Midterm 2 pt.3 Flashcards
Nucleotide?
5-carbons sugar bonded to a nitrogenous base and one or more phosphate groups.
Nucleic acid?
polymer consisting of many nucleotide monomers linked by a single phosphate group
Nucleoside?
nucleotide without any phosphate group
Structure of DNA?
deoxyribonucleic acid
Hydrogen on the second carbon(2’) of the ribose
Nitrogen bases are: Cytosine, Thymine, Adenine and Guanine
Structure of RNA?
ribonucleic acid:
Presence of an OH group on the second carbon (2’) of the ribose
Nitrogen bases are: Cytosine, Uracil, Adenine and Guanine
Polymerization only occurs…
Polymerization only occurs by the addition of nucleotides on the 3’
Sequences are always written from…
5’ to 3’
How is DNA oriented/ bonds?
2 polynucleotides: 2 strands organized in a double helix and oriented in opposite direction (antiparallel)
2 hydrogen bonds between A and T
3 hydrogen bonds between C and G
Replication is…
Replication is semi-conservative: Each new DNA molecule conserves half of the original molecule
What is the replication fork?
The 2 parental DNA strands are unwound by helicases.
Single-strand binding proteins maintain the strands separate.
A topoisomerase relieves the tension ahead of the fork.
What is the leading strand?
One strand can be synthesized continuously, in the same direction as the progression of the replication fork and using a single primer: leading strand
The DNA polymerase III synthesizes the new strand
elongation can only happen….
Elongation only happens in the 5’ 3’ direction!
what is the lagging strand?
One strand has to be synthesized in multiple segments, away from the replication fork, and using multiple primers: lagging strand
Fragments of the lagging strand are called Okazaki fragments
Once all primers have been replaced, a ligase binds the Okazaki fragments together into a continuous DNA stran
DNA- Dependant DNA Polymerase:
Synthesizes DNA
Uses DNA as a template to synthesize
RNA dependant DNA Polymerase
Synthsizes DNA
Uses RNA as a template to synthesize
Reverse transcriptase
New strand cDNA= complementary DNA
DNA-dependant RNA Polymerase
Synthesizes mRNA from DNA
RNA Dependant RNA Polymerase
Uses RNA to synthesize RN
What is the PCR? (3 steps)
Polymerase chain reaction: A cyclic reaction that makes a large number of copies of a small piece of DNA
1. Denaturation of parental DNA
2. Annealing of DNA primers
3. Extension
What is RT-PCR?
Reverse transcriptase–polymerase chain reaction
Technique for determining expression of a particular gene.
1. A reverse transcriptase to synthesize cDNA from an mRNA strand
2. A DNA-dependent DNA polymerase to copy the cDNA (PCR amplification by PCR)
What can cause DNA Damage?(5)
Oxygen radicals (O2*)
radiation
UV light
Chemotherapeutics
What are mismatch repairs?
Many DNA polymerases proofread each nucleotide added against its template.
Exonucleases remove the mismatched nucleotide that was just added
If the mismatched nucleotide is not removed, other enzymes remove it and replace it
mismatch repair mechanism performed by nucleases, polymerases and ligases
What happens when mutations occur?
When a DNA change carries through another round of replication it becomes a mutation:
If the mismatched nucleotide pair is replicated, it becomes permanent in the daughter cell.
In multicellular organisms, if the mutation occurs in germ cells it can be passed on to the next generation.
Most mutations have no phenotypic effect on the organism
What are telomeres?
repeated rounds of replication result in the shortening of chromosomes
But… the end of eukaryotic chromosomes DNA molecules have telomeres:
sequences of DNA (TTAGGG in humans) that can be repeated
Telomeres protect the organism’s genes from being eroded during successive rounds of replication
Telomerase?
Telomerase: enzyme that catalyzes the lengthening of telomeres in eukaryotic germ cells to compensate the shortening that occurs during replication.
The telomerase:
possess its own RNA “primer” molecule complementary to the end sequence of the DNA strand
