Nucleic Acids Flashcards
What are the monomers for DNA and RNA?
Nucleotides
What is the structure of a nucleotide?
- A phosphate group
- A pentose sugar (ribose/deoxyribose)
- Nitrogenous base (1 of 5 organic bases)
Which 4 nitrogenous bases does DNA contain?
- Adenine
- Thymine
- Guanine
- Cytosine
Which 4 nitrogenous bases does RNA contain?
- Adenine
- Uracil (replaces thymine)
- Cytosine
- Guanine
How many polynucleotide chains does DNA have?
2 anti-parallel polynucleotide chains
How many polynucleotide chains does RNA have?
1 polynucleotide chain
What protein is associated with DNA?
Histones
What is the function of DNA?
- Codes for proteins (amino acid sequences)
- DNA replication for cell division
What’s the function of RNA?
Transfers genetic information from DNA to ribosomes
What are pyrimidines?
They have a single ring structure
(Cytosine, Thymine Uracil)
What is a purine?
A two/double ring structure
(Adenine, Guanine)
What bond forms between neighbouring nucleotides?
Phosphodiester bonds form between a pentose sugar and phosphate group (in a condensation reaction)
What forms when many nucleotides are joined together (through phosphodiester bonds)?
Sugar-Phosphate backbone
What type of bond forms between complementary base pairs?
Hydrogen bonds
How many hydrogen bonds form between Adenine and Thymine (Uracil)?
2 hydrogen bonds
How many hydrogen bonds form between cytosine and guanine?
3 hydrogen bonds
Therefore More stable
What function does being a long and large molecule give DNA?
So it can store a lot of genetic information
What function does being a coiled helix give DNA?
So it’s compact
What function does having a sugar-phosphate backbone give DNA?
The bases in the double helix (middle) are protected
Why does DNA have bases arranged in specific sequences?
So it can code for specific amino acids
Why is DNA double stranded?
So it can be separated and unwound to act as a template for accurate replication using complementary base pairing
DNA has weak hydrogen bonds between the bases on each strand - how does this make it better for its function?
So the DNA helicase can easily be separated when it replicates
Which two enzymes are involved in DNA replication?
DNA Helicase
DNA Polymerase
Describe the process of DNA replication?
- The enzyme DNA helicase causes the DNA double helix to unwind and separate into two strands by breaking the hydrogen bonds between the complementary base pairs exposing the bases
- Both strands then act as a template for DNA replication
- Free activated DNA nucleotide (in the nucleoplasm) are attracted and hydrogen bond to complementary bases on the exposed templates strands by complementary base pairing
- The newly added nucleotides are then joined by DNA polymerase in a condensation reaction to form phosphodiester bonds between adjacent nucleotides
- This results in two identical FNA molecules being produced each of which contain one original DNA strand and one newly synthesised strand (Semi-Conservative)
What does DNA helicase do?
Unwinds and separates the double helix (by breaking the hydrogen bonds)
How is DNA replicated?
Semi-conservatively
Describe what is meant by semi-conservative replication?
The two identical DNA molecules produced contain one original DNA strand and one newly synthesised strand
What happens when the hydrogen bonds between the complementary base pairs are broken?
The base pairs on the strand are exposed to act as a template
What molecules are attracted and hydrogen bond to their complementary bases?
Free Activated DNA nucleotides
How do free activated DNA nucleotides bonds to the template strands?
They hydrogen bond to their complementary base pairs
Which enzyme joins the newly added nucleotides together?
DNA polymerase
What type of bond forms between adjacent nucleotides?
Phosphodiester bond (during condensation reaction)
How is chromatin formed?
DNA is wound around histone proteins
What is chromatin?
A more spread out form of DNA (which forms fibres)
What is a chromosome?
Most condensed form of DNA (formed from chromatin)
What are the two main stages of cell division?
Nuclear división (mitosis/meiosis) - nucleus divides
Cytokinesis - whole cell (cytoplasm) divides into daughter cells
What must happen before a nucleus can divide?
DNA replication
What’s a replication fork?
When DNA helicase and polymerase are working simultaneously so the bases aren’t exposed for too long
Why does DNA polymerase only add nucleotides in a 5’ to 3’ direction?
DNA polymerase has a complementary active site to the 3’ end
What were the 3 proposed DNA replication models?
- Conservative
- Dispersive
- Semi-conservative
What does the conservative model suggest about DNA replication?
One completely newly synthesised molecule is made and the original molecule is conserved
What does the dispersive model suggest about DNA replication ?
Fragments of DNA molecules are copied and dispersed in the structure
Which two scientist tried to validate Watson and Cricks model of semi-conservative replication ?
Meselson and Stahl
What three facts did Meselson and Stahl base their work on?
- All DNA contains nitrogen
- Nitrogen has an isotopes
- When bacteria grows in a medium they will absorb any nitrogen from the growth medium and incorporate it into any new DNA formed
What are the stages of Meselson and Stahl’s experiment?
- Bacteria are grown for several generations in a growth medium containing heavy nitrogen (N15)
- DNA is the extracted and spun in a centrifuge solution of caesium chloride. This forms a band near the bottom of the test tube
- The bacteria from the end of stage 1 is transferred and grown for 1 generation in a growth medium containing light nitrogen (N14)
- The DNA is extracted and spun in a centrifuge and a intermediate band is formed (due to one heavy and one light strand per DNA molecule)
- The bacteria from the end of stage 2 is grown for a second generation in the light nitrogen before the DNA is extracted and spun in a centrifuge (a light and intermediate band forms)
When spun in a centrifuge what happens to DNA?
Based on density/mass DNA will settle in the test tube
- Heaviest/most dense towards the bottom
- Lightest/least dense towards the top
At the end of the 5th stage of the experiment (DNA) why do we have one light and one intermediate strand?
2 DNA molecules are made from completely newly synthesised light nitrogen
2 DNA molecules have one light and one heavy strand
How can we disprove the conservative model?
After the first generation in the light nitrogen we would have seen one denser band and one less dense band but an intermediate strand was observed
How can we disprove the dispersive model for DNA replication ?
After the second generation in light nitrogen the band in the test tube would still be intermediate because there are still heavy DNA fragments in the molecule (although more light fragments have been joined/added)
