Chapter 5 CMB DNA Replication Flashcards
What is DNA?
- A double-stranded nucleic acid that contains the genetic information for cell growth, division and function.
- Made up of alphabets called bases (A,T,G,C*)
- These bases (arranged in triplets) code for amino acids which make up the proteins
Where are chromosomes located?
Located in the nucleus of eukaryotic cells
What are chromosomes composed of?
Composed of DNA wrapped around proteins called histones
What are chromosomes?
Physical carriers of genes
State the structural difference between chromatin and chromosome
Chromatin (decondensed or thread-like) vs chromosome (X-shaped: condensed chromatin)
What is a chromatin?
A complex of DNA and proteins in the nucleus, that condense to form chromosomes, in eukaryotic cell division
What are genes?
- Genes are basic physical and functional units of heredity.
- Genes are a set of instructions that determine what the organism is like, its appearance, how it survives, and how it behaves in its environment.
- Genes codes for a protein
- Genes codes for genetic traits that are inheritable
Are DNA and Genes same or different?
Functionally they are same, structurally they are different
What are Alleles and where are they located?
Alleles are 2 copies of a gene: One derived from the Mother and the other from the Father.
Located on homologous chromosomes
What is a locus? (Position)
Position of the allele on a chromosome
What are homologous chromosomes?
A pair of chromosomes, one inherited from each parent, that have corresponding gene sequences and that pair during meiosis.
What is a genome?
The complete set of genes in an organism
What is the structure of a DNA?
Double helix (twisted ladder)
Anti-parallel orientation
What is the structure of a right handed double helix?
Sugar phosphate backbone (upright) with bases attached to sugar and lie perpendicular to backbone
What is anti-parallel orientation of DNA?
- each sugar-phosphate chain runs in opposite direction
- A = T
- C = G
What are the 3 components of DNA?
- Bases (ATCG)
- Sugar
- Phosphate
How does DNA serve as the genetic basis for living things? RSVE
- Replication of information
- Storage of information
- Variation by Mutation
- Expression of information
What is storage of information?
Each somatic cell contains a complete set of chromosomes but expresses only part of the genetic information
(eg digestive cells only produce enzymes but not melanin)
What is variation of mutation?
Mutation: change in the A, T, G, C sequence of DNA
Beneficial (advantage passed on) vs Bad mutations (disorder & death)
What is expression of information?
DNA > transcription > mRNA -> translation > protein
What is the structure of a nitrogenous base?
Complex ring structures composed of Carbon and Nitrogen atoms
Name the 5 types of bases
Adenine, Thymine, Cytosine, Guanine & Uracil
What bases do DNA contain?
Adenine, Thymine, Cytosine & Guanine
What bases do RNA contain?
Adenine, Uracil, Cytosine & Guanine
What are purines composed of?
Adenine & Guanine
What are pyrimidines composed of? (Remember CUT)
Thymine, Uracil & Cytosine
How does A pair with T?
2 Hydrogen bonds
A === T
How does G pair with C?
3 Hydrogen bonds
G===_C
What is the ratio of purines and pyrimidines?
1 (same number of adenine and thymine molecules
same number of guanine and cytosine molecules)
State whether RNA & DNA is oxygenated
RNA: ribose (Oxygenated)
DNA: deoxyribose (Not oxygenated)
What is the function of phosphoric acid?
Connects adjacent sugars by a phosphodiester bond
What is DNA replication?
The process by which DNA makes a copy of itself
When does DNA replication occur?
Occurs during interphase, prior to cell division
What are involved in DNA replication?
dEET
- deoxyriboNucleosideTriPhosphate (dNTP)
- Energy source (ATP)
- Enzyme & proteins
- Template DNA
What does dNTP serve as?
Building blocks for DNA
State enzymes & proteins involved in DNA replication
1.DNA polymerases
2.Helicase
3.SSBP (Single-stranded DNA binding proteins)
4.Gyrase/Topoisomerase
5.Primase
6.Ligase.
What is template DNA for in DNA replication?
Parent base sequence that specifies the complementary sequence of the new daughter DNA
What are the 7 steps of DNA replication?
- DNA Gyrase:- unwinds the double helix
- DNA Helicase:- Unzips the double helix
- SSBP:- Stabilise the phosphodiester bonds between the sugar and phosphate preventing its breaking
- Primase:- Lays down RNA primer from which nucleotide polymerization can begin
- DNA Pol III:- Lays down complementary nucleotides in the 5’ – 3’ direction of the growing strand
- DNA Pol I:- Removes the RNA primers and lays down DNA nucleotides instead, however it leaves phosphodiester gaps towards the 3’ end.
- DNA Ligase:- Seals the gap in between the sugar-phosphate backbone (Okazaki fragments)
What is leading strand?
polymerase travels in the same direction as the helicase.
What is lagging strand?
moving away from the helicase
What are okazaki fragments joined together by?
Okazaki Fragments are joined together by DNA ligase
State the function of Gyrase/Topoisomerase in DNA replication
Topoisomerase/Gyrase creates nicks in DNA ahead of the replication fork to relax the supercoiling induced in the DNA by helicase activity
What is the junction between the unwound part and the open part in DNA replication called?
A replication fork.
Function of DNA helicase
-Breaks the hydrogen bonds between DNA strands
-Helicase unwinds and separates the DNA strands so that replication can continue.
Function of Topoisomerase
regulates over winding or under winding of DNA
Function of Single-stranded DNA binding proteins (SSBPs)
keeps the parental strands apart
Function of primase
synthesizes a RNA primer (beginning of new DNA strand synthesis)
Function of DNA polymerase I & III
DNA Polymerase III: Lays down complementary nucleotides in the 5’ – 3’ direction of the growing strand
DNA Polymerase I: Removes the RNA primers and lays down DNA nucleotides instead, however it leaves phosphodiester gaps towards the 3’ end.
Function of DNA ligase
covalently links the Okazaki fragments together. It plays a role in repairing single-strand breaks in DNA (basically fill gaps).
How are chromatids formed?
Result from the chromosome undergoing DNA replication just before cell division
Where will a chromatid be distributed in?
A daughter cell
What is a centromere and state its function.
Region with attachment sites for microtubules (spindle apparatus) that will move the chromosome during division
Why is RNA Primase required before DNA Polymerase is able to synthesize new strand?
-DNA polymerase can only add nucleotide but cannot initiate DNA replication.
-To initiate the DNA replication, the enzyme RNA Primase adds a short sequence called PRIMER to the “origin” region so that DNA replication can be started.
-DNA polymerase is now able to add nucleotide and continue the DNA replication
What can replication errors cause?
can cause a genetic MUTATION
How to prevent replication errors?
PROOFREADING by the polymerase prevents mismatches
DNA REPAIR ENZYMES can repair damaged DNA also
What are DNA binding proteins for?
keep the DNA apart
