DNA Flashcards
What is the monomer of nucleic acid?
Nucleotide
Where is located nucleic acid in the eukaryotes?
In the nucleus, organelles
Where is located the nucleic acid in prokaryotes?
Not enclosed in a membranous enveloppe
How DNA forms chromatin?
Forms a complex with histone proteins
How does DNA controls all the cellular activity?
By turning «on» and «off» genes
Of what nucleotides are made?
-nitrogenous base
-pentose sugar
-phosphate group
What is DNA backbone?
Sugar and phosphate lying on the outside of the helix
Helix strands run it what direction?
Opposite
What is anti parallel orientation?
5’ carbon end of one strand will face 3’ carbon end of its matching strand
What is the basic of base complementary rule?
A pairs with T
G pairs with C
How many base pairs are present per turn of the helix?
10
How pairs binds to each others?
By hydrogen bonds
What is the major difference between RNA and DNA?
-RNA is single-stranded
-mostly involved in protein synthesis
-Less stable than DNA
-Ribose sugar
-Involved in gene expression
How ribonucleotides are linked?
By phosphodiester bonds
What is the pentose sugar used in RNA?
Ribose
Which base is absent in RNA that is present in DNA?
T replaced by U
RNA based sequence is complementary to what?
DNA’s coding sequence from which it has been copied
What is the function of mRNA?
Read in sets of three bases (codons)
*each codons codes for a specific amino acid
What is the function of rRNA?
-Ensure proper alignment of the mRNA and the ribosomes
-Catalyse peptide bond formation between two aligned amino acids
What are examples of purines?
-Adenine (A)
-Guanine (G)
What are examples of pyrimidine?
-Cytosine (C)
-Thymine (T)
What is a nucleoside?
A base attached to a five-carbon sugar
How many hydrogen bonds are between adenine and thymine?
2 hydrogen bonds
How many hydrogen bonds are between cytosine and guanine?
3 hydrogen bonds
Why DNA is negatively charged?
Because of its phosphate group
What contains heterochromatins?
Genes not expressed — found in the centromere and telomeres
What is the packing DNA strategy in Prokaryotes?
Supercoilling
In DNA synthesis, how phosphodiester bond are formed?
By déshydratation synthesis
What is the role of DNA polymerase?
Adds nucleotides one-by-one to the growing DNA chain
What happens when the bonds between phosphate are broken?
Energy is released — use to form phosphodiester bonds between the incoming nucleotide and the growing chain
What is the function of DNA pol I?
Replaces RNA primer with DNA
What is the function of DNA pol II?
Repairs mis-matched bases
What is the function of DNA pol III?
Adds nucleotides in the 5’ to 3’ direction
In prokaryoties does it have multiple origin of replication?
No
What is the function of helicase?
To unwind the DNA by breaking the hydrogen bonds between nitrogenous base pairs
What is require for the process of replication?
ATP hydrolysis
What is the replication forks?
Y-shaped structures that forms when DNA opens up — get extend bi-directionally as replications proceeeds
Where are located replisome?
In the middle of each replication forks
What is the function of replisome?
To unzips old DNA and synthesize new DNA
What is the function of single-strand binding proteins?
-Coat the single strands of DNA near the replication fork to prevent the single-stranded DNA from winding back into a double helix
-Protects the hydrophobic base from exposure to water
What is the major restrictions for DNA polymerase?
-only able to add nucleotides in the 5’ to 3’ direction
What is the function of the primer?
Provides freee 3’-OH end so it can create a phosphodiester bond with the 5’ phosphate of the next nucleotide
What is the function of RNA primase?
-Synthesizes an RNA segment that is about 5 to 10 nucleotides and complementary to the template DNA
-make RNA primer for DNA pol III to stick onto
What is the function of topoisomerase?
Counteracts the helicase rotation
What is special about the lagging strand?
Contains Okazaki fragments
What is the specificity of the Okazaki fragments?
Require new primer for each of the short fragments to start synthesizes
What is the direction of the lagging strand?
3’ to 5’
What is the function of ligase?
Seals the gap between Okazaki fragments to create one continuous DNA strand
*catalyses the formation of phosphodiester linkage
Enumerate the 10 main steps of DNA replication
1-DNA unwinds at the origin of replication
2-Helicase opens up the DNA forming replication forks
3-Single strand biding protein coat the DNA around the replication fork
4-Topoisomerase binds at the region ahead of the replication fork
5-Primase synthesize RNA primers complementary to the DNA
6-DNA pol III starts adding nucleotides to the 3’-OH end
7-Elongation of both lagging and leading strand
8-RNA primers are removed
9-Gaps are filled by DNA pol I adding dNTP’s
10-Gaps between the two fragments is sealed by ligase
What is the main difference between Eukaryotic and Prokaryotic replication?
Eukaryotic =
*more complicated and slower
*different polymerase enzymes
*multiples origins of replication
*linear chromosomes
What opens the DNA helix?
Helicase that uses ATP hydrolysis
What is the function of the sliding clamp protein?
Holds the DNA pol in place so that it does not slide off the DNA
What is the problem that the lagging strand encounters in eukaryotes replication?
When the end of the chromosome is reached there is no way to replace the primer on the 5’ end
What is telomeres?
Comprise repetitive sequence that code for no particular gene
*Can be added to the ends of chromosomes
What is the function of telomerase enzyme?
Attaches telomeres to the end of the chromosomes so the DNA polymerase can add nucleotides complementary to the ends of chromosomes
Telomere shorting is associated with what?
Aging
What is the function of telomerase?
Extends the leading strand at telomere with DNA using RNA primer as a template for reverse transcription
What explains that chromosomes gets shorter with each cell division when aging?
Because telomerase becomes less active in adults
How SANGER sequencing is based DNA replication?
Since it uses template, primer, DNA polymerase and Chain termination
**Uses ddNTPs (lack 3’-OH)
What is the ultimate goal of PCR?
Amplify specific DNA regions
How DNA replication is the basis for PCR techniques?
Since it also requires a DNA polymerase enzyme that makes new strands of DNA
