DNA Flashcards
Draw the structure of a phosphodiester bond
What is the base paring for DNA?
adenine = thymine
guanine = cytosine
Why is DNA a stable molecule?
- the phosphodiester backbone protects the more chemically reactive organic bases inside the double helix
- hydrogen bonds link the organic base pairs forming bridges between the phosphodiester uprights
- because there are three hydrogen bonds between cysteine and guanine, the higher proportion of C—G pairings, the more stable the DNA molecule
How is DNA adapted to carry out its function?
- very stable structure. Rarely mutates
- two separate strands are joined only with hydrogen bonds, which allows them to separate during DNA replication and protein synthesis
- extremely large molecule and therefore carries an immense amount of genetic information
- by having base pairs within the helical cylinder of the deoxyribose-phosphate backbone, the genetic information is to some extent protected from being corrupted by outside chemical and physical forces
- Base pairing leads of DNA being able to replicate and to transfer information and mRNA
Name the two purine bases. How are they different from the pyrimidine bases? (name all the pyrimidine bases)
- The bases adenine and guanine are purines
– they have a double ring structure - The bases cytosine, thymine and uracil are pyrimidines
– they have a single ring structure
Which bases form two hydrogen bond?
adenine and thymine
What are the two requirements for semi-conservative replication?
- the four types of nucleotides (each with a different base) must be present
- a source of chemical energy to drive the process
Describe the process of semi-conservative replication?
- The enzyme DNA helicase breaks the hydrogen bonds between the two polynucloetide DNA strands causing the double helix to unzip, forming two single strands.
- Each original single strand then acts as a template for a new strand. Free-floating DNA nucleotides join to the exposed bases on each original template strand via complementary base pairing.
- The nucleotides of the new strands are joined together by the enzyme DNA polymerase, which catalyses a condensation reaction between the two adjacent nucleotides (joined together by phosphodiester bonds)
- This forms the sugar-phosphate backbone. Hydrogen bonds form between the bases on the original and new strand and the strands twist to reform the double helix.
What does semi-conservative replication of DNA ensure?
genetic continuity between generations of cells
Describe the anti-parallel nature of DNA
As the strands run in opposite directions (they are antiparallel), one is known as the 5’ to 3’ strand and the other is known as the 3’ to 5’ strand
Draw a dna polynucleotide
Describe the experiment that prove semi-conservation
Replicating Bacterial DNA in 2 types of Nitrogen Isotopes, 15N and 14N
Nitrogen found in nitrogenous bases of DNA
Bacterial DNA made from 15N will have a Heavy Density
Bacterial DNA made from 14N will have a Light Density
Experiment =
Sample of 14N and 15N in separate test tubes are centrifuged : 14 at top and 15 at bottom
Bacterial DNA made of 15N is extracted and is replicated in an environment of 14N – produces DNA molecules with half 15/half 14 (semi-conservative replication, original strand = 15N & new strand = 14N), therefore, DNA molecule has medium density
What are the components of ATP?
- Adenine
- ribose
- three phosphates group
Why is ATP easily broken?
the bonds between the phosphate groups are unstable = low activation energy = easily broken
The synthesis of ATP from ADP involves the addition of a phosphate molecule to ADP in three ways. What are these three ways?
- 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)
What is the chemical equation of ATP hydrolysis
