Microbiology Exam 2 Study Guide – Step-by-Step Guidance

Q1. Describe the structure of DNA.

Background

Topic: DNA Structure

This question tests your understanding of the molecular structure of DNA, including its components and how they are arranged.

Key Terms and Concepts:

• DNA (Deoxyribonucleic Acid)

• Nucleotide: composed of a phosphate group, deoxyribose sugar, and a nitrogenous base

• Double helix structure

• Base pairing

Step-by-Step Guidance

1. Start by identifying the three main components of a DNA nucleotide: phosphate group, deoxyribose sugar, and a nitrogenous base.

2. Recall that DNA is made up of two strands forming a double helix, with the strands running in opposite directions (antiparallel).

3. Consider how the nitrogenous bases pair with each other via hydrogen bonds (A with T, G with C).

4. Think about how the sugar-phosphate backbone forms the sides of the helix, while the bases form the rungs.

Try solving on your own before revealing the answer!

Final Answer:

DNA is a double-stranded molecule composed of nucleotides, each containing a phosphate group, a deoxyribose sugar, and a nitrogenous base. The two strands are antiparallel and form a double helix. The nitrogenous bases pair specifically (adenine with thymine, guanine with cytosine) via hydrogen bonds, while the sugar and phosphate groups form the backbone of each strand.

Q2. What are the five nitrogenous bases, and what are they attached to?

Background

Topic: Nitrogenous Bases in Nucleic Acids

This question focuses on identifying the five nitrogenous bases found in nucleic acids and understanding their attachment within the nucleotide structure.

Key Terms:

• Nitrogenous bases: Adenine (A), Thymine (T), Guanine (G), Cytosine (C), Uracil (U)

• Deoxyribose (in DNA) or ribose (in RNA)

• Nucleotide structure

Step-by-Step Guidance

1. List the five nitrogenous bases: four found in DNA and RNA, and one unique to RNA.

2. Recall that each base is attached to a sugar molecule (deoxyribose in DNA, ribose in RNA).

3. Consider how the base and sugar together form a nucleoside, and when a phosphate group is added, it becomes a nucleotide.

Try solving on your own before revealing the answer!

Final Answer:

The five nitrogenous bases are adenine, guanine, cytosine, thymine, and uracil. In DNA, adenine, guanine, cytosine, and thymine are present, while uracil replaces thymine in RNA. Each base is attached to a five-carbon sugar (deoxyribose in DNA, ribose in RNA) at the 1' carbon position.

Q3. How do nitrogenous bases bond to one another, and to whom do they bond? What is this called?

Background

Topic: Base Pairing in DNA

This question tests your knowledge of complementary base pairing and the type of bonds involved in holding the DNA strands together.

Key Terms and Concepts:

• Hydrogen bonds

• Complementary base pairing

• Purines and pyrimidines

Step-by-Step Guidance

1. Recall which bases pair together in DNA (A with T, G with C) and in RNA (A with U).

2. Identify the type of bond (hydrogen bond) that holds the base pairs together.

3. Think about the term used to describe this specific pairing (complementary base pairing).

Try solving on your own before revealing the answer!

Final Answer:

Nitrogenous bases bond to each other via hydrogen bonds: adenine pairs with thymine (or uracil in RNA) and guanine pairs with cytosine. This is called complementary base pairing.

Q4. What is the structure and function of plasmids?

Background

Topic: Plasmids in Prokaryotes

This question examines your understanding of plasmids, their structure, and their role in microbial genetics.

Key Terms:

• Plasmid: small, circular, double-stranded DNA molecule

• Extrachromosomal

• Gene transfer

Step-by-Step Guidance

1. Describe the physical structure of plasmids (shape, size, and DNA type).

2. Explain where plasmids are found (mainly in prokaryotes, sometimes in eukaryotes).

3. Discuss the function of plasmids, including their role in gene transfer and antibiotic resistance.

Try solving on your own before revealing the answer!

Final Answer:

Plasmids are small, circular, double-stranded DNA molecules found in prokaryotes (and some eukaryotes). They exist independently of the chromosomal DNA and often carry genes that confer advantages, such as antibiotic resistance or the ability to metabolize unusual substances.

Q5. Compare and contrast eukaryotic and prokaryotic chromosomes.

Background

Topic: Chromosome Structure in Different Cell Types

This question tests your ability to distinguish between the organization and features of chromosomes in eukaryotes and prokaryotes.

Key Terms:

• Chromosome: DNA molecule containing genetic information

• Linear vs. circular DNA

• Nucleoid, nucleus

Step-by-Step Guidance

1. Identify the number and shape of chromosomes in prokaryotes (usually one, circular) and eukaryotes (multiple, linear).

2. Describe where chromosomes are located in each cell type (nucleoid vs. nucleus).

3. Consider the presence of histone proteins and other packaging differences.

Try solving on your own before revealing the answer!

Final Answer:

Prokaryotic chromosomes are typically single, circular DNA molecules found in the nucleoid region, lacking histones. Eukaryotic chromosomes are multiple, linear DNA molecules located in the nucleus and are associated with histone proteins for packaging.