Nucleic Acids & DNA Replication Flashcards
What are the important factors/functions of nucleic acids ?
-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 cells
What is a nucleic acid?
What is a nucleotide?
-Monomers/ building blocks of nucleic acids (DNA and RNA) both exist in all types of cells both carriers of genetic information
What does DNA stand for ?
Deoxyribonucleic Acid
What does RNA stand for ?
Ribonucleic Acid
What is the common structure of Nucleotides?
One to three phosphate groups which are linked by a phosphoester bond to a pentose (5-carbon atom) sugar, which in turn is linked to a nitrogenous base by a glycosidic bond
What is a phosphate group?
What is a phosphoester bond ?
What is a pentose sugar?
What is a nitrogenous base ?
What is a glycosidic bond?
What pentose sugar is found in a RNA nucleotide ?
Ribose
What pentose sugar is found in a DNA nucleotide?
Deoxyribose
Add nucleotide diagrams
What bases are present in DNA ?
Purines- Adenine and Guanine
Pyrimidines - Thimaine and Cytsine
What bases are present in RNA ?
Purines-Adeneine and Guanine
Pyrimines- Uracil and Cytosine
What are Pyrimidines ?
What are Purines?
Learn to read images of the nucleotides and be able to name them
What does RNA have that DNA does not when trying to figure out what the nucleotide is from an image?
RNA- Ribose at 2’ an OH group is connected
DNA does not have this hydroxy group
What is the function of nucleotides?
Forming nucleic acid polymers (DNA and RNA)
What is the function of nucleotides as a monomer?
-Biological energy carriers carrying high energy phosphate bonds (triphosphate nucleotides-ATP, GTP)
-To form coenzymes, essential for enzymatic activity
-Intracellular signalling molecules (Cyclic AMP or GTP)
What is a triphosphate nucleotide?
What does an Adenosine Triphosphate (ATP) nucleotide look like?
What does a Cyclic adenosine monophosphate (AMP) nucleotide look like?
How do nucleotides join together?
-Link covalently with each other by phosphodiester bonds and form a linear polynucleotide strand (polymers backbone)
-The phosphodiester bond links the 5’ end of one sugar with the OH group of 3’ end of the next
- Thus, nucleic acid strands have two ends. The directionality is 5’-3’ (e.g. 5’-ATGACGATC-3’)
- In prokaryotes (e.g bacteria) the 5’ and 3’ ends of DNA strands are linked to give circular DNA. This also applies for plasmids and mitochondrial DNA (eukaryotes)
What bond links the 5’ end of one sugar with the OH group of the 3’ end of the next nucleotide?
Phosphodiester bond
Two antiparallel polynucleotide strands of DNA can be held together by what bond?
H-bonds between complementary base pairs of double stranded nucleic acids
How are the complementary base pairs matched together?
- Two antiparallel polynucleotide strands of DNA can be held together by H-bonds between complementary base pairs of double stranded nucleic acids
1) A pairs with T (or U in RNA) through (2 H-bonds)
2) C pairs with G through (3 H-bonds, more stability as it requires more energy to break these 3 H bonds)
Why is there always a purine joined to a pyrimidine?
What is the DNA double helix?
The 2 DNA strands orientation is antiparallel, chains run in the opposite direction
-Its a 3D structure of DNA
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What are nitrogenous bases?
What is the sugar-phosphate backbone?
What is B form of DNA double helix?
-DNA in B form has helical grooves of different widths and accessibility
Major-wider
Minor-narrower
- B-type duplex is not possible for RNA, RNA is usually single-stranded
DNA can undergo reversible denaturation and renaturation.
What is DNA denaturation?
-DNA double strands can be separated into single strands through DNA DENATURATION, as H-bonds between complementary nucleotides can be broken, by increasing the temperature
-Higher temps are required to denature G-C pairs than A-T pairs due to its 3 hydrogen bonds
DNA can undergo reversible denaturation and renaturation.
What is DNA Renaturation ?
-When the conditions are reversed (DNA renaturation) -lowering the temperature - the hydrogen bonds between the complementary base pairs could be reformed to generate the double helix again.
What is the Mechanism for Heredity?
- Genome contains the genetic program that instructs a cell how to behave
- DNA provides biological messages thanks to precise sequence of their nucleotides
- The ‘alphabet’ of DNA is composed of 4-letter nucleotides (A, C, T, G)
What is a gene?
- Unit of heredity. Human genome has approx 25,000 genes(<1.5% of DNA)
- Genes contain instructions for producing specific proteins (DNA-RNA-PROTEINS)
- The nucleotides sequence of a gene encoding the amino acids sequence of a protein (genetic code)
What is a unit of heredity?
-A gene
Where is DNA found in eukaryotic cells?
-In the nucleus (nuclear DNA)
-In the mitochondria (mitochondrial DNA)
What is Nuclear DNA. ?
- DNA molecules are packaged with histones into chromatin
- Nucleosomes = chromatin units
What are Nucleosomes?
In dividing cells, chromatin is further condensed into what?
Chromosomes
- (series of coils and loops) Formed in Prophase of mitosis (X shape chromosomes because of the duplicated DNA)
- Number, size, shape of chromosomes is species-specific (Karyotype)
What is Chromatin?
What is a chromosome?
How many PAIRS of chromosomes do human cells have?
22 pairs of homologous autosomal chromosomes + 2 sex chromosomes
What are Gametes ? and how many chromosomes do they have?
-Sex cells (sperm and eggs) - Haploid cells
-These have one set of 23 chromosomes
-A set of 23 chromosomes is received from the mothers gamete and a set of 23 via fathers gamete
What are haploid cells ?
What are homologous cells?
What is a Karyotype?
What is DNA replication?
- DNA replication is the process by which DNA makes a copy of itself
- Before a cell can divide (Mitosis), its DNA (chromosomes) needs to be copied/ to obtain two two genetically identical daughter cells
- Occurs in the nucleus during Interphase (Phase S synthesis)
- During cell division, each of the 46 chromosomes contains two identical duplicated DNA molecules (two sister chromatids joined at the centrometre)
- DNA must rapidly and accurately copy(replicate) its nucleotide sequence in order to avoid mistakes, mutations
How does a cell divide?
-Through Mitosis
How does DNA make a copy of itself?
-Through the process of DNA replication
Where does DNA replication occur?
-In the nucleus during Interphase
What are sister chromatids?
What is the Centrometre?
DNA must rapidly and accurately copy(replicate) its nucleotide sequence in order to avoid mistakes, mutations such as what?
-Risk of diseases in human cells e.g cancer
-Development of drug resistance in viruses or bacteria
What is the DNA replication -Semi conservative process?
It produces two copies of DNA, each that contains one original strand and the one new strand
- DNA replication consists of 4 steps
How many steps does DNA replication consist of and what are they?
4 steps
1) Replication Fork Formation
2) Initiation
3) Polymerase elongation
4) Termination
What is Fork Formation?
- DNA replication starts at a sequence (rich in A-T pairs) called origins (thousands/genome)
- Double helix is opened by initiator proteins
- At each origin, helicases proceed bidirectionally to unwind/unzip the DNA double strands, creating two Y-shaped junctions called replication forks.
- Bidirectional DNA replication
(initial breakage of H bond, these attract helicases, in 2 point of the replication origin, move away in opposite directions)
What is Initiation in terms of DNA replication ?
- DNA polymerase needs a short RNA primer (produced by (enzyme, DNA primase) to start(free 3’ -OH end)
- DNA polymerase allows the incorporation of nucleotides to the 3’ end of a growing DNA strand, using one parental DNA strand as a template
- It requires nucleotide triphosphates (high-energy phosphate bonds fuel the reaction)
- New DNA strands are synthesised from 5’ to 3’ (5 prime to 3 prime)
- 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 is the replication fork?
Asymmetrical
What are the 3 key players of DNA replication?
-DNA Polymerase
-DNA Helicase
-DNA Ligase
What is DNA polymerase?
-Group/complex of polymerases
-Incorporates nucleotides to the growing DNA strands by forming phosphodiester bonds
-One nucleotide at a time (triphosphate form)
main function of DNA polymerase - adding nucleotides to the new DNA strands during replication
What is DNA Helicase?
-Unwinds parental double helix
What is DNA Ligase?
-Joins Okazaki fragments and seals other breaks in sugar-phosphate backbone
What is the main function of DNA polymerase?
Adding nucleotides to the new DNA strand during replication
