Nucleic Acids Flashcards
1
Q
What does DNA stand for?
A
Deoxyribonucleic Acid
2
Q
What is the function of DNA and RNA?
A
- They are both found in all living cells and carry information.
- DNA stores genetic information so a fertilised egg can grow and develop into a grown adult.
- RNA has a similar structure to DNA and transfers genetic information from DNA to ribosomes.
3
Q
What are nucleotides?
A
DNA and RNA are polymers of nucleotides. Their structure is a phosphate group attached to a pentose sugar attached to a nitrogen-containing organic base.
4
Q
What is the structure of DNA?
A
- It is a polynucelotide (phosphate group, base and deoxyribose pentose sugar). Its bases vary and can be adenine, thymine, cytosine or guanine.
- double helix shape (two strands form a spiral)
- long and tightly-coiled, holding lots of genetic information
- sugar-phosphate backbone provides stability and protection
5
Q
What are double and single ring bases?
A
- Adenine and guanine are purine bases, which are double ringed.
- Cytosine, thymine and uracil are pyrimidine bases, which are single ringed.
- a smaller pyrimidine base always bonds to a larger purine base to maintain a constant distance between the two polynucleotides.
6
Q
What is a polynucleotide structure?
A
- nucleotides join together by condensation reactions between the phosphate group of one and the pentose sugar of another.
- Therefore, the phosphate group is bonded to two sugars by ester bonds, creating a phosphodiester bond.
- This created a chain called a sugar-phosphate backbone.
7
Q
What is the history of determining DNA structure?
A
- Rosalind Franklin suggested DNA’s helical structure as she studied it by x-ray diffraction.
- Watson and Crick found that DNA was double-stranded, winning them the 1962 Nobel Prize.
8
Q
How does DNA have a double helix shape?
A
- the two DNA polynucleotide strands are joined by weak hydrogen bonds.
- A pairs with T by two hydrogen bonds
- C pairs with G by three hydrogen bonds
- the strands are antiparallel (one pointed up, one pointed down), which twists them into a double helix
9
Q
What does RNA stand for?
A
Ribose Nucleic Acid
10
Q
What types of RNA are there?
A
- messenger RNA (mRNA) –> transfers genetic information from nucleus to ribosomes
- ribosomal RNA (rRNA) –> combined with protein, it forms a structural part of ribosomes
- transfer RNA (tRNA) –> involved in protein synthesis
11
Q
What is the structure of RNA?
A
- made of nucleotides (ribose sugar, phosphate group, base) to form a polynucleotide strand with a sugar-phosphate backbone
- single-stranded
- contains the base uracil instead of thymine
- RNA is shorter than DNA
12
Q
What is messenger RNA?
A
A triplet of DNA is converted into mRNA, which is called transcription, which is the first step of protein synthesis. This will create a sequence of bases complementary to the DNA strand.
13
Q
What is transfer RNA?
A
Amino acids (base triplets) attach to tRNA in the cytoplasm, creating an anticodon, which is complementary to the mRNA codons (triplets)
14
Q
What are some suggested mechanisms that replicate DNA?
A
- conservative
- semi-conservative (how DNA replicates)
- dispersive
15
Q
Why does DNA replicate?
A
- it replicates before cell division so every cell has the full amount of DNA
- semi-conservative replication as half of new strands in each new DNA molecule comes from the original molecule
- this replications means there is genetic continuity, reducing risk of mutations
16
Q
How is DNA replicated?
A
- enzyme DNA helicase breaks hydrogen bonds between bases on two strands of DNA to unwind and separate the helix.
- the separate strands act as templates, allowing complementary free floating DNA nucleotides to attract.
- the nucleotides are joined together by condensation reactions, catalysed by DNA polymerase.
- hydrogen bonds between the two polypeptide strands form a new double helix for each original one.
17
Q
What role does DNA polymerase have in DNA replication?
A
- only joins nucleotides together in the 5’ to 3’ direction (two ends of a DNA strand), by moving in the 3’ to 5’ direction
- DNA ligase joins up any areas DNA polymerase doesn’t
18
Q
What evidence is there for semi-conservative DNA replication?
A
- Meselson and Stahl conducted an experiment in which they grew a heavy nitrogen isotope (15N) and a lighter nitrogen isotope (14N) separately in E. coli.
- This meant that as the bacteria grew, it took up the different nitrogen isotopes and made DNA nucleotides.
- After samples were spun in a centrifuge, the heavier isotope bacteria settled lower than the lighter one.
- The 15N bacteria was put into a broth of 14N and was replicated.
- Then it was spun in a centrifuge again and settled in between the 15N and 14N bands.
- From this, it can be concluded that DNA replication is semi-conservative as half of the DNA is the original and half is new, so would sit between them.
19
Q
What does ATP stand for?
A
Adenosine triphosphate
20
Q
Why is ATP needed?
A
Plants and animals don’t get enough energy from glucose directly, so it makes ATP, which is a nucleotide derivative to store energy.
21
Q
What is the structure of ATP?
A
It is made up of adenine (a nitrogen containing organic base), ribose (a pentose sugar) and a chain of 3 phosphates
22
Q
How is ATP used?
A
- energy is stored in bonds between phosphate groups, which is released by hydrolysis
- ATP diffuses to a part of the cell that needs energy to be used and the molecule breaks down into ADP (adenosine diphosphate) and Pi (inorganic phosphate)
- this reaction is catalysed by ATP hydrolase
23
Q
How is ATP used after the initial reaction for energy?
A
- ATP hydrolysis is coupled to other energy-requiring reactions so any leftover energy is used in these.
- the inorganic phosphate is stored to be used in another compound later, which increases this compound’s reactivity - this is called phosphorylation
- it can be resynthesised in a condensation reaction using ATP synthase enzyme
24
Q
Why is ATP resynthesised?
A
- photophosphorylation (in photosynthesis)
- oxidative phosphorylation (in respiration)
- substrate-level phosphorylation (phosphate groups transferred from donor molecules to ADP)
25
What is the role of ATP in organisms?
- immediate energy source (not long term due to instability)
- can be rapidly reformed into mitochondria
- used in metabolic processes
- used in movement
- used in secretion
- used in activation of molecules
26
Why is water important?
- good solvent for transport
- used in hydrolysis reactions
- maintains water potential
- controls temperature
27
What does the polarity of water mean?
Oxygen's unshared electrons give it a negative charge, which attracts it to hydrogen, which forms a positive charge. Therefore, weak hydrogen bonds are formed between the hydrogen atom of one water molecule and the oxygen of another.
28
What are the properties of water?
- surface tension
- cohesion (sticking to itself)
- solvent
- specific heat capacity
- latent heat of vaporisation
- condensation and hydrolysis reactions
29
Why is water a solvent?
Water is polar, which means that the negative oxygens attract positive ions and the positive hydrogens attracts negative ions, splitting ionic molecules apart.
30
How is water being a solvent useful?
- most biological reactions take place in a solution e.g. cytoplasm
- dissolved substances can be transported around the body e.g. in blood plasma
31
How is water useful with temperature?
- high specific heat capacity, due to many hydrogen bonds means water can absorb lots of energy before breaking so lots of energy is necessary to heat water
- water's high specific heat capacity makes it resistant to rapid temperature changes, so it acts as a temperature buffer to keep the body a stable temperature.
- high latent heat of vaporisation means lots of energy is needed to convert water from liquid to gas, therefore the evaporation of water can be used to cool the body without losing too much water
32
How is the cohesion of water useful?
- cohesion is the tendency for molecules to stick together, via hydrogen bonds
- adhesion is the tendency for molecules to stick to other materials
- both of these help water flow through organisms to carry substances throughout, even against gravity e.g. water transport in xylem
- cohesion causes high surface-tension when water meets the air, which is strong and stable
33
What is an inorganic ion?
It is an ion (atoms with a charge) that doesn't contain carbon
34
What is the role of iron (Fe2+)?
It binds to oxygen within haemoglobin in red blood cells
35
What is the role of phosphate ((PO4-)3-)?
It is a component of nucleotides and phospholipids and bonds store energy in ATP
36
What is the role of hydrogen (H+)?
It determines pH, affects protein shape and plays a part in chemiosmosis (ATP synthesis)
37
What is the role of sodium (Na+)?
It is used in the co-transport of molecules across membranes and is needed for generating nerve impulses and muscle contraction
38
What is the role of magnesium (Mg2+)?
It is a component of bones and chlorophyll, is required for energy production in ATP and maintains nerve and muscle function, as well as the immune system
39
What is the role of calcium (Ca2+)?
It regulates enzyme reactions and muscle contraction, releases insulin and glucagon from the pancreas and plays a part in nerve impulse transmission as it triggers synaptic vesicle exocytosis
40
What is the role of nitrates ((NO3)-)?
It makes nucleic acids and proteins and is a good source of nitrogen
41
What is the role of potassium (K+)?
It generates nerve impulses, used in muscle contraction and opens and closes the stomata to regulate fluid balance
42
What is the role of ammonium ((NH4)+)?
It regulates pH, removes nitrogenous waste and urea and is a good nitrogen source for plants
