Nucleic Acids, DNA & ATP Flashcards
What are nucleotides?
Monomers that are the building blocks of DNA.
What is the basic structure of a nucleotide?
- ribose sugar (joined to…)
- phosphate group
- nitrogenous base
What are the 5 different bases?
- Guanine (G)
- Thymine (in DNA) / Uracil (in RNA) (T)
- Adenine (A)
- Cytosine (C)
What are purines?
Larger bases with double rings of C and N - cytosine, thymine / uracil.
What are pyrimidines?
Smaller bases with single rings of C and N - adenine, guanine.
What are DNA and RNA both examples of?
Nucleic acids
- DNA is deoxyribonucleic acid as it’s ribose sugar is dexoyribose.
- RNA is ribonucleic acid as it’s ribose sugar is ribose.
What are DNA and RNA?
They are both long chain polymers made up of many individual nucleotides.
What are the main other differences between DNA and RNA?
- DNA is a double stranded molecule, RNA is single stranded
- DNA has hydrogen bonding, RNA does not
- DNA has a complementary base pairing, RNA does not
How are DNA and RNA chemically different?
Deoxyribose sugar has one less oxygen than ribose sugar. It has a H atom attached to it, where ribose sugar has a hydroxyl (OH).
How do nucleotides join?
Nucleotides join via a condensation reaction to form a phosphodiester bond. They are attached between the sugar of one nucleotide and the phosphate of another.
The chain of sugars and phosphates is known as the sugar-phosphate backbone.
How are polynucleotides broken back down?
They are broken back into nucleotides by breaking the phosphodiester bonds in a hydrolysis reaction.
How does a DNA molecule’s double helix work?
The two strands of the double helix are held together by hydrogen bonds between the bases. Each strand has a phosphate group at one end and a hydroxyl group at the other.
They are arranged so they run in opposite directions and are said to be “antiparallel”.
What are the complementary base pairings in DNA?
Adenine and Thymine / Uracil
Cytosine and Guanine
Why does adenine form a complementary base pairing with thymine / uracil?
They are both able to form two hydrogen bonds.
Why does cytosine form a complementary base pairing with guanine?
They are both able to form three hydrogen bonds.
What do complementary base pairings mean?
DNA always has equal amounts of adenine + thymine, and cytosine + guanine.
Small pyrimidine bases always bind to larger purine bases, resulting in parallel polynucleotide chains.
How does the structure of DNA relate to it’s function?
- sugar-phosphate backbone - DNA is strong and stable
- many hydrogen bonds - provides strength and stability
- weak hydrogen bonds - strands can be separated during DNA replication
- double stranded - bases are protected and replication can be semi-conservative
- long polymer - can store lots of genetic information
- double helix - compact
- bases in sequence - allows accurate DNA replication
What is DNA replication?
DNA copies itself before cell division so that each new cell has the full amount of DNA.
Why is DNA replication important?
- making new cells for growth and repair
- passing on important between generations (reproduction)
- DNA replicate must be an exact copy to form two sister chromatids
What does DNA helicase do?
DNA helicase attaches to the DNA molecule and causes the hydrogen bonds between complementary bases to break. This separates two polynucleotides.
How does a new DNA strand form?
Free activated nucleotides line up with their complimentary bases on the DNA. They are only held in place by hydrogen bonds and not by phosphodiester bonds.
Why are free nucleotides “activated”?
They contain three phosphates as opposed to one.
What does DNA polymerase do?
DNA polymerase moves down the strand, catalysing the formation of phosphodiester bonds between activated nucleotides.
The extra two phosphate groups leave the nucleotides to provide energy for the reaction.
What is meant by semi-conservative replication?
The new DNA strand contains one original strand and one new strand.
What happens when copying is incorrect?
Incorrect copying can be random and spontaneous, which can lead to genetic mutations.
What is ATP?
Adenosine Triphosphate
What is the structure of ATP?
- ribose sugar
- nitrogenous base adenine
- 3 phosphate groups
This makes ATP a nucleotide
What does ATP do?
It allows for energy from glucose to be transferred in smaller, more useful amounts.
Why are ATP molecules useful for transferring energy?
A very small amount of energy is needed to break the covalent bonds between the phosphate groups, but they release a large amount of energy.
This is a hydrolysis reaction.
What is the reaction for the hydrolysis of ATP?
ATP + water –> ADP + Pi + energy
What is ADP?
Adenosine Diphosphate
What does the “i” mean in the phosphate group?
It means the phosphate group is inorganic as it does not contain carbon.
What enzyme catalyses ATP hydrolysis?
ATPase / ATP hydrolase
What is ATP needed for?
- active transport
- muscle contraction
- forming larger molecules in anabolic reactions
What is meant by phosphorylated reaction?
ADP and the phosphate are recycled back to ATP during respiration and photosynthesis.
It is a condensation reaction catalysed by ATP synthase.
What are the three key parts of DNA purification?
- breaking (lysing) the cells and disrupting the nuclear membranes to release the DNA
- using enzymes to denature and remove associated proteins
- precipitating the DNA using an organic solvent
Describe the process of DNA purification (1):
- Place ethanol in a freezer 24 hours before starting - must be ice cold.
- Cut onion into small pieces (5mm x 5mm).
- Add 10cm3 washing up liquid to 90cm3 tap water in a beaker. Add some of the onion pieces.
- Place water in a 60°C water bath for 15 minutes.
- Cool mixture in ice water bath for 5 mins and stir continually - important in preventing breakdown of DNA. Constant stirring ensures the whole mixture has cooled.
Why does the sample need to be placed in a 60°C water bath?
The detergent and heat disrupt the cellular membranes’ phospholipid bilayer - DNA is released.
The heat also denatures enzymes released by the cell.
Describe the process of DNA purification (2):
- Blend mixture for 5 seconds - further breakdown of membranes but does not break DNA.
- Use filter paper to filter into another beaker - removes cell debris and membrane fragments. The filtrate contains DNA and associated proteins.
- Pour 10cm3 into a test tube and add protease - denatures and removes proteins.
- Add ice cold ethanol and wait 2-3 minutes - nucleic acids insoluble in ethanol so DNA forms a precipitate at the top of the mixture.
