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SOM 201 > WEEK 2: CHROMOSOMES AND GENES > Flashcards

WEEK 2: CHROMOSOMES AND GENES Flashcards

1
Q

What is DNA?

A

-DNA is heritable material that codes for all
proteins inside a cell.

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2
Q

What are introns and exons?

A

-Eukaryote cells’ DNA has genes with introns
( non coding) and exons (coding regions of DNA)

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3
Q

-In eukaryote cells, where is the DNA found?

A

-In eukaryote cells, DNA is found in the nucleus
and mitochondria (in the cytoplasm)

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4
Q

How much % of the DNA codes for functional genes?

A

About 2% of human DNA codes for functional
genes while the rest does not

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5
Q

What does DNA stands for?

A

-DNA stands for Deoxyribonucleic Acid

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6
Q

DNA is made up of three types of molecules.

Name them.

A

1)A five carbon sugar called deoxyribose
2)A phosphate group
3)A nitrogen containing base (4)

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7
Q

Name the 4 nitrogen containing bases that make up a DNA.

A

Adenine
Cytosine
Guanine
Thymine

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8
Q

DNA is built from Nucleotides.
What are these nucleotides called?

A

-DNA is built from Nucleotides
-These nucleotides are called deoxyribonucleoside triphosphates (dNTPs)

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9
Q

What base does dCTP contain?

A

a. Adenine
b. Guanine
c. Cytosine
d. Thymine

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10
Q

Name the four nucleotides.

A

The four nucleotides are:
a. deoxyadenosine triphosphate (dATP)
b. deoxythymidine triphosphate (dTTP)
c. deoxyguanosine triphosphate (dGTP)
d. deoxycytidine triphosphate (dCTP)

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11
Q

Which carbons do triphosphates and bases attach on the deoxyribose?

A

-The triphosphates are attached to deoxyribose at the 5’ carbon.
-The bases are attached to the 1’ carbon

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12
Q

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?

A

-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

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13
Q

What is the 5’ end?
What is the 3’ end?
Cell build DNA strands (during replication) form what end?

A

-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.

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14
Q

How does DNA form double strands?

A

Through base pairing

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15
Q

State the base pairing rule.

How many hydrogen bonds are in each pair?

Which bond pair is stronger?

A

*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

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16
Q

What is DNA double stranded structure called?
Describe the structure?

A

*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

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17
Q

Describe the strand directionality.

A

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.

18
Q

What is DNA replication?

A

The process of DNA duplication.

19
Q

State the need for DNA replication.
When does it occur?

A
20
Q
A

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.
21
Q

The replication fork is bi-directional.
Describe the leading strand and lagging strand.

A

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).

22
Q

What is a primer?

A

Primers are short RNA molecules that act as templates for the starting point of DNA replication.

23
Q

How many DNA molecules are produced at the end after replcation.

A
  • In the end, replication produces two DNA molecules, each with one strand from the parent molecule and one new strand.
24
Q

What are telomeres?
What are their functions?
Name the enzyme that catalyzes the formation of telomeres.

A

*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.

25
Q

State the function of the following enzymes in DNA replication.

1.DNA helicase
2.DNA Primase
3.DNA Polymerases
4.Topoisomerase / DNA Gyrase
5.Exonucleases
6.DNA ligases

A

*DNA helicase - unwinds and separates double stranded DNA as it moves along the DNA. It forms the replication fork by breaking hydrogen bonds between nucleotide pairs in DNA.

*DNA primase - a type of RNA polymerase that generates RNA primers.

*DNA polymerases - synthesize new DNA molecules by adding nucleotides to leading and lagging DNA strands.

*Topoisomerase or DNA Gyrase - unwinds and rewinds DNA strands to prevent the DNA from becoming tangled or supercoiled.

*Exonucleases - group of enzymes that remove nucleotide bases from the end of a DNA chain.

*DNA ligase - joins DNA fragments together by forming phosphodiester bonds between nucleotides.

26
Q

How many base pairs does a human genome have?
How long is a DNA in one cell?
How long is the DNA in the whole body?

A

*Human genome = 3x10^9 base pairs

*A single haploid cell thus has 6x10^9 bp since a base pair is 0.34x10^-9meters, then 0.34x10^-9meters/bp x 6x109
bp=2.04m per cell

*Since there are about 50x1012 cells in the human body, then total DNA is about 100x10^12 meters long or 10^14meters long.

27
Q

If total DNA is about 10^14meters long, how is it
hidden away in the human body?

A

That much DNA must be packaged and compressed somehow in the cell.

28
Q

Describe the process of DNA packaging into a chromosome.

A

Step 1:

*Double stranded DNA helix forms a complex with nine protein molecules called histones (8 core histones plus H1 histone)
- Double stranded DNA is wrapped twice around the histones

Formed complex is called a Nucleosome.
A group of nucleosomes form DNA fibrils.

Step 2:
Groups of nucleosomes or DNA fibrils are supercoiled and packed together into 30nm chromatin fibers.

Step 3:
30nm chromatin fibers loops around to form loops that average 300nm in length. These uncondensed loops are bound to a protein scaffold.

Step 4: The 300nm chromatin fibers are compressed resulting in a 250nm wide and 700nm long chromatin fiber.

Step 5: The chromatin fiber is further compressed into
tight coils to produce chromatids of a chromosome.

29
Q

What are histones?
List all the histones.

A
  • They are rich in lysine and arginine residues, which give them positive charges that enable them to bind to the negatively charged DNA.
    *H1, H2A, H2B, H3, H4
    *8 core histones plus H1 histone
    *H2-H4 ARE CORE HISTONES, THEY ARE PAIRED.
30
Q

What are euchromatin and heterochromatin?

A

*Euchromatin is the part of the chromatin involved in the active transcription of DNA into mRNA.

-It is loosely bound nucleosomes and exposed DNA helical sequences that carry active genes accessible for transcription by polymerases and other regulatory protein complexes.

*Heterochromatin is a form of chromatin that is densely packed, it is condensed.

31
Q

What is a karyotype?

A

A karyotype is a diagram or photograph of chromosomes
in an organism.

32
Q

What information does a karyotype provide?
How are the chromosomes arranged?

A

A karyotype provides information on the number and
shapes of the chromosomes of an organism.

Can be used to identify :
- missing or additional chromosomes
- Chromosomal rearrangements or breaks

● Each chromosome is shown with its homologue
● Chromosomes are the stained and ordered by size
● Sex chromosomes are shown last even though they are
not the smallest

33
Q

Name the disorders.
1.Trisomy 21
2.Trisomy 18
3.XXY
4.XYY

A

Trisomy 21: Down Syndrome
Trisomy 18: Edward Syndrome
XXY Karyotype: Klinefelter Syndrome
XYY Karyotype: Jacob’s Syndrome

34
Q

Characteristics
● Hypogonadism
● Decrease in testiculat size from puberty
● Poor facial hair growth
● Educational difficulties are common

What disorder is this?

A

Klinefelter

35
Q

● Growth deficiencies
● Clenched hands with overlapping digits
● Cardiac defects
● Renal abnormalities

What disorder is this?

A

Edward’s syndrome

36
Q

State characteristics of Down Syndrome.

A

Characteristics
● Small hands and feet
● Flattened face
● Poor muscle tone
● Heart Defects

37
Q

State the abnormal numbers of sex chromosomes.

A

Abnormal numbers of sex chromosomes: Single X,
triple X chromosomes, double Y chromosome.

38
Q

What is trisomy?

A

Trisomy: Incorrect separation of chromosomes
during meiosis can lead to germ cells (usually ova)
with two homologous autosomes:- three copies of
an autosome.

39
Q

State the 4 types of genetic mutation.

A

*Deletion
*Duplicate
*Inverse
*Translocation

40
Q

How is a mitochondrial DNA inherited?

A

Carried by ovum and is inherited maternally.

41
Q

What can mutations in Mitochondrion genes lead to?

A

1) Liver Diseases
2) Hearing impairments
3) Visual Impairments
4) Cognitive Impairments

SOM 201 (29 decks)

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