Exam 2 Review Questions

11/04/2025

Proceeding from the chromosome theory of inheritance, which were the two main candidate molecules for the genetic material? Explain briefly. 

Proteins - diverse, better studied, though to be genetic material in1940s

Nucleic Acids (DNA) - discovered earlier but thought too simple at first

In the process of bacterial transformation, what is the transforming agent and why is it so?

DNA, transformation is a genetic event, broad range of variation (changes are transferred into next generations) 

What is the essence of Griffith’s in vivo transformation experiments?

Griffith (1927): live non-virulent bacteria became virulent when mixed with heat-killed virulent cells → transformation in vivo

What is the essence of Avery-McLeod-McCarty in vitro transformation experiments?

Avery, MacLeod, McCarty (1944): proved DNA caused transformation in vitro

Explain the Hershey-Chase bacteriophage experiments

Used T2 phages (50% DNA, 50% protein).

Labeled DNA with ³²P and protein with ³⁵S.

Only DNA entered bacteria, not protein.

Proved DNA, not protein, is the genetic material in prokaryotes.

Hershey-Chase bacteriophage experiments importance for the discovery that DNA carries the genetic information in prokaryotes.

DNA is the universal genetic material in prokaryotes and eukaryotes.

Name the 3 main points of the Transforming Principle

Transformation is a genetic event

It can transfer changes to the next generations

Transformation occurs in many bacteria and traits (antibiotic resistance, morphology, etc.)

What were the direct proofs that DNA is the genetic material in prokaryotes?

Bacterial transformation (Griffith, Avery)

Phage infection with labeled DNA/protein (Hershey-Chase) 

Transfection (infection of bacteria with purified phage DNA)

What are the three indirect proofs that DNA is the hereditary material in eukaryotes?

DNA is found in nucleus, mitochondria, chloroplasts (where genes are)

DNA amount correlates with ploidy (gametes vs somatic cells)

UV mutagenesis: DNA absorbs UV at 260nm (same as peak mutation rate)

What are the direct proofs that DNA is the genetic material in eukaryotes?

Recombinant DNA → bacteria make eukaryotic proteins

Transgenic/knockout animals show inheritance of modified DNA

Define C-value

total amount of DNA per haploid genome

Define C-value paradox

DNA amount does not always correlate with organism complexity

True or False: DNA is the universal genetic material. Explain.

False. Most organisms use DNA, but some viruses use RNA (HIV, COVID-19, Ebola)

The building units of all nucleic acids are ……………………………

Nucleotides

Name the 3 structural components of a NUCLEOTIDE.

Nitrogenous base

Pentose sugar 

Phosphate group

Know the three types of nucleoside phosphates

NMP, NDP, NTP

what is the importance of triphosphates in biological systems.

(ATP, GTP) = precursors for nucleic acids and main energy carriers in cells 

What is the structural basis for the ability of DNA to store an enormous amount of genetic information?

Sequence arrangement of 4 nucleotides in long chains = enormous combinations 

Give a formula for all possible nucleotide arrangements in a polynucleotide with 1523 nucleotides

4¹⁵²³

Give a formula for all possible nucleotide arrangements in a polynucleotide with human haploid genome

4³,⁰⁰⁰,⁰⁰⁰,⁰⁰⁰

Which molecule is in the 5’ end and which one in the 3’ end of the DNA polynucleotide chain?

5’ end → phosphate group

3’ end → hydroxyl group (-OH)

Base composition studies of DNA revealed 3 important properties. Name those.

The amount of Adenine is proportional to Thymine and the amount of Guanine is proportional to the amount of Cytosine (A = T and G = C) 

The sum of purines equals the sum of pyrimidines ((A+G) = (C+T))

The sum of (G+C) does not necessarily equal the sum of (A+T) ((G+C)  does not equal (A+T))

Know the main components and features of DNA double helix based on Watson-Crick model.

right-handed helix, two antiparallel strands 

bases stacked 3.4 Å apart

One full turn = 34 Å (10.4 bases/turn)

Diameter = 20 Å

Complementary base pairing: A–T, G–C

Major and minor grooves alternate

True or False: The diameter of the double helix is 34Å.

False. (20 Å)

True or False: There are two hydrogen bonds between each pair of nitrogenous bases

False. (A-T has 2, G-C has 3)

True or False: DNA is a right-handed double helix and each complete turn of the helix is 34Å

True

True or False: The percentage of G+C equals the percentage of A+T in the DNA molecule

False. (They do not have to be equal due to the variability of base pair composition.)

True or False: It is formed by two parallel strands, each starting with 5’ phosphate group (PO4) and ending with 3’ hydroxyl (OH) group.

False. (antiparallel)

True or False: The sum of purines equals to the sum of pyrimidines.

True

True or False: DNA strands are complementary due to specific pairing of A with G, and T with C.

False (A-T, G-C)

True or False: The amount of adenine (A) is proportional to the amount of Thymine (T) and the amount of Guanine (G) is proportional to the amount of Cytosine (C).

True

What is ‘complementarity’ and how important it is for the DNA molecule?

specific base pairing (A-T, G-C) due to specific chemical affinity between nitrogenous bases

important for replication, gene expression, meiotic pairing, molecular hybridization, and more 

DNA strands are antiparallel. Explain this.

one chain runs 5’ → 3’, the other runs 3’ → 5’ in the opposite direction. Important in DNA replication, transcription, and repair 

A double-stranded DNA has a base composition of 20% Guanine (G). What is the percentage of Adenine (A) in this sample?

if G = 20%, then C = 20% 

G + C = 40 % 

(A +T) = 100% - 40% = 60% 

A = 30%, T = 30%

What are the main structural differences between the DNA and RNA molecules?

DNA → deoxyribose sugar, bases: A T G C, double-stranded

RNA → ribose sugar, bases: A U G C, single-stranded

Which property of DNA structure allows DNA denaturation?

hydrogen bonds between base pairs can be broken by heat/ chemicals

Which property of DNA structure allows DNA renaturation?

complementary single strands will reassociate again into double helix

depends on genome size, depends whether DNA is repetitive or unique

Name one environmental condition that causes DNA to denature.

heat

Denaturing GC-rich DNA requires higher temperature than denaturing AT-rich DNA. Why?

G-C has 3 hydrogen bonds, stronger than A-T (2 bonds)

What is re-association kinetics and which two genome characteristics influence it the most?

speed at which single-stranded DNA re-anneals

influenced by genome size and repetitiveness of sequences 

Name the two properties of the DNA molecule that underlie molecular hybridization

Watson-Crick DNA base pairing complementarity principle (A-T and G-C) 

Denaturation / Renaturation 

True or False: 97% of the mammalian genome is composed of non-protein-coding sequences.

True

Which property of DNA allows its movement in the electric field? Towards which electric pole will DNA fragments migrate when electricity is applied to the sample?

DNA is negatively charged (phosphate groups) 

moves toward the positive electrode

If different size DNA fragments are loaded into agarose gel and placed in the electric field, which of the fragments – the smallest or the largest – will move the fastest?

smallest DNA fragments 

If data (e.g., textbook) are converted into DNA sequence for storage, what method is used to retrieve the data and convert it back into text?

The process is called DNA data storage or retrieval, which involves sequencing the DNA and decoding it back into a readable format. \

high price, DNA instability

How much E. coli DNA can theoretically store all World’s data?

one kilogram (1kg) of DNA