Nucleic Acids

Question 1

Two Types of Nucleic Acid

Answer 1

Deoxyribonucleic acid (DNA)
Ribonucleic acid (RNA)

Question 2

Prokaryotic vs Eukaryotic DNA

Answer 2

Prokaryotic Cells:

• Contained in nucleoid
• Plasmids
• Smaller circular chromosomes
  * Supercoiled

Eukaryotic Cell:

• Contained in the nucelus
• Large linear chromosomes

Overall, basic units of prokaryotic and eukaryotic genomes are the same.

Question 3

Supercoiling of DNA

Answer 3

Occurs in circular chromosomes of prokaryotes.

• Coiling that occurs in addition to coil of helical DNA structure
• Compacts DNA into a small space

Question 4

Maps of Bacterial Chromosomes

Answer 4

• Over 2000 bacterial strains have been fully sequenced to create maps
• Illustrates positions of genes on chromosome (metabolism, synthesis, etc)
• Genes outside of chromosome may help cell survive in unique environments/conditions

Question 5

The Griffith’s Experiment

Answer 5

Two strains of Streptococcus Pneumoniae: Virulent (S Strain) & benign (R Strain)

• S strain: Kills
• R strain: No effect
• S strain that was heated to kill bacteria (all macromolecules still present): No effect
• Killed S strain and living R strain combined: Kills
  * R strain picked up information (DNA) from dead S strain and became virulent through transformation
  * They did not know DNA was the hereditary macromolecule yet…

Discovered transformation and the presence of a hereditary macromolecule

Question 6

Transformation

Answer 6

Change in cell behaviour resulting from incorporation of genetic material from outside of the cell.

Question 7

How did we find out that DNA carries hereditary information? (Avery et al.)

Answer 7

• 3 tested macromolecules: proteins, RNA, DNA
• Each macromolecule selectively eliminated from killed virulent, and added to nonvirulent to see if transformation occurs
• Enzymes used to degrade specific macromolecule (RNase, protease, DNase)

Findings: Presence of DNA allowed transformation, absence of DNA halted transformation. Therefore DNA is the hereditary molecule in the cell.

Question 8

X-Ray Diffraction Experiments (Rosalind Franklin)

Answer 8

Aims X-Rays at DNA to create images based on diffraction of X-Rays by atoms in DNA molecule
* DNA’s helix shape identified
* Calculations made to determine dimensions

Question 9

Nucleotides

Answer 9

Basic subunits of DNA.
* Phosphate group, 5 carbon deoxyribose sugar, nitrogenous base

Question 10

Nitrogenous Bases

Answer 10

Pyrimidines: Cytosine (C), Thymine (T)
* Heterocyclic molecules
* Single ring

Purines: Guanine (G), Adenine (A)
* Two rings: Pyrimidine + imidazole ring
* Larger than pyrimidines

Question 11

Phosphodiester Bonds/Linkage

Answer 11

• Result of condensation reaction between two nucleotides in their polymerization
• Phosphate group on 5’ C on deoxyribose bonds w/ hydroxyl group on 3’ C on next deoxyribose
• Nitrogenous bases extend out from backbone and interact with eachother in double helix

Backbone has 5’ to 3’ polarity.

Question 12

Chargaff’s/Base-Pair Rules

Answer 12

Base-Pair Rule
* DNA of any cell should have a 1:1 ratio of pyrimidine and purine bases (G = C, A = T)
* Molecular pairing between pyramidine and purines
* 2 Hydrogen bonds between Adenine and Thymine
* 3 H bonds between Guanine and Cytosine

Calls for consistent spacing between the two backbones.

Question 13

Watson and Crick’s Double Helix DNA Structure

Answer 13

• Double Helix
• Two strands run antiparallel
• Bases face inwards
• Major and minor grooves

Question 14

Synthesis of RNA

Answer 14

Enzyme called RNA Polymerase transcribes DNA into different RNA’s
* mRNA, rRNA, tRNA

Question 15

DNA vs RNA

Answer 15

RNA
* Ribose sugar: Hydroxyl on 2’C
* Nucleotides are ribonucleotides: C–G, U – A
* Uracil has a hydrogen
* Single stranded

DNA
* Deoxyribose sugar: Hydrogen on 2’C
* Nucleotides are deoxyribonucleotides: C – G, T–A
* Thymine has methyl group
* Double stranded

Question 16

Messenger RNA or mRNA

Answer 16

• Single stranded
• Copy of genes that codes for a protein

Question 17

Transfer RNA or tRNA

Answer 17

• Folds into 3D structure due to base pairing between ribonucleotides
• Carry amino acids into ribosome
• Match amino acid to appropriate mRNA sequence
• Builds the polypeptide chain!

Question 18

Ribosomal RNA or rRNA

Answer 18

• Multiple rRNA and proteins form functional ribosome complexes
• Performs translation of mRNA into proteins

Question 19

Where is DNA found in Eukaryotes?

Answer 19

• Nucleus: Contains chromosomes
• Mitchondria and Chloroplasts: Contains own genetic material

Question 20

Storage of Eukaryotic DNA in Nucleus

Answer 20

• DNA coiled around histone proteins (8 histone = nucleosome)
• Multiple nucleosomes coiled to create chromatin fibre
• Coiling of chromatin creates metaphase chromosome

Question 21

Plasmids

Answer 21

Circular DNA molecules
* Carries 1-2 genes
* Replicate independently
* Transferred from one cell to another – rapid spread of genes (allows for antibiotic resistance)