Lecture 2 - DNA Structure and Dimensions and other (other: pg 13 - 23)

Question 1

DNA Structure and Dimensions:

1. The _____ double helix structure of
   DNA, correctly elucidated by James Watson and Francis Crick
2. ________ bases (A = T & C = G) are
   held together as a pair by ________ ________.

Answer 1

1. 3-dimensional
2. Complementary bases, hydrogen bonds

Question 2

Dimensions of DNA molecule

1. A single DNA molecule’s width is approximately ___ angstroms or 2 nm.
2. The length of one repeating nucleotide chain link (phosphate, sugar, base) is about _____
   Angstroms.
3. Around _____ nucleotide units are required to complete one full twist of the DNA helix
   which is 34 Angstroms

Answer 2

1. 20 Angstroms
2. 3.2 Angstroms
3. 10 nucleotide units

Question 3

Base pairing in DNA

1. ____ hydrogen bonds connect T to A; ___ hydrogen bonds connect G to C

The sugar-phosphate backbones run antiparallel to each other so that the ___’ and ___’ ends of the two strands are aligned.

Answer 3

1. 2 hydrogen bonds: T to A, 3 Hydrogen bonds: G to C
2. 3’ and 5’ ends of the two strands are aligned

Question 4

Nucleotides

1. The building blocks of nucleic acids are
   _______, which consists of a phosphate
   group, _______, and a nitrogen base
2. The _____ _____ connect the sugars to
   form two strands of nucleotides
3. _____ _______ between
   the nucleotides join the two nucleotide
   strands together. Adenine binds to thymine
   and cytosine binds to guanine
4. Deoxyribose carbon atoms are numbered.
   One end of a DNA strand has a 3’ end
   because of the ________ of its
   nucleotides. The other end of a DNA strand has a 5’ end.
5. The complementary strands are antiparallel
   in that the 5’ to 3’ direction of one strand
   runs _____ to the 5’ to 3’ direction of the other strand.
6. The nucleotide strands _____ to form a _______ helix.

Answer 4

1. nucleotides, consists of a phosphate group, sugar and a nitrogen base
2. Phosphate groups
3. Hydrogen bonds
4. orientation
5. counter
6. coil, double-stranded helix

Question 5

DNA and RNA assembly

DNA
1. ____ is assembled using deoxyribonucleotide triphosphates or _______ that include dATP,
dCTP, dGTP and dTTP.

2. When the deoxyribonucleotide triphosphate is inserted at the 3’ end of the growing DNA
   chain, the ________ is removed to give energy and only the deoxyribonucleotide monophosphate remains in the DNA backbone.

RNA
1. _______ is assembled using ribonucleotide triphosphates or ______ including ATP, CTP, GTP
and UTP.

2. When the _________ __________ is inserted at the 3’ end of the growing RNA
   chain, the diphosphate is removed to give energy and only the nucleotide ___________
   remains in the DNA backbone

Answer 5

DNA
1. DNA, dNTPS

2. diphosphate

RNA
1. RNA, NTPS

2. ribonucleotide triphosphate, nucleotide monophosphate

Question 6

Only one _____ ______ is inserted in DNA or RNA

Answer 6

phosphate group

Question 7

The pyrophosphate ________ is removed from the incoming dNTP and is recycled

Answer 7

(2PO4-)

Question 8

Nucleotides continued…

1. All nucleotides in RNA and DNA contain: _____
   ______ , _____________
2. DNA and RNA differ in the type of sugar, and in one base and both have a ____ carbon sugar.
3. DNA has ________ sugar and RNA has a _______ sugar.
4. _____ is the nitrogenous found only in RNA, and ______ is the nitrogenous base found only in DNA.
5. C, U, and T bases are _______ and G and A bases are ______.

Answer 8

1. In the order: 1) negatively charged phosphate group, 2) sugar, 3) A base (A, T, C, G –> DNA) or )(A, C, G, U –> in RNA)
2. both DNA and RNA have a5 carbon sugar
3. DNA sugar: Deoxyribose, RNA sugar: Ribose
4. Uracil: RNA, Thymine: DNA
5. C, U, T = Pyrimidines ; G, A = purines

Question 9

RNA molecule:

1. RNA is a _____________ molecule composed of nucleotides that contain the sugar _______ and the base _______ instead of thymine (which is found in _____).
2. There are many different types of RNA, but ___________ genes are transcribed into messenger RNA or ______ (aka to individual recipes for each protein chain).
3. mRNA’s are shorter than DNA because they are only ____ gene length

Answer 9

1. single-stranded, sugar: ribose, base: uracil, (thymine is only relative to DNA)
2. protein-encoding genes, transcribed into messenger RNA or mRNA
3. 1

Question 10

DNA and RNA

1. DNA is the _______ in individual cells and is present as long double-stranded molecules
   called chromosomes are visible.
2. Chromosomes are wrapped around nucleosomes to form ________.
3. RNA is single-stranded and is a copy of one of the DNA strands in a region that represents a ____ (we will discuss transcription of DNA to give RNA later)

Answer 10

1. template
2. Chromatin
3. Gene

Question 11

Differences between DNA and RNA:

Answer 11

DNA:
Sugar: Deoxyribose
Bases: A, C, T, G
Formation: in cells
Appearance: double-stranded,
Length: Usually chromosome length

RNA:
Sugar: ribose
Bases: A, C, U, G
Appearance: Usually single-stranded
Length: Usually single gene length

Question 12

The central Dogma (Francis Cricks idea)

1. DNA: __________ of DNA to give FNA by DNA polymerase.
2. ____________ of DNA to give RNA by RNA polymerase.
3. __________ of mRNA to give proteins by ________

Answer 12

1. replication
2. transcription
3. Translation, ribosomes

Question 13

Folding of DNA in Chromosomes – Nucleosomes

1. DNA is not usually _____
2. DNA is coated in ______ proteins so that both the DNA and protein make chromatin. These proteins are connected by ________ stretches of DNA.
3. The nucleosomes are coiled to form cylinders
   which are then coiled further several times to
   form the _____ that are visible in chromosomes

Answer 13

1. naked
2. histone, short stretches of DNA
3. fibres

Question 14

Chromosomes

1. In a replicated chromosome, each chromatid
   contains a double-stranded DNA molecule. The
   chromatids are joined at the ______.
2. A _________scanning micrograph showing several replicated human chromosomes.

Answer 14

1. centromere
2. colourized scanning micrograph

Question 15

DNA replication

1. During replication, the polynucleotide strands of a DNA molecule _____ and each serves as a template for the _____ of new strands.
2. This type of replication is called ____ _______ replication (discovered by Meselson-Stahl,1958).
3. After replication, each DNA molecule will contain 1 _____ polynucleotide strand and one ______ polynucleotide strand (gold).

Answer 15

1. separate and each serves as a template for the synthesis of new strands
2. semi-conservative replication
3. 1 old polynucleotide strand & 1 new polynucleotide strand

Question 16

The process of DNA repair

When DNA is damaged by ultraviolet light (1):

1. A section of one nucleotide chain is removed by a ______ enzyme (2) and the remaining chain (3) is used as a _______ by DNA polymerase to repair the DNA (4).
2. This type of repair works if there is one ____ strand of DNA that can be used as a
   template.

Answer 16

1. repair enzyme, template
2. intact