WEEK 2: CHROMOSOMES AND GENES Flashcards
What is DNA?
-DNA is heritable material that codes for all
proteins inside a cell.
What are introns and exons?
-Eukaryote cells’ DNA has genes with introns
( non coding) and exons (coding regions of DNA)
-In eukaryote cells, where is the DNA found?
-In eukaryote cells, DNA is found in the nucleus
and mitochondria (in the cytoplasm)
How much % of the DNA codes for functional genes?
About 2% of human DNA codes for functional
genes while the rest does not
What does DNA stands for?
-DNA stands for Deoxyribonucleic Acid
DNA is made up of three types of molecules.
Name them.
1)A five carbon sugar called deoxyribose
2)A phosphate group
3)A nitrogen containing base (4)
Name the 4 nitrogen containing bases that make up a DNA.
Adenine
Cytosine
Guanine
Thymine
DNA is built from Nucleotides.
What are these nucleotides called?
-DNA is built from Nucleotides
-These nucleotides are called deoxyribonucleoside triphosphates (dNTPs)
What base does dCTP contain?
a. Adenine
b. Guanine
c. Cytosine
d. Thymine
Name the four nucleotides.
The four nucleotides are:
a. deoxyadenosine triphosphate (dATP)
b. deoxythymidine triphosphate (dTTP)
c. deoxyguanosine triphosphate (dGTP)
d. deoxycytidine triphosphate (dCTP)
Which carbons do triphosphates and bases attach on the deoxyribose?
-The triphosphates are attached to deoxyribose at the 5’ carbon.
-The bases are attached to the 1’ carbon
Describe the joining of Nucleotides into a DNA Strand.
What two groups link on the nucleotides to form a DNA?
What is lost during the reaction?
-Nucleotides are joined together by linking a phosphate to the sugar on the adjacent nucleotide
-The phosphate group in one nucleotide (5’ Carbon) attaches the 3’Carbon (containing the hydroxyl group) in the deoxyribose of another nucleotide
-This process results in the loss of the other 2 phosphates, releasing energy
-Any nucleotide can be adjacent to any nucleotide
-The DNS strand can contain thousands and billions of nucleotides strung together
What is the 5’ end?
What is the 3’ end?
Cell build DNA strands (during replication) form what end?
-One end of the strand has phosphates at the 5’ carbon of the first nucleotide.
This is called the 5’ end.
-The other end has a hydroxyl group at the 3’ Carbon of the last nucleotide.
This is called the 3’ end.
-Our cells always build DNA strands (during replication) from the 5’ end to the 3’ end.
How does DNA form double strands?
Through base pairing
State the base pairing rule.
How many hydrogen bonds are in each pair?
Which bond pair is stronger?
*Base Pairing Rule
A always pairs with T
G always pairs with C
*This is accomplished via hydrogen bonds
A-T pair has 2 hydrogen bonds.
G-C pair has 3 hydrogen bonds.
*G-C bond > A-T bond
What is DNA double stranded structure called?
Describe the structure?
*Double helix
*The strands twist around one another in a right-handed double helix like in a spiral staircase.
*The bases are perpendicular to the helix axis
Describe the strand directionality.
Strand Directionality
*The two paired strands are antiparallel to
each other
*This means that one strands goes from 5’ end to the 3’ end while the other strand goes from 3’ end to the 5’ end.
What is DNA replication?
The process of DNA duplication.
State the need for DNA replication.
When does it occur?
Step 1: Replication Fork Formation
*This is performed by an enzyme known as DNA helicase.
DNA helicase disrupts the hydrogen bonding between base pairs to separate the strands into a Y shape known as the replication fork. This area will be the template for replication to begin.
Step 2: Primer Binding
*The leading strand is the simplest to replicate.
*Once the DNA strands have been separated, a short piece of RNA called a primer binds to the 3’ end of the strand.
*The primer always binds as the starting point for replication. Primers are generated by the enzyme DNA primase.
Step 3: Elongation
Enzymes known as DNA polymerases are responsible creating the new strand by a process called elongation.
*DNA polymerase I, II, IV and V are responsible for error checking and repair.
- DNA polymerase III binds to the strand at the site of the primer and begins adding new base pairs complementary to the strand during replication.
*Because replication proceeds in the 5’ to 3’ direction on the leading strand, the newly formed strand is continuous
*The lagging strand begins replication by binding with multiple primers.
- Each primer is only several bases apart.
-DNA polymerase then adds pieces of DNA, called Okazaki fragments, to the strand between primers.
-This process of replication is discontinuous as the newly created fragments are disjointed.
Step 4: Termination
*Once both the continuous and discontinuous strands are formed, an enzyme called exonuclease removes all RNA primers from the original strands.
*These primers are then replaced with appropriate bases.
*Another enzyme called DNA ligase joins Okazaki fragments together forming a single unified strand.
*The ends of the parent strands consist of repeated DNA sequences called telomeres.
Telomeres act as protective caps at the end of chromosomes to prevent nearby chromosomes from fusing.
A special type of DNA polymerase enzyme called telomerase catalyzes the synthesis of telomere sequences at the ends of the DNA.
*Once completed, the parent strand and its complementary DNA strand coils into the familiar double helix shape.
- In the end, replication produces two DNA molecules, each with one strand from the parent molecule and one new strand.
The replication fork is bi-directional.
Describe the leading strand and lagging strand.
However, the replication fork is bi-directional; one strand is oriented in the 3’ to 5’ direction (leading strand) while the other is oriented 5’ to 3’ (lagging strand).
What is a primer?
Primers are short RNA molecules that act as templates for the starting point of DNA replication.
How many DNA molecules are produced at the end after replcation.
- In the end, replication produces two DNA molecules, each with one strand from the parent molecule and one new strand.
What are telomeres?
What are their functions?
Name the enzyme that catalyzes the formation of telomeres.
*The ends of the parent strands consist of repeated DNA sequences called telomeres.
Telomeres act as protective caps at the end of chromosomes to prevent nearby chromosomes from fusing.
A special type of DNA polymerase enzyme called telomerase catalyzes the synthesis of telomere sequences at the ends of the DNA.
