CHAPTER 9: DNA & the Molecular Structure of Chromosomes

a) 20% of bases are C, what percentage of the bases are A? b) How about if 37% of the bases were C, what is the new A?

a) 30% b) 13 %

Double stranded DNA contains 200,000 base pairs. How many: a) nucleotides? b) complete spirals on each strand? c) present atoms of Phosphorus? d) what is the length of the DNA?

a) 400,000 - multiply base pairs by 2 b) 20,000 - 10 base pairs per turn c) 400,000 - one phosphorus per nucleotide d) 68,000 nm - 2.94 (?)

What is the physical nature of each strand of DNA? a) 35% A, 35%T, 15%G, 15%C b) 35%A, 15%T, 25%G, 25%C c) 35%A, 30%U, 30%G, 5%C

a) Double-stranded DNA b) Single-stranded DNA c) Single-stranded RNA

Indicate whether each statement is true or false: a) A+T=G+C b) A=G; C=T c) A/T=C/G d) T/A=C/G e) A+G=C+T f) G/C=1 g) A=T within each single strand h) H-Bonding provides stability to the double helix in aqueous cytoplasms i) Hydrophobic bonding provides stability to the double helix in aqueous cytoplasms j) When seperated, the two strands of a double helix are identical k) Once the base sequence of one strand of a DNA double helix is known, the base sequence of the strand can be deduced l) The structure of a DNA double helix is invariant m) Each nucleotide pair contains two phosphate groups, two deoxyribose molecules, and two bases

a) FALSE b) FALSE c) TRUE d) TRUE e) TRUE f) TRUE g) FALSE (true within each double strand) h) TRUE i) TRUE j) FALSE k) TRUE l) FALSE (A,Z,B) m) TRUE

Adenine binds to thymine through how many hydrogen bonds? G to C?

2; 3

How is the bacterial chromosome organized?

- DNA forms loop domains (microdomains) 1) circular, unfolded chromosome 2) looped 3) supercoiled

List the characteristics of prokaryotic chromosomes

- Single circular chromosome - Condensed via super-coiling of various proteins - Transcription and translation occur simultaneously - HAPLOID (only one copy of each gene) - genomes organized into the operons - contain small amounts of repetitive DNA - nonessential prokaryotic genes commonly encoded on extrachromosomal plasmids

List the characteristics of Eukaryotic chromosomes

- multiple linear chromosomes - condensed in nucleus via histones - transcription in nucleus and translation in cytoplasm - DIPLOID ( two copies of each gene) - Some genomes are organized into operons but most are not - contain large amounts of noncoding and repetitive DNA - extrachromosomal plasmids are not common in euks

What chemical bonds are present in the double helix?

1) Covalent; in the bases, the sugars, and in the phosphodiester linkages 2) H-bonds; holds the base pairs together 3) Hydrophobic bonds; stacked base pairs produce a hydrophobic core which provides stability in the aqueous cytplasms

What are the functions of non-histone proteins?

1) Structural role: chromosome scaffold 2) Chromosome replication (ex: DNA Polymerases) 3) Chromosome segregation (ex: Kinetochore protein) 4) Largest group active in transcription

What is the function of telomeres?

1) protect the ends of DNA molecules from being degraded in euk. chromosomes 2) prevents the fusion of different chromosomes 3) facilitate replication of the ends of the linear DNA molecules without the loss of material - If exposed to high-energy radiation, the telomeres have been taken off and the DNA molecules have the chance of fusing together.

In B-form DNA, how many base pairs are present in one helical turn?

10 Z=12 A=11

List the histones that complete the octamer

2 molecules each of: H2a, H2b, H3, H4

How is chromatin packaged in eukaryotic chromosomes?

3 LEVELS 1) Package DNA as a (-) supercoil into NUCLEOSOMES (involves the octamer of histone proteins) 2) Additional folding/supercoiling of the nucleosome fiber (H1 is involved) 3) Non-histone chromosomal proteins form a scaffold that is involved in condensing the 30nm chromatin fiber(shortens the length of the DNA 7fold) into the tightly packed metaphase chromosomes

What is the complementary strand? 5'-GTCATGAC-3'

3'-CAGTACTG-5'

If it is known that a double stranded DNA sequence is 20% adenine, what percentage of the sequence is guanine?

30%

Which of the following is true about double stranded DNA? 50% of bases are purines 50% of DNA is C 25% of each (ATGC) [A+T]=[G+C] It will always be 25% T

50% of the bases are purines

A nucleosome is composed of how many total histone molecules?

8

By labeling T2 phage with radioactive isotopes, Hershey and Chase were able to tell that DNA was the genetic material when what was found in the cells of test organisms?

A) Labeled PHOSPHORUS Sulfur is found in proteins

How is it demonstrated that DNA is the transforming principle?

C) Treat extracts of type IIIS with different enzymes to look for loss of transforming factor

What is the function of centromeres?

Centromeres function as spindle-fiber attachment sites on chromosomes; (they are required for the separation of homologous chromosomes to opposite poles of the spindle during Anaphase 1 of meiosis, and for the separation of sister chromatids during anaphase of mitosis and anaphase 2 of meiosis)

The property of ____ of the DNA double helix makes DNA uniquely suited to store and transmit genetic information from one generation to the next

Complementarity

An experiment was performed by Frankel-conrat and workers to demonstrate that TMV uses RNA rather than DNA for its genetic material. What did they do?

D) Reconstituted TMV particles by mixing coat proteins of on strain of TMV with RNA from another strain and determining which strain led to a subsequent phenotype

What are the differences between DNA and RNA?

DNA: double stranded, has deoxyribose sugar, bases: A, T, G, C RNA: single stranded, has ribose sugar, bases: A, U, G, C HAS A 2'-OH

In terms of MNase digestion, a nucleosome protects more DNA than a chromatosome?

False

How did the experiments of Griffith differ from those of Avery, MacLeod, and McCarty? What did each contribute?

Griffith: Used IN VIVO experiments that showed there was a TRANSFORMING PRINCIPLE in the transformation of the mice. Avery & Friends: Used IN VITRO experiments to prove that DNA was the transforming principle. They isolated the transformation, inserted different enzymes. Only DNase disrupted the transformation.

Compare and contrast the 3 types of DNA

Helix direction ; bp/turn ; helix diameter A - right ; 11 ; 2.3 nm - found in high salt [ ] and when dehydrated B - right ; 10 ; 1.9 nm ; the most common in our cells Z - left ; 12 ; 1.8 nm; rich in GC bonds and contain alternate purine/pyrimidine residues

What is the molecular composition of the bacteriophage? Who discovered it?

Hershey and Chase discovered that the genetic makeup for the Phage 2 is DNA NOT PROTEINS!

The Z DNA form is:

LEFT HANDED, 12 base pairs/ turn

Nucleosome VS Chromatosome

NUCLEOSOME: DNA wrapped around an octamer of histone proteins (protects 146 base pairs- 1.65/1.75 turns) CHROMATOSOME: Nucleosome plus the H1 (thought to stabilize the complete nucleosome) - protects 166 base pairs

Which can distinguish between RNA and DNA?

Presence of 2'-OH

Purines have _____ rings and pyrimidines have ____ rings

Purines - double ring bases Pyrimidines (CUT) - single ring bases

The special sequence of centromeres provides what function?

Site for spindle fiber attachment

What allows DNA to be collapsed into a tight structure?

Supercoils

What is the genetic material of TMV (Tobacco Mosaic Virus) ? Who discovered it and how?

TMV's genetic material is RNA not proteins! Fraenkel-Conrat through a reconstitution experiment. Tobacco leaves were infected with reconstituted virus particles containing RNA (from type A viruses) & proteins (Type B). The progeny viruses were Type A, revealing RNA as the genetic makeup of TMV.

What is the function of negative supercoiling bacteria?

To condense the bacterial genome so it will fit into the cell

What are the unique structural features of telomeres?

They contain DNA sequence repeat units, (e.g. TTAGGG in humans)

What did Hershey and Chase do/discover?

They discovered that bacteriophages are composed of DNA and not proteins. They labeled the Phosphorus (component of DNA) and the Sulfur (component of Proteins). Only the Phosphorus was introduced during the viral replication, proving that it was composed of DNA and not proteins.

The difference between RNA viruses and viroids is:

Viroids do not have a protein coat

Who deduced that the structure of DNA is a double helix?

Watson and Crick

Why is the melting temperature of DNA directly dependent on the GC content?

Where AT has 2 hydrogen bonds, GC have 3. The 3 bonds take longer to break than the 2.

What did Watson and Crick do?

discovered the structure of DNA using the X-Ray diffraction's from Franklin and Wilkins, and the base comparison studies from Chargaff

Each nucleosome:

has 146 nucleotide pairs of DNA wrapped around the octamer of histones