative…’

A
  1. If replication was conservative, original heavy DNA would still be together and would settle at the bottom, and new light DNA would settle at the top
  2. If replication was semi-conservative, new bacterial DNA molecules would contain one strand of the old DNA containing heavy nitrogen and one new strand containing light nitrogen. So DNA would settle out between where the light and heavy nitrogen DNA settled out
  3. The DNA settled out in the middle, showing that DNA molecules contined a mixture of heavy and light nitrogen. The bacterial DNA had replicated semi-conservatively in the light nitrogen
24
Q

What effect did Meselson and Stahls experiment have on other scientists?

A

It encouraged other scientists to carry out experiments showing that semi-conservative replication was the universal method for DNA replication in all living things

25
Q

Outline 4 reasons why water is vital to living organisms.

A
  1. Water is a metabolite in loads of important metabolic reactions, including condensation and hydrolysis reactions
  2. Water is a solvent and most metabolic reactions take place in solutions (e.g. cytoplasm of eukaryotic and prokaryotic cells) so water is essential
  3. Water helps with temperature control as it has a high latent heat of vaporisation and a high specific heat capacity
  4. Water molecules are very cohesive (they stick together), which helps water transport in plants as well as transport in other organisms
26
Q

Describe the structure of water molecules (DIAGRAM)

A
  1. One oxygen atom + 2 hydrogen atoms (joined by shared electrons) makes a molecule of water
  2. Shared negative hydrogen electrons are pulled towards oxygen atom, leaving other side of each hydrogen atom with a slight positive charge
  3. Unshared negative electrons on oxygen atom give it a slight negative charge
  4. This makes water a polar molecule with a partial negative charge on one side and a partial positive charge on the other
  5. The slightly negatively charged oxygen atoms attract the slightly positively charged hydrogen atoms of other water molecules
  6. This is called hydrogen bonding and gives water some of its useful properties
27
Q

Describe how water is an important metabolite

A
  1. Many metabolic reactions involve a condensation/ hydrolysis reaction
  2. A hydrolysis reaction requires a water molecule to break a bond (e.g. when energy from ATP is released) and a condensation reaction releases a molecule of water as a new bond is formed (e.g. when amino acids are joined together to form polypeptides)
28
Q

Describe how water has a high latent heat of vaporisation and why this is useful.

A
  1. It takes a lot of energy to break hydrogen bonds between water molecules
  2. So water has a high latent heat of vaporisation - a lot of energy is used up when water evaporates
  3. This is useful for organisms as it means they can use water loss through evaporation to cool down (sweating) without losing too much water
29
Q

What is a:

  • metabolite?
  • metabolic reaction?
A
  • Metabolite: a substance involved in a metabolic reaction

- Metabolic reaction: A chemical reaction that happens in a living organism to keep the organism alive

30
Q

Describe how water can buffer/resist changes in temperature and why this is useful.

A
  1. The hydrogen bonds between water molecules can absorb a lot of energy
  2. So water has a high SHC - it takes a lot of energy to heat up
  3. This is useful for organisms as it means that water doesnt experience rapid temp changes. This makes water a good habitat as the temp under water is likely to be more stable than on land - helping them to maintain a contant internal body temp.
31
Q

Describe how water polarity makes it a good solvent

A
  1. A lot of important substances in metabolic reactions are ionic (e.g. salt). This means they’re made from one positively charged atom/molecule and one negatively charged atom/molecule
  2. As water is polar, the positive end of a water molecule will be attracted to the negative end ion, and vice versa
  3. This means the ions will get totally surrounded by water molecules - they’ll dissolve
  4. So waters polarity makes it a useful solvent
32
Q

Define the term cohesion

A

Cohesion is the attraction between molecules of the same type

33
Q

How are water molecules cohesive and why is this useful?

A
  1. Water molecules are cohesive as they’re polar
  2. Strong cohesion helps water to flow, making it good for transporting substances e.g water travel in xylem
  3. Strong cohesion also means that water has a high surface tension when it comes into contact with air. This is why sweat forms droplets, which evaporate from the skin to cool us down. It’s also why pond skaters and some insects can ‘walk’ on the surface of water.
34
Q

What is ATP made from? (DIAGRAM)

A

adenosine, a ribose sugar and 3 phosphate groups. (a nucleotide derivative as its a modified form of a nucleotide)

35
Q

What happens after ATP is made?

A
  1. Once made, ATP diffuses to the part of the cell that needs energy
  2. Energy is stored in high energy bonds between the phosphate groups
  3. It’s released via hydrolysis reactions`
36
Q

What is the main function of ATP?

A

It is immediate source of energy in a cell

37
Q

What happens to ATP when energy is needed by a cell?

A
  1. ATP is broken down into ADP (adenosine diphosphate) and Pi (an inorganic phosphate) in a hydrolysis reaction
  2. The reaction is catalysed by the enzyme ATP hydrolase
38
Q

How does ATP hydrolysis affect energy-requiring reactions?

A

ATP hydrolysis can be coupled with energy-requiring reactions so energy released can be used directly to make the coupled reaction happen, rather than being lost as heat

39
Q

What can we do with the released inorganic phosphate? (from our hydrolysis reaction)

A

It can be added to another compound in phosphorylation to make the compound more reactive

40
Q

How is ATP resynthesised after it is used up? (DIAGRAM)

A

It is resynthesised in a condensation reaction between ADP and Pi, using energy from an energy-releasing reaction.
- This reaction happens during respiration
& photosynthesis
- It is catalysed by the enzyme ATP synthase

41
Q

What is an ion?

A

an atom that has an electric charge

42
Q

What is an anion?

A

An ion with a negative charge

43
Q

What is a cation?

A

An ion with a positive charge

44
Q

What is an inorganic ion?

A

An ion that doesnt contain any carbons (although there are exceptions to this rule)

45
Q

Where are inorganic ions found?

A
  • In solution: In the cytoplasms of cells and in bodily fluids of organisms
46
Q

What factor determines the role of an inorganic ion?

A

The properties of an ion determines its role

47
Q

What can the role of ions determine?

A

Whether the ion is found in high or low concentrations

48
Q

Describe the importance of iron ions?

A

They are an important part of Haemoglobin:
1. Haemoglobin is a large protein that carries oxygen around the body, in the red blood cells
2. It’s made up of four different polypeptide chains, each with an iron ion (Fe2+) in the centre
3. The Fe2+ BINDS to the oxygen in haemoglobin
and temporarily becomes an Fe3+ ion, until oxygen is released

49
Q

Describe the importance of hydrogen ions?

A

Hydrogen ions determine pH of a solution

  • The more H+ ions present, the lower the pH
  • Enzyme controlled reactions are all affected by pH
50
Q

Describe the importance of phosphate ions?

A

They are an essential component of ATP and DNA

  • When a phosphate ion is attached to another molecule, it is known as a phosphate group
  • DNA, RNA and ATP all contain phosphate groups
  • Its the bond between phosphate groups that store energy in ATP
  • The phosphate groups in DNA and RNA allow nucleotides to join up to form polynucleotides
  • It activates enzymes by binding to it.
51
Q

Describe the importance of calcium ions?

A
  • They harden body parts e.g. bones, teeth, exoskeleton
  • Regulates transmission of impulses between neurones.
  • Stimulates muscle contraction.
  • Regulates the opening and closing of protein channels, to change the permeability of the membrane.
  • It activates enzymes by binding to it.
  • Helps form blood clots.
  • Helps form middle lamella in between plant cell walls.
52
Q

Describe the importance of sodium ions.

A
  • Helps regulate osmotic pressure, by causing water to move into plant cell so that it can be turgid. (this prevents plant from being dehydrated)
  • Regulates absorption of water in kidney (Kidney filters blood out, and when sodium reenters kidney, water follows it.
  • Regulating nerve impulses.
  • Helps maintain pH of the body.
  • Sodium-potassium pump/helps transport glucose and amino acids out of lumen.
53
Q

Describe the importance of potassium ions.

A
  • Helps regulate osmotic pressure(same reason as Na+)
  • Sodium-potassium pump
  • Helps maintain pH of the body.
  • Helps plants grow healthy leaves and flowers.
  • Used to make proteins and glycogen
  • Used to hydrolyse glucose in respiration,
54
Q

Describe the importance of ammonium ions/nitrate ions

A
  • Nitrogen in amino acids/DNA and RNA bases/vitamins/chlorophyll come from ammonium/nitrate ions
  • Ammonia converted to ammonium by accepting H+ so ammonium helps buffer solution by taking in H+ ions
  • Nitrogen cycle
55
Q

Describe the importance of hydrogencarbonate ions?

A
  • CO2 combines with water to form hydrogencarbonate, so CO2 can be converted into soluble hydrogencarbonate form, so that it can easily be transported around the body .
56
Q

What is adhesion?

A

The tendency of water molecules to bind to molecules other than water

AS Biology (12 decks)

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