Viral Replication Cycles Quiz

Viral Replication Cycles

• Viruses are acellular, parasitic particles, considered non-living until they invade a host for growth and reproduction.
• Bacteriophages (phages) infect bacteria only. Their structure includes a capsid head containing the nucleic acid genome, a tail sheath, and tail fibers.
• Phages can undergo lytic or lysogenic cycles, classified as temperate (non-virulent) or virulent phages respectively.

Lytic Cycle

• Temperate phages follow this cycle.
• Host bacterium is killed by cell lysis.
• No prophage stage.
• Phage genome replicates independently of host DNA.
• Phage genome completely controls host mechanisms.
• High phage genome productivity.
• Quick cycle with progeny virus production.
• Does not involve a lysogenic cycle.
• Five steps: adsorption (attachment), penetration (entry), phage replication/biosynthesis, maturation (assembly), and lysis (release).

Lysogenic Cycle

• Virulent phages follow this cycle.
• Host cell is not harmed initially.
• Phage genome integrates into host genome as a prophage. Bacteria with a prophage are called lysogens.
• Phage genome replicates along with host DNA.
• Phage genome does not fully take over host mechanisms.
• Low phage genome productivity.
• Time-consuming process; no immediate progeny production.
• Can transition to lytic cycle with induction (e.g., UV light, chemical treatment).

Phenotypes and Ghosts

• Prophage presence can cause changes to host phenotype, called lysogenic conversion.
• The empty phage particle outside the host bacterium is called a ghost.

Prokaryotic and Eukaryotic Cells

• All living things are composed of cells classified as prokaryotic or eukaryotic.
• Prokaryotic cells lack membrane-bound organelles, including a nucleus.
• Eukaryotic cells possess membrane-bound organelles, including a nucleus.
• Prokaryotic cells have DNA located in the nucleoid region.
• The nucleoid is a region within the cytoplasm, lacking a membrane and containing DNA, proteins (including enzymes), and RNA.
• DNA in the nucleoid is organized by associating with proteins called histones.
• Supercoiling compacts DNA for fitting within the nucleoid.
• Topoisomerases nick DNA to relax supercoiling (for processes like transcription).

Rhizoids

• Rhizoids are filamentous structures on non-vascular plants (mosses, liverworts, hornworts) and some fungi and algae.
• Their primary function is anchoring to a substrate, and in some species, also absorbing water and nutrients through capillary action (osmosis and diffusion).
• Rhizoids grow from epidermal cells of the gametophyte.
• Rhizoids are ancient structures likely preserved from when plants transitioned to terrestrial life from aquatic life.

Mitochondria

• Mitochondria are double-membrane organelles found in eukaryotic cells (like human cells) in the cytoplasm.
• Mitochondria are thought to have originated from bacteria, evidenced by their double membrane and binary fission reproduction.
• Outer mitochondrial membrane has porins for mineral and protein passage.
• Inner mitochondrial membrane has enzymes for ATP production and is highly folded (cristae).
• The mitochondrial matrix contains mitochondrial DNA and enzymes involved in energy production, as well as calcium storage.
• Intermembrane space is the space between the membranes.
• Mitochondria produce ATP (energy currency) including processes like the citric acid cycle (Krebs cycle).
• Mitochondria also regulate apoptosis by releasing cytochrome C.
• Mitochondria store calcium; they regulate calcium levels in cells.

Enzymes

• Enzymes are specialized proteins that catalyze reactions by lowering activation energy.
• Activation energy is the minimum energy needed for a reaction to occur.
• Enzymes bind to substrates at the active site, forming an enzyme-substrate complex. The lock-and-key or induced fit model describes how this occurs.
• Products are formed and released, leaving the enzyme unchanged to repeat the process.

Sexual and Asexual Reproduction

• Reproduction can be sexual (two parents) or asexual (one parent).
• Offspring result from reproduction.
• Mitosis creates identical daughter cells (asexual).
• Meiosis produces gametes (sex cells) for sexual reproduction.
• Gametes are oocytes (female) and spermatocytes (male).
• Meiosis halves the genetic information during gamete formation.
• Zygote formation (fertilization of gametes) yields a cell with all parental DNA.
• A zygote develops into an embryo via mitosis, creating genetically similar (but not identical) offspring.
• Sexual reproduction increases survival chances for a species.

Plant Reproductive Structures

• Antheridium is the male reproductive structure in many plants (flowering and non-flowering).
• Antheridium produces sperm cells in spermatogenesis.
• Archegonia are the female reproductive structures which produce egg cells.
• Gametophytes are the sexual phase of alternation of generations. They have a haploid number of chromosomes.
• Antheridia are found in Bryophytes and cryptogams (nonflowering plants).
• Plants have alternation of generations life cycles, alternating between sexual and asexual phases.
• Water is needed for sperm to reach eggs for fertilization in some plants.

Mitosis and Meiosis

• Mitosis is a single cell division process producing two identical daughter cells from one parent cell (somatic cells).
• Meiosis is a two-round cell division process that produces four different daughter cells (reproductive cells).
• Crossing over occurs during prophase I of meiosis, leading to genetic variation.
• Key stages in mitosis and meiosis include prophase, metaphase, anaphase, and telophase.

Cell Cycle

• The cell cycle is a process of cell division resulting in two genetically identical daughter cells.
• Interphase, mitosis, and cytokinesis are the three main stages of the cell cycle.

Interphase, Mitosis and Cytokinesis in Detail

• Interphase prepares the cell for mitosis, comprising G1, S, and G2 phases.
• G1: cell growth, basic metabolism, G1 checkpoint.
• S: DNA synthesis and duplication.
• G2: production of intracellular materials and organelles, G2 checkpoint (checks for DNA damage).
• M: Mitosis (prophase, prometaphase, metaphase, anaphase, telophase, and cytokinesis).
• Prophase: chromosome formation. Chromosomes appear as X shapes under microscope
• Prometaphase: nuclear envelope breakdown.
• Metaphase: chromosomes align at metaphase plate.
• Anaphase: sister chromatids separate.
• Telophase: nuclear membrane reassembles, cell splits.
• Errors in mitosis can result in aneuploidy, nondisjunction, and trisomy.
• Endoreplication is a form of mitosis used by some organisms in response to stress.

Protista

• Protista kingdom encompasses single-celled, eukaryotic organisms that aren't plants, animals, or fungi.
• Protists are polyphyletic (don't share a single ancestry).
• Protists share the characteristic of being eukaryotic cells, meaning they have membrane-bound organelles, including a nucleus.

Energy and Matter

• All living organisms need constant energy and matter input for survival and reproduction.
• The sun provides ultimate energy via photons.
• Plants (autotrophs) use photosynthesis to convert sunlight to usable energy.
• Photosynthesis uses carbon dioxide and water to produce sugar and oxygen.
• Consumers (heterotrophs) obtain energy from plants or other animals.
• Energy and matter are recycled in ecosystems when organisms die.

Homeostasis

• Homeostasis is maintaining a stable internal environment, crucial for biological function.
• Cell membranes help maintain homeostasis through molecular transport (passive and active transport).
• Passive transport (diffusion, facilitated diffusion): no energy required.
• Active transport: energy required.

Feedback Mechanisms

• Feedback mechanisms maintain homeostasis through responses to changes.
• Negative feedback maintains a target level (e.g., body temperature).
• Positive feedback amplifies changes away from a target level (e.g., fruit ripening).

Energy Transformation

• Organisms need energy for survival and reproduction.
• The sun provides energy for photosynthesis, an endergonic reaction.
• Cellular respiration, an exergonic reaction, breaks down sugar to make ATP. ATP is the usable energy for cells.
• Photosynthesis and cellular respiration are linked, creating a continuous energy cycle.

Cellular Respiration

• Cells, particularly eukaryotes, need oxygen to produce ATP (energy) from food molecules like glucose.
• Cellular respiration is the breakdown of organic molecules to produce ATP.
• Aerobic respiration, which requires oxygen, involves glycolysis, the transition reaction, Krebs cycle, and oxidative phosphorylation.
• Anaerobic respiration, which occurs without oxygen, uses a different electron acceptor instead of oxygen and may involve fermentation.

Photosynthesis

• Photosynthesis is the process where plants and some protists and bacteria use sunlight to convert energy into food (sugar).
• Chlorophyll absorbs light, especially blue and red wavelengths (reflects green). Chlorophyll is located in the thylakoid membrane of chloroplasts.
• Chlorophyll energizes electrons, which is critical to the steps of photosynthesis.
• In essence, photosynthesis is cellular respiration in reverse, transforming sunlight into energy storage.

Genetics

• Homozygous: an organism has two identical alleles for a particular gene. Example: BB, bb.
• Heterozygous: an organism has two different alleles for a particular gene. Example: Bb.
• Dominant trait: expressed in heterozygous genotypes.
• Recessive trait: not expressed in heterozygous genotypes.