DNA Replication Flashcards
Nucleic Acids
Macromolecules that encode genetic material and direct gene expression
2 nucleic acids used by human cells
DNA and RNA
What are the monomers of nucleic acids?
Nucleotides
3 parts of nucleotides
Phosphate
Sugar
Base
Pentose sugar
Sugar used in DNA and RNA
Contains 5 carbons
Sugar used in DNA
Deoxyribose
Sugar used in RNA
Ribose
Difference between deoxyribose and ribose
Ribose has OH on carbon 2
Deoxy has H on carbon 2
Phosphodiester bond
C5 of each sugar bonds to phosphate molecule, and can react with OH group on C3 of another nucleotide sugar
What does a phosphodiester bond result in?
Sugar-phosphate backbone of DNA
4 DNA bases
Adenine
Thymine
Cytosine
Guanine
Primary Structure
Sequence of nucleotide bases in a single strand of nucleic acid
2 types bases can be divided into
Purines
Pyrimidines
Purines
Large bases
Contain 2 rings
Adenine and Guanine
Pyrimidines
Smaller bases
Contain only 1 ring
Thymine and cytosine
Complementary base pairing
Bases of 1 DNA strand bond to bases of another strand
Each base can only bond with its pairing
Purine must always bond to a Pyrimidine
Hydrogen bonds
Types of bonds formed between bases
Hydrogen atom of 1 base is attracted to nitrogen/oxygen atom of another base
Are hydrogen bonds stronger or weaker than ionic/covalent bonds?
Weaker (allows bonds to break with ease)
What bases form 2 hydrogen bonds
Adenine and thymine
What bases form 3 hydrogen bonds
Cytosine and guanine
What’s the secondary structure of DNA?
Complementary base pairing
Antiparallel
Sugar phosphate backbones face opposite directions
Is sugar phosphate backbone hydrophilic or hydrophobic?
Hydrophilic
Are bases hydrophobic or hydrophilic?
Hydrophobic
Minor groove
Smallest groove within helix of DNA
Occurs where overlapping backbones are closest together
Major groove
Occurs where gap btw backbones is greatest
Allows easy access for protein attachment
Supercoiling
DNA attaches to histone proteins and spools up DNA like fishing rod to keep it compact in nucleus
Chromatin
Combination of DNA and histone
What is the 4th structure of DNA
Chromatin
3 steps in DNA replication
Initiation
Elongation
Terminator
What does DNA replication require?
Pre existing DNA
Free nucleotides
Enzymes
Initiation and what does it involve
First step of DNA replication
Involves unwinding of double helix and breaking of hydrogen bonds
What does topoisomerase do?
Unwinds double helix of DNA exposing nucleotide bases making it easier for enzymes to attach
Helicase
Enzyme that breaks apart hydrogen bonds, separating the 2 strands
Where does helicase attach to?
Origins of replication once helicase has unzipped strands
Primers
Short sequence of RNA that serve as starting point for DNA synthesis
Elongation
Second stage in DNA replication
New DNA strands are synthesized
Semi conservative
Resulting DNA is a combination of parent strands and daughter strands
How do free nucleotides temporarily attach to open DNA strands?
Hydrogen Bonding
How does DNA polymerase synthesize daughter strands?
Fuses nucleotides together via sugar phosphate backbone
Replication fork
Opening in DNA behind helicase
Leading strand
Daughter strand in replication fork being synthesized in 5’ to 3’ direction
Lagging strand
Daughter strand in replication fork being synthesized in 3’ to 5’ direction
Okazaki fragments
Short sequences of lagging strand DNA
What enzyme is used to fuse Okazaki fragments together?
Ligase
What’s another job of DNA polymerase?
To proofread daughter strands as they are being produced
What happens if DNA polymerase fails to catch when a wrong nucleotide is added?
Mutation
Termination
Third and final stage in DNA replication
DNA copies are finalized and safe guarded from degradation
Termination sites
Found along parent strands
Direct helicase and DNA polymerase to detach
What do termination sites end in?
Replication fork
What occurs before last nucleotide in DNA strand?
Termination sites
What are the ends of chromosomes protected by?
Telomeres
Telomeres
Long sequences of DNA that protect chromosome from damage
What repeating sequence do human telomeres consist of?
TTAGGG
When do telomeres add the repeating TTAGGG sequence?
After final replication fork
What do telomeres lack?
The ability to code for proteins
Don’t contain any hereditary information
What happens when telomeres are used up due to excessive replications?
Genetic information is lost severely impacting organism health
What happens when telomeres are lost?
Chromosomes can no longer replicate
Can’t heal, grow or reproduce
Hayflick limit
Number of times DNA can replicate before using up all its telomeres
Senescence
Process of shortening your telomeres over time (cellular aging)
