MMBS111 Unit 2 Study Guide: Biochemistry, Genetics, and Viruses in Microbiology

Chapter 2: Biochemistry Basics

Major Groups of Biomolecules: Structure and Function

Biomolecules are essential for cellular structure and function. The four main groups are carbohydrates, lipids, nucleic acids, and proteins. Each group has unique building blocks, bonds, and biological roles.

Biomolecule	Building Blocks	Bond Type	Major Example	Function
Carbohydrates	Simple sugars (monosaccharides)	Glycosidic bonds	Starch, glycogen, cellulose	Energy storage, structural support
Lipids	Fatty acids, glycerol	Ester bonds	Triglycerides, phospholipids, steroids	Energy storage, membrane structure, signaling
Nucleic Acids	Nucleotides	Phosphodiester bonds	DNA, RNA	Genetic information storage and transfer
Proteins	Amino acids	Peptide bonds	Enzymes, antibodies, structural proteins	Catalysis, structure, transport, regulation

• Primary structure: Linear sequence of amino acids in a polypeptide chain.

• Secondary structure: Local folding into alpha-helices or beta-sheets via hydrogen bonding.

• Tertiary structure: Overall 3D folding of a single polypeptide chain.

• Quaternary structure: Association of multiple folded polypeptide chains.

Example: Hemoglobin is a protein with quaternary structure, composed of four polypeptide subunits.

Chapter 5: Genetics

Genotype and Phenotype

Genotype refers to the genetic makeup of an organism, while phenotype is the observable physical and functional traits resulting from gene expression.

• Genotype: DNA sequence of an organism.

• Phenotype: Observable characteristics, such as morphology or metabolism.

Example: The presence of a gene for antibiotic resistance (genotype) results in the ability to survive antibiotic treatment (phenotype).

Prokaryotic vs. Eukaryotic Genomes

Genomes differ between prokaryotes and eukaryotes in complexity, structure, and organization.

Feature	Prokaryotes	Eukaryotes
Complexity	Simpler	More complex
Genome location	Nucleoid region	Nucleus
Chromosome structure	Circular DNA, plasmids	Linear chromosomes
Histone proteins	Absent	Present

Chapter 5: Structure of DNA and RNA Nucleotides

Components of a Nucleotide

Nucleotides are the building blocks of nucleic acids, consisting of a phosphate group, a five-carbon sugar, and a nitrogenous base.

• DNA: Deoxyribose sugar, bases A, T, C, G

• RNA: Ribose sugar, bases A, U, C, G

Feature	DNA	RNA
Sugar	Deoxyribose	Ribose
Bases	Adenine, Thymine, Cytosine, Guanine	Adenine, Uracil, Cytosine, Guanine
Strands	Double-stranded	Single-stranded
Directionality	5' to 3'	5' to 3'

Complementary and Antiparallel Strands

DNA strands are complementary (A pairs with T, C pairs with G) and run antiparallel (one strand 5' to 3', the other 3' to 5').

Chapter 5: DNA Replication in Prokaryotes

Steps of DNA Replication

DNA replication is a semi-conservative process involving several enzymes:

1. Unwinding of the DNA double helix

2. Stabilization of single strands

3. Synthesis of RNA primers

4. Elongation by DNA polymerase

5. Replacement of RNA primers with DNA

6. Joining of Okazaki fragments

Enzyme	Function
Helicase	Unwinds DNA at the origin of replication
Primase	Synthesizes RNA primers
DNA polymerase	Adds nucleotides to the growing DNA strand
Ligase	Joins Okazaki fragments on the lagging strand

Chapter 5: RNA Types and Transcription

Types of RNA

Type	Function
mRNA (messenger RNA)	Carries genetic code from DNA to ribosome
tRNA (transfer RNA)	Brings correct amino acid to ribosome during translation
rRNA (ribosomal RNA)	Forms part of the ribosome structure and catalyzes peptide bond formation

Transcription and Translation

Transcription is the synthesis of RNA from a DNA template. Translation is the process by which ribosomes use mRNA to synthesize proteins.

1. Initiation: RNA polymerase binds to promoter region.

2. Elongation: RNA strand is synthesized.

3. Termination: RNA polymerase detaches at terminator sequence.

Chapter 5: Horizontal Gene Transfer in Prokaryotes

Mechanisms of Horizontal Gene Transfer

Process	Description
Conjugation	Transfer of DNA via direct cell-to-cell contact
Transformation	Uptake of free DNA from the environment
Transduction	Transfer of DNA by bacteriophages (viruses)
Transposons	Mobile genetic elements that can move within the genome

Chapter 6: Viruses and Prions

Viruses as Nonliving Microbes

Viruses lack cellular structure and metabolism, and cannot reproduce independently. They require a host cell for replication, so they are not considered alive.

Characteristic	Viruses	Prokaryotes	Eukaryotes
Cells	No	Yes	Yes
Genome	DNA or RNA	DNA	DNA
Reproduction	Requires host cell	Binary fission	Mitosis/meiosis
Metabolism	No	Yes	Yes

Structure of Viruses

Viruses consist of a nucleic acid genome (DNA or RNA), a protein capsid, and sometimes a lipid envelope derived from the host cell membrane.

Viral Genetic Material and Replication

Viruses can have DNA or RNA genomes, which may be single- or double-stranded. Replication involves attachment, penetration, biosynthesis, assembly, and release.

Genetic Reassortment and Recombination in Viruses

Genetic reassortment occurs when viruses with segmented genomes exchange segments during co-infection, leading to new viral strains. Recombination involves exchange of genetic material between different viral genomes.

Chapter 6: Host Range and Pathogenesis

Host Range

Host range refers to the spectrum of host species or cell types a virus or pathogen can infect. Determined by specific interactions between viral surface proteins and host cell receptors.

Transmission and Life Cycles

Viruses can be transmitted via direct contact, vectors, or environmental routes. Bacteriophages may undergo lytic or lysogenic cycles.

Generalized Replication in Animal Viruses

1. Attachment to host cell

2. Penetration and uncoating

3. Biosynthesis of viral components

4. Assembly of new virions

5. Release from host cell

Acute, Latent, and Chronic Infections

• Acute infection: Rapid onset, short duration (e.g., influenza)

• Latent infection: Virus remains dormant, can reactivate (e.g., herpesvirus)

• Chronic infection: Persistent infection with ongoing viral production (e.g., hepatitis B)

Additional info: These notes cover foundational concepts in biochemistry, genetics, and virology relevant to introductory microbiology courses, including molecular structure, gene expression, and viral replication.