DNA Flashcards
Who discovered the structure of DNA?
Rosalind Franklin, but died before she could publish her results. Her results were them stolen by a Watson & Crick, who took the credit and earned a noble prize.
What is the structure of DNA?
DNA is a Double Helix:
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DNA is made up of nucleotides. What are the three components of nucleotides?
- A nitrogenous base
- A five-carbon sugar
- A phosphate backbone
What are the nitrogenous bases in DNA?
Adenine, Thymine, Guanine, and Cytosine (Note that these are also amino acids)
What are the nitrogenous bases in RNA?
Adenine, Uracil, Guanine, and Cytosine (Note that these are also amino acids)
What is Chargaff’s rule?
The nitrogenous bases are linked in base pairs of Adenine-Thymine/Uracil and Guanine-Cytosine. If this pattern does not follow, that is a genetic mutation.
What is point mutation?
A singular example of Chargaff’s rule being broken
What is the template strand and what is the complementary strand?
The template strand is the existing strand of DNA, and the complementary strand is the one that uses the template strand as a reference for its bases.
Are the amino acids in DNA acidic, basic, or neither?
Basic
Is it possible for uracil to mutate onto DNA/thymine to mutate onto RNA?
No, it’s one of the few truly impossible things in science
DNA replication is anti-parallel. What does it mean by anti-parallel?
DNA being anti-parallel means it’s parallel but moves in opposite directions of polarity, so one DNA strand moves in the 5’ to 3’ direction, while the other moves in the 3’ to 5’ direction.
How can you tell how many carbons there are in a carbon sugar?
You can count the corners, so a 5-carbon sugar had 5 carbons.
What is the main difference in the structure of RNA and DNA?
RNA is single-stranded, while DNA is double-stranded
What does RNA have that DNA doesn’t?
RNA has a 5 prime cap and a poly A (Adenine) tail, with no specific length.
What does DNA stand for?
Deoxyribonucleic Acid
What does RNA stand for?
Ribonucleic Acid
DNA strands are polynucleotides. What is a polynucleotide?
A polynucleotide is something made up of many individual units called nucleotides.
Where is the Nitrogenous base attached to the Five-carbon sugar
They are attached at the 1’ carbon of the sugar.
Where is the phosphate located in DNA?
Between the 5’ carbon of one sugar and the 3’ carbon of the neighboring nucleotide.
How are nucleotides attached to each other in DNA?
They attach to each other through phosphodiester bonds.
How are the nitrogenous bases in base pairs connected?
They are connected via hydrogen bonds.
Why do base pairs such as A-G or C-T not work?
They don’t work because the nitrogenous bases are not able to connect to each other strongly
What are pi-pi interactions?
pi-pi interactions form when the aromatic rings of the bases stack next to each other and share electron probabilities
The regularity of DNA’s structure causes two repeating and alternating spaces to form. What are they and what do they do?
They are called the major & minor grooves, and they can be used for base pair recognition and as a binding site for proteins.
DNA replication is semiconservative. What does that mean?
When DNA replicates, one strand is from an old DNA strand (the template strand) and one is newly synthesized (the complementary strand)
Match the nucleotides to their correct counterparts to make base pairs
5’ - G T C A C A G A T C T G A A - 3’
3’ - C A G T G T C T A G A C T T - 5’
DNA replication proceeds bi-directionally. what does that mean?
DNA replication occurs in both directions, with each strand going in a different direction
What does the helicase enzyme do?
The helicase enzyme separates the two DNA strands by breaking the hydrogen bonds that hold the base pairs together
When the DNA strands begin to separate, torsional strain is created. What enzyme solves this?
DNA gyrase solves this by reducing the torsional strain
What purpose do Single Stranded Binding Proteins (SSB Proteins) have?
SSB Proteins protect the separated stands from cleaving and stabilize the isolated strands in order to prevent them from sticking back together.
When the DNA is split up, what is the name of the newly split strands where DNA replication occurs?
The replication fork
What does DNA replication require to begin producing nucleotides?
DNA replication requires an RNA primer in order to begin, as it triggers DNA Polymerase III to begin making nucleotide strands.
What triggers DNA polymerase 3 and what does it do?
DNA polymerase is triggered once it sees the RNA primer, and it begins to synthesize a new strand in the direction that the DNA strand is being cut open, and does so in the opposite prime direction of the template strand. This strand is the leading strand.
What enzyme creates the RNA primer?
primease
When the leading strand begins making its nucleotide chain, what does the other strand do?
The other strand makes a primer that begins DNA polymerase in the direction opposite of the cutting, which is made in the opposite prime direction of their template strand. This strand is the lagging strand. As the replication fork is cut forward, more space is left behind the lagging strand, so another primer is placed, where DNA polymerase also starts. This repeats until the DNA strand is fully split
DNA replication is semi-discontinuous. what does that mean?
The leading strand makes nucleotides continuously, while the lagging strand makes them, then has to make another primer, making DNA replication semi-discontinuous.
When the RNA primers finish their job, what happens to them?
DNA polymerase 1 removes the RNA primers and replaces them with DNA material.
During DNA replication, there are spaces left between the lagging strands. What are they called and how are they fixed?
The spaces are known as Okazaki fragments and an enzyme known as DNA ligase seals the space between the primers
What part of DNA replication has exonuclease activity and what does it do?
DNA Polymerase 1 & 3 have exonuclease activity for the leading strand’s template strand and DNA Polymerase 1 also has exonuclease activity for the lagging strand. Exonuclease activity is done by an exonuclease enzyme that can remove incorrect nucleotides from a strand and replace them with the correct ones.
What does DNA Polymerase III do?
DNA polymerase III is activated by the RNA primers and makes nucleotide chains during DNA replication.
What does DNA Ligase do?
DNA ligase joins the sugar-phosphates of the Okazaki fragments in the lagging strand.
What does Primease do?
Primease makes the primers that begin the RNA chain from starch. Primease will be replaced by DNA material at the end of DNA replication.
What does Helicase do?
Helicase unwinds the double helix by breaking the hydrogen bonds that hold the base pairs together, creating the replication fork.
What does Topoisomerase do?
In the form of DNA gyrase, Topoisomerase relieves the DNA strand ahead of the replication fork in order to reduce the strain caused by the DNA strand splitting up.
Explain the steps of DNA replication
- The Helicase splits up the two DNA strands by breaking their hydrogen bonds
- Topoisomerase, in the form of DNA gyrase, relieves the DNA strand of stress due to it being split up.
- SSB proteins bind to the unzipped strands to keep them separated
- Primease adds primer on the DNA’s leading strand, and DNA Polymerase III adds nucleotide strands in the direction of the split
- A second primer is added to the other strand and DNA Polymerase makes nucleotide strands in the direction away from the split
- More primers are added to the lagging strand along with DNA polymerase to fill in the newly split parts.
- DNA polymerase I replace the primers with DNA material
- DNA ligase fills in the Okazaki fragments between the lagging strand’s primers
- An exonuclease enzyme checks for incorrect nucleotides and fixes them.