Ch:14 DNA and RNA

Question 1

Chromosomes contain large numbers of genes which represent the ___(3 words)___

Answer 1

Fundamental heredity unit

Question 2

__(2 words)__ is a polymer made from monomeric units called nucleotides.

Answer 2

Nucleic acids

Question 3

Which of the following has 3 hydrogen bonds?

A. G-C
B. A-T

Answer 3

A. G-C

Question 4

The ____ bonds and ____ interactions between the stacked bases inside the helix stabilizes the helical structure.

Answer 4

H-bonds and hydrophobic interactions

Question 5

As we __increase/decrease__ the percent of GC we increase stability and melting point, since more hydrogen bonds are in GC than AT!!

Answer 5

Increase

A = T regions will be the first to melt and break!!

Question 6

Is DNA found in bacteria or viruses?

Answer 6

YES both

Question 7

If a DNA sample has 20% cytosine, what is the % of adenine?

Answer 7

30%

Question 8

Discuss the water solubility of:

• the phosphate group
• the ribosyl group
• the nitrogen base

Answer 8

The ribosyl group and phosphate group are polar and will be hydrophilic… they are located on the outside of our helix and are water soluble

Purines and pyrimidines are relatively insoluble in water (hydrophobic); located in the helix interior

Question 9

What biology or histology technique is used to identify chromosomal material or DNA?

Answer 9

We use the Feulgen stain. DNA stains reddish in color. Mild acid hydrolysis cleaves the molecule and a reaction reveals this red color.

Question 10

Write the complementary sequence for:

5’ GATCAA 3’

Answer 10

3’ CTAGTT 5’

***strands are anti-parallel

Question 11

DNA is wrapped around proteins called _____ which look like a bead with a string wrapped with it. This entire complex, DNA and histone = _________.

Answer 11

histones; nucleosome

Question 12

Explain the differences between heterochromatin and euchromatin:

Answer 12

Heterochromatin:

• Dark stained
• DNA is NOT actively transcribed
• located mainly near the nuclear envelope

Euchromatin:

• Eukaryotic, DNA is available for transcription
• “true chromatin”
• more dispersed and less compacted

Question 13

The famous ____________ experiment concluded that DNA and NOT protein is the actual genetic info!

Answer 13

Hershey-Chase experiment

Question 14

Discuss the Fred-Griffith Transformation Experiment:

Answer 14

When he killed a pathogenic bacteria with heat and mixed the cell remains with living non-pathogenic bacteria, some of these harmless bacteria became pathogenic!

He found out that the DNA of bacteria is what caused this transformation

Question 15

The _______ experiment in 1944 confirmed the work done by Fred Griffith to establish that DNA is indeed the genetic material.

Answer 15

Avery-McCarty experiment

Question 16

Discuss the differences between:

• rRNA
• tRNA
• mRNA

Answer 16

rRNA: provides physical makeup of the ribosome
- Most abundant

tRNA: transports amino acids to ribosomes
- smallest

mRNA: carries DNA info to ribosomes
- shortest lived

Question 17

Match rRNA, tRNA and mRNA to the following:

• Most abundant
• smallest
• shortest lived

Answer 17

rRNA = most abundant

tRNA = smallest

mRNA = shortest lived

Question 18

Why does alkaline conditions partially denature (i.e. unwinds DNA in certain areas) the helix?

Would the regions that unwind be richer in A-T or G-C?

Answer 18

By increasing the pH, we ionize some of the nucleic acid bases, and all of the phosphate groups, thus increasing the # of negatively charged groups, which promote unwinding of the helix to reduce charge repulsion!!!

• Richer in A-T bc it only has 2 H-bonds as opposed to G-C which has 3

Question 19

Which is more sensitive to base… DNA of RNA? Why?

Answer 19

RNA has a 2’ OH group that DNA lacks. This 2’ OH can launch an intramolecular attack

Question 20

DNA —> RNA in a process called _______ and occurs in the _______.

Answer 20

Transcription; nucleus

Question 21

How do histones bind so tightly to DNA?

Answer 21

Histones have positively charged amino acids and DNA is negatively charged which allows for tight binding