W3 Nucleic Acids & DNA Replication Flashcards
Dr Nannetti
Which of the following related to nucleic acids are correct?
- They are carriers of genetic information
- They are made of nucleotides
- They are represented by DNA and RNA
- They are present in every type of cell
All of the above
Structure of a nucleotide
Pentose sugar
Nitrogenous base
Phosphate group (1-3)
What bond is between a phosphate group and pentose sugar?
Phosphodiester bond (Phosphoester)
What bond is between a pentose sugar and nitrogenous base?
Glycosidic bond
What are the bases in RNA?
Adenine, Cytosine, Guanine, URACIL
What is a nucleoside?
The part of a nucleotide consisting of only the pentose sugar and nitrogenous base (not phosphate)
How can DNA and RNA be distinguished?
(not by base which is easier)
DNA (DEOXYribose) has a H at 2’ whereas RNA (ribose) has an OH at 2’
(deoxy- no oxygen)
And also,Thymine for DNA and Uracil for RNA
What bases are pyrimidines?
(hint-pyramid)
Cytosine, Thymine, Uracil
Which bases are purines?
Adenine, Guanine
Differences between purines and pyrimidines?
Purines are double ring (shorter name=longer)
Pyrimidines are single ring
What is the corresponding nucleoside for base Adenine in DNA and RNA?
(nomenclature)
RNA- Adenosine
DNA- Deoxyadenosine
What are the functions of nucleotides? (3)
- Biological energy carriers (ATP, GTP)
- To form coenzymes
- Intracellular signalling molecules
How can nucleotides link?
Nucleotides can link covalently with each other by phosphodiester bonds and form a polynucleotide strand.
(in condensation reactions)
Where is the phosphodiester bond? which C?
The phosphodiester bond links the 5’ end of one sugar with the OH group of the 3’ end of the next.
Thus nucleic acid strands have two ends. The direction is 5’ to 3’
How do DNA strands link in prokaryotes?
In prokaryotes, the 5’ and 3’ ends of the DNA strands are linked to give circular DNA. This applies for plasmids and mitochondrial DNA (eukaryotes)
What is the DNA double helix structure?
2 anti parallel strands
Sugar Phosphate backbone
DNA bases facing inwards (complementary base pairs)
What is DNA reversible denaturation?
DNA double strands can be separated into SINGLE strands by breaking the temporary H bonds (upon heating)
What is DNA reversible renaturation?
Renaturation: temp lowered to generate double helix again
What is the genome?
It contains the genetic program that instructs a cell how to behave?
Where is DNA located in eukaryotes?
Mostly in the nucleus (packaged with histones into chromatin)
What is chromatin formed of?
Formed of nucleosomes.
Half DNA and half protein
How many pairs of chromosomes do humans have?
22 pairs of chromosomes and 2 sex chromosomes
What is DNA replication?
DNA Replication is the process by which DNA makes a copy of itself
Mitosis occurs in the nucleus during interphase.
What are the 4 steps of DNA replication?
- Replication fork formation
- Initiation
- Polymerase elongation
- Termination
What is produced in DNA replication?
Two copies of DNA are produced. Containing one original and one new strand.
What happens in Replication Fork Formation?
- DNA polymerase needs a short RNA primer (produced by DNA primase) to start (free 3’ -OH)
- DNA polymerase allows the incorporation of nucleotides to 3’ end of a growing DNA strand, using one parental DNA strand as a template.
- It requires nucleotide
- New DNA strands are synthesised from 5’ to 3’
- It forms a phosphodiester bond between the 3’ end of the growing DNA chain and the 5’ phosphate group of the incoming nucleotide (esterification)
What happens during Initiation?
- DNA polymerase needs a short RNA primer (produced by DNA primase) to start (free 3’ -OH)
- DNA polymerase allows the incorporation of nucleotides to 3’ end of a growing DNA strand, using one parental DNA strand as a template.
- It requires nucleotide
- New DNA strands are synthesised from 5’ to 3’
- It forms a phosphodiester bond between the 3’ end of the growing DNA chain and the 5’ phosphate group of the incoming nucleotide (esterification)
What happens during termination?
- Because the parental strands are antiparallel, the replication fork is asymmetrical.
- Replication of the leading strand is continuous
- Replication of the lagging strand is discontinuous (opposite direction from the fork movement)
- It requires many RNA primers
- Synthesis of small DNA fragment
- RNA primers are degraded and replaced by DNA chain growth from the previous Okazaki fragments
The enzyme DNA ligase joins adjacent fragments (phosphodiester linkage between DNA stretches)
Which enzyme proofreads during DNA replication?
DNA polymerase does, making DNA synthesis an accurate process.
What does polymerase do?
Incorporates nucleotides to the growing DNA strand
What does helicase do?
It unwinds the parental double helix
What does ligase do?
It joins Okazaki fragments and seals breaks in sugar phosphate backbone