Mcat: Dna

Front 1

Somatic Cells

Back 1

Includes a full complement of an organism's chromosomes.

Somatic = all cells other than gametes, spermatozoa, and ova.

Front 2

Human Somatic cell has # chromosomes?

Back 2

2n = 46

(diploid = 2n)

Front 3

Human Somatic Cell has # pairs of chromosomes?

Back 3

n = 23

Front 4

Hemizygous Pair

Back 4

One of the 23 pairs of chromosomes that constitutes the sex chromosomes.

Found in Males only.

Front 5

Female VS. Male sex chromosome terms

Back 5

Females = Homologous sex chromosomes (XX) (not autosomes)

Males = Hemizygous sex chromosomes (XY)

Front 6

All other chromosome pairs except the sex chromosome pair are termed?

Back 6

Homologous / Autosomes

Front 7

Prokaryote (bacterial) DNA

Back 7

Double Stranded
One highly coiled circular chromosome not enclosed in a membrane or nucleus.

Front 8

Structural arrangement of chromosomes and DNA in the Eukaryotic Cell

Back 8

Long, but fit because they are wrapped and coiled.

Wrap themselves around proteins called Histones.

Front 9

Histones

Back 9

Protein that allows for DNA to wrap around it so it can fit in the nucleus.

Near the time of cell division, the chromosomes wrap around their histones in a highly condensed form that makes the histones visible as discrete unites that resemble beads on a string.

Front 10

Visible units of histone are termed _______?

Back 10

Nucleosomes.
(occurs when chromosomes attach and wrap around the histone)

Front 11

Histones allow for?

Back 11

Proper reproduction of chromosomes.
In order for the chromosomes to physically fit within the nucleus and to undergo accurate reproduction, they must be packed efficiently.

Front 12

Histones are comprised of?

Back 12

Protein.
Histones are the protein component of the chromosome.

Front 13

Each DNA strand comprises a series of ____________ molecules bound together by _______________ bonds

Back 13

Each DNA strand comprises a series of deoxyribose molecules bound together by phosphodiester bonds.

Front 14

The backbone strands of DNA are made of alternating units of __________ and __________.

Back 14

The backbone strands of DNA are made of alternating units of deoxyribose and phosphate.

Known as the Sugar - Phosphate backbone.

Front 15

Base that is attached to the sugar and phosphate group is termed ?

Back 15

Nucleotides.

- Pairs of nitrogenous heterocyclic bases.

Front 16

4 different nitrogenous bases

2 groups

Back 16

Purines: Adenine and Guanine
Pyrimidines: Cytosine and Thymine

Front 17

Base pairing

Back 17

DNA strand backbone is made of alternating units of deoxyribose and phosphate.

A nitrogenous base (purine or pyrimidine) is bound to each deoxyribose-phosphate unit.

Purine pairs with Pyrimidine:
A + T
G + C

Front 18

Phosphodiester bonds exhibit what type of bonding?

Back 18

Covalent.

Not an example of dipole-dipole interactions.

Front 19

Are there hydrogen bonds in DNA?

Back 19

Hydrogen bonds function in holding nucleotide base pairs together but do NOT serve directly in the structure of the sugar-phosphate backbone.

However, due to their large number, they impart support to the DNA molecule. Just as they produce high surface tension for an aggregation of water molecules.

Not the same strength as covalent bonds though.

Front 20

Steric Hinderance and Base Pairing rules

Back 20

The rules of base pairing arise partly from steric hinderance, or size restrictions regarding the structure of the different bases and the spaces available to them.

Front 21

Structural difference between purines and pyrimidines?

Back 21

Purines: 2 rings
Pyrimidines: 1 ring

This is the reason why complementary bases across the rungs of the ladder must always have one of each for the backbone to be parallel.

Front 22

What would conceptually happen if a purine was base paired with another purine?

Back 22

The backbone of DNA would have to kink outwards to accommodate four rings.

Front 23

What would conceptually happen if a pyrimidine was base paired with another pyrimidine?

Back 23

The backbone of DNA would kink inwards.

Front 24

How many Hydrogen bonds are found in A + T?

Back 24

2 Hydrogen Bonds

Front 25

How many Hydrogen bonds are found in G + C?

Back 25

3 Hydrogen Bonds

Front 26

Define: DNA Variable region

Back 26

Portion of DNA molecule that presents it's unique sequence of nucleotides.

The DNA molecule's deoxyribose-phosphate component (the sides or backbone of the ladder) is not variable, however.

Front 27

Nucleosomes are functional units?

Back 27

No they are NOT!

They represent discrete packaging units within the chromosome.

Front 28

True facts about DNA double helix:

Back 28

1. Consists of two complementary strands.
2. Contains Deoxyribose - a sugar or carbohydrate.
3. Not composed of a phospholipid.

Front 29

What is the complementary strand of the DNA sequence:
5' - GCAAC - 3'

Back 29

3' - CGTTG - 5'

Front 30

The variable region of the DNA molecule carries:

Back 30

Nitrogenous Bases!
AKA Nucleotides!
AKA Purines and Pyrimidines!

Front 31

Orientation of Deoxyribose Strands?

Back 31

Antiparallelism of the deoxyribose sugars.
One strand runs in 5' -> 3'
the other strand runs 3' -> 5'

Front 32

Antiparallelism

Back 32

Refers to the orientations of the two sugar-phosphate backbones with respect to each other in a DNA molecule.

The 3' end of one strand is associated with the 5' end of the complement.

Front 33

When must a cell duplicate it's chromosomes?

Back 33

Prior to mitosis.
The replication of a chromosome requires the replication of DNA, which is called DNA synthesis, occurring at the S phase of the cell cycle.

Front 34

Where does DNA replication begin?

Back 34

At the Origin of Replication (Ori)
- a specific sequence of nucleotides that are the signal to start DNA synthesis.

Front 35

Helicase

Back 35

Enzyme that unwinds double stranded DNA.
Hydrogen bonds that join the base pairs rupture, and the two strands separate.

The deoxyribose-phosphate strands do not fully separate before daughter strands begin to form. They partially diverge at what is called a Replication Bubble which has two Replication Forks.

Front 36

Parent Strand

Back 36

Unwound strands of DNA prior to replication.
Serves as a Template for the production of a new daughter strand complementary to it.

This is accomplished by use of DNA polymerases which read the template strand and synthesize a new complementary daughter strand.

Front 37

DNA Polymerase

Back 37

DNA polymerases read the template strand and synthesize a new complementary daughter strand.
Requires a primer accomplished by Primase, which lays down short RNA primers so DNA polymerases can begin.

One-way enzymes.
Read: 3' -> 5'
Synthesize: 5' -> 3'

Front 38

Primase

Back 38

Just prior to DNA replication.
Lays down short RNA primers so DNA polymerases can begin.

Front 39

DNA Polymerase direction of action?

Back 39

One-way enzymes.

Read: 3' -> 5'
Synthesize: 5' -> 3'

Front 40

Why is the replicated DNA said to be Semiconservative?

Back 40

Each newly formed double helix contains only half the original DNA molecule.

Front 41

Direction of synthesis of top leading strand synthesis

Back 41

right to left, even though bubble is going from left to right.

Front 42

Okazaki Fragments

Back 42

Lagging strand.
The nucleotide chain production is called "Semidiscontinuous" synthesis, solves the polarity problem caused by the leading strand.

Front 43

Summarized DNA Replication

Back 43

1. Ori is recognized on the DNA strand.
2. DNA strands separate via helicase.
3. A replication bubble is formed with two replication forks.
4. RNA primers are laid down by primase.
5. DNA polymerases read the template strand 3->5 and synthesizes a new complementary strand 5->3.
*This can occer continuously (leading strand) or semidiscontinuously (lagging strand).
6. Okazaki fragments of the lagging strand are joined by DNA Ligase.
7. RNA primers are removed and replaced with DNA by DNA polymerases.

Front 44

DNA Polymerases catalyze:

Back 44

Addition of a nucleotide residue at the 3' end of a growing chain of nucleotide residues.

Front 45

The need for semidiscontinuous synthesis of one DNA daughter strand arises because of the:

Back 45

Antiparallel orientation of the two parent strands.

Front 46

With regard to DNA Replication, the term Template refers to the:

Back 46

Role of the parent strand in directing formation of a new complementary strand.

Front 47

Synthesis of a daughter DNA strand is facilitated most directly by:

Back 47

A polymerase enzyme

Front 48

With respect to chromosomal replication, a replication fork represents:

Back 48

Divergence of two parent strands, each of which then serves as a template for the creation of a new daughter strand.

Front 49

Okazaki fragments facilitate:

Back 49

Semidiscontinuous synthesis on the lagging strand.

Front 50

DNA when compared to RNA is:

Back 50

More stable
Permanent (RNA is Transient)
Double stranded (RNA is single)
Deoxyribose (vs. Ribose in RNA)