🦠 Fundamental Cytology: Prokaryotes, Eukaryotes, and Viruses

What is the biological discipline that studies cells, their organelles, and their vital processes?

Cytology, also known as cell biology.

In 1665, who first discovered dead cells in cork and introduced the term 'cell'?

Robert Hooke.

Who, in 1677, was the first to observe unicellular organisms, which he termed 'animalcules'?

Antoni van Leeuwenhoek.

Which two scientists are credited with the initial formulation of cell theory in 1838-1839, stating that plants and animals are made of cells?

M.J. Schleiden and Theodor Schwann.

What fundamental principle of cell theory did Rudolf Virchow state in 1855 with the phrase 'omnis cellula e cellula'?

That every cell arises from a pre-existing cell.

What are the three generally accepted tenets of modern Cell Theory?

1. The cell is the fundamental unit of life; 2. All organisms are made of one or more cells; 3. Cells arise from other cells through division.

What are the three main additions in the expanded version of the modern cell theory?

1. Genetic material is passed to daughter cells; 2. All cells have the same basic chemical composition; 3. Energy flow occurs within cells.

What constant component of plant cells was observed by Robert Brown in 1833, a critical discovery for cell theory?

The nucleus.

Prokaryotic cells are characterised by their genetic material being suspended in the cytoplasm in a region called the _.

nucleoid

What are the three basic bacterial shapes?

Spheres (cocci), rods (bacilli), and spirals (spirochetes).

How are bacteria classified based on their need for oxygen?

Aerobes (need oxygen), anaerobes (cannot survive in oxygen), and facultative bacteria (can live with or without oxygen).

What is the primary method of reproduction for most bacteria?

Binary fission, where a cell duplicates its DNA and divides into two.

What is the function of flagella in bacteria?

They are used for locomotion.

What is the function of pili (or fimbriae) on the surface of bacteria?

They are important for adhesion to host surfaces.

What protective advantage does an outer capsule confer to some bacteria?

It confers resistance to phagocytosis.

The bacterial cell wall is a protective layer composed of _ that prevents osmotic lysis.

peptidoglycan

What is the name for the small, circular, extrachromosomal DNA molecules found in bacteria?

Plasmids.

What type of ribosomes are found in the cytoplasm of bacterial cells?

70S ribosomes.

What are endospores, produced by Bacillus and Clostridium species?

They are heat-resistant, dehydrated resting cells containing a genome and essential metabolic machinery.

The process by which a vegetative bacterial cell converts into a spore during unfavourable conditions is called _.

sporulation

The core of an endospore contains high amounts of calcium and dipicolinic acid, which form what protective compound?

Calcium dipicolinate.

What is the role of Small Acid-Soluble Proteins (SASPs) in the core of an endospore?

They bind to and condense DNA, protecting it from damage and providing nutrition for germination.

What is the main structural difference in the cell wall between Gram-positive and Gram-negative bacteria?

Gram-positive bacteria have a thick peptidoglycan layer, whereas Gram-negative bacteria have a thin layer and an outer membrane.

In Gram-positive bacteria, what acidic polymers are linked to the peptidoglycan and cell membrane?

Teichoic acids and lipoteichoic acids.

The outer membrane of Gram-negative bacteria contains a complex macromolecule called _, which is also an endotoxin.

lipopolysaccharide (LPS)

What is the principal reason Gram-positive bacteria retain the crystal violet-iodine complex during Gram staining?

The thick, highly cross-linked peptidoglycan layer becomes dehydrated by alcohol, trapping the large dye complex inside.

What is the role of safranin in the Gram staining procedure?

It acts as a counterstain, colouring the decolorised Gram-negative bacteria pink or red.

Bacterial peptidoglycan consists of a glycan backbone of repeating disaccharides of N-acetylmuramic acid (NAM) and _.

N-acetylglucosamine (NAG)

The lipid A component of LPS is responsible for what activity in Gram-negative infections?

Endotoxic activity, which can cause endotoxic shock.

What is the periplasmic space in Gram-negative bacteria?

It is the space located between the peptidoglycan layer and the outer membrane, containing various proteins.

A bacterium with a single flagellum at one pole is described as having a _ arrangement.

monotrichous

A bacterium with many flagella distributed over its entire surface is described as having a _ arrangement.

peritrichous

The bacterial flagellum consists of what three main parts?

The filament, the hook, and the basal body.

In the basal body of a Gram-negative bacterium's flagellum, which ring is anchored in the lipopolysaccharide layer?

The L-ring.

What is the primary function of sex pili in bacteria?

They are responsible for bacterial conjugation, acting as a conduit for DNA transfer.

Organisms are divided into two main classes: , which lack a nuclear envelope, and , which have a nucleus.

prokaryotic cells; eukaryotic cells

What are the two major groups of prokaryotes?

Archaebacteria and Eubacteria.

According to the prevailing hypothesis, what molecule is believed to have been the initial genetic system for the first cell?

RNA.

Organisms that derive their energy from the oxidation of chemical fuels are known as _.

chemotrophs

Organisms that can obtain all their necessary carbon from $CO2$ are known as .

autotrophs

Chemotrophs that derive energy from oxidising inorganic compounds are classified as _.

lithotrophs

Humans and E. coli are classified as _ because they require organic compounds for both energy and carbon.

chemoorganoheterotrophs

What term describes viruses as acellular infectious agents that require a host cell to multiply?

Obligate intracellular parasites.

A viral genome is surrounded by a protein coat known as a _, which is composed of smaller units called capsomers.

capsid

What is a nucleocapsid?

The combination of a virus's capsid and its genome.

What is a complete virus particle, with all components needed for host cell infection, called?

A virion.

What are the two primary types of viral symmetry?

Helical symmetry and icosahedral symmetry.

What is the term for a viral genome that consists of several nucleic acid segments?

A multipartite genome.

A single-stranded RNA virus is described as _ if its genome can serve directly as mRNA.

sense (or positive sense)

What are the five general steps of the viral replication cycle?

Attachment, penetration, synthesis, assembly, and release.

What is a bacteriophage?

A virus that infects bacteria.

In the _ cycle, a bacteriophage always lyses the host cell at the end of replication.

lytic

In the lysogenic cycle, the integrated viral DNA within the host's chromosome is known as a _.

prophage

What is the process called when a prophage is triggered by stressful conditions to enter the lytic cycle?

Induction.

A _ infection in eukaryotes is when the virus co-exists peacefully with the host cell for a long period, similar to lysogeny.

latent

Some enveloped viruses are released one at a time from a host cell in a budding process, causing a _ infection where the virus is produced for a long time.

persistent

What is the term for a virus that can cause cancer?

An oncovirus.

Oncoviruses can cause cancer by producing proteins that inactivate host proteins known as _, which normally regulate cell growth.

tumour suppressor proteins

The distinguishing features of eukaryotic cells are the nucleus and a variety of _ organelles.

membrane-bounded

What theory explains the origin of mitochondria and chloroplasts in eukaryotic cells?

The theory of endosymbiosis.

According to endosymbiosis theory, mitochondria evolved from engulfed aerobic _.

bacteria

According to endosymbiosis theory, chloroplasts evolved from engulfed photosynthetic _.

cyanobacteria

Name three structures found in plant cells but not typically in animal cells.

Cell wall, central vacuole, and chloroplasts.

What is the term for a group of similar cells that work together to perform a specific function?

Tissue.

What is the term for a group of different tissues that work together to perform a specific physiological function?

Organ.

A _ consists of all the living things (biotic factors) in a given area, together with the nonliving environment (abiotic factors).

ecosystem

Biological membranes are described as _ permeable because they retain certain compounds while excluding others.

selectively

The characteristic trilaminar appearance of a cell membrane in an electron micrograph consists of two electron-dense layers separated by a _ central region.

clear (less dense)

All lipid molecules in cell membranes are _, meaning they have both a hydrophilic and a hydrophobic end.

amphipathic

When mixed with water, amphipathic lipids can spontaneously form spherical micelles, bimolecular sheets called bilayers, or hollow spheres called _.

vesicles or liposomes

In membrane glycerolipids, the third hydroxyl group of glycerol is esterified by phosphoric acid, to which a polar _ is attached.

head

What type of lipid, common in animal cell membranes, consists of a rigid polycyclic ring structure and a hydrocarbon tail?

Cholesterol.

How does cholesterol affect the permeability and deformability of the lipid bilayer?

It enhances the permeability barrier and makes the bilayer less deformable by restricting hydrocarbon chain mobility.

_ membrane proteins are embedded directly within the lipid bilayer, often spanning it completely.

Integral

_ membrane proteins are associated indirectly with the membrane through interactions with integral proteins or lipid head groups.

Peripheral

What is the name for the cell coat formed by glycoproteins and glycolipids on the extracellular side of the plasma membrane?

The glycocalyx.

Who proposed the fluid mosaic model of membrane structure in 1972?

Jonathan Singer and Garth Nicolson.

What does the 'fluid' aspect of the fluid mosaic model refer to?

It refers to the ability of both lipids and proteins to move laterally within the plane of the membrane.

What effect does increasing the number of unsaturated fatty acids have on membrane fluidity?

It increases membrane fluidity because the kinks in the chains prevent tight packing.

The rare migration of a phospholipid molecule from one monolayer of the membrane to the other is known as _.

flip-flop

The plasma membrane is described as _ because the lipid and protein composition differs between the inner and outer monolayers.

asymmetric

In the erythrocyte plasma membrane, which two choline-containing lipids are typically found in the outer leaflet?

Phosphatidylcholine and sphingomyelin.

Empty red blood cell membranes, used for studying plasma membranes, are referred to as _.

ghosts

The movement of lipids where they exchange places with their neighbours within a single monolayer is called _.

lateral diffusion

In the basal body of a flagellum, which pair of proteins acts as the motor and which acts as the motor switch?

The 'Mot' protein causes motor rotation, and the 'Fli' protein acts as a motor switch.

What is the key difference in function between fimbriae and pili?

Fimbriae are primarily for attachment and adherence, while sex pili are specifically for bacterial conjugation.

Eukaryotic viruses like HIV use the enzyme _ to convert their RNA genome into DNA, which is then integrated into the host genome.

reverse transcriptase

The integrated viral DNA from a retrovirus within a host cell's genome is called a _.

provirus

What is an episome, as seen in latent infections by Herpesviruses?

An unintegrated, circular piece of viral DNA that remains in the host cell nucleus.

What is the term for inward folds of the bacterial plasma membrane, now largely considered to be artefacts of chemical fixation?

Mesosomes.

Unlike eukaryotic cell membranes, most bacterial membranes lack sterols and instead contain sterol-like molecules called _.

hapanoides

In the Gram staining procedure, what chemical is used as the primary stain?

Crystal violet.

In the Gram staining procedure, what chemical is used as the mordant to form a complex with the primary stain?

Iodine.

What substance is typically used as the decoloriser in the Gram staining procedure?

95% ethyl alcohol or an alcohol-acetone mixture.

What is the process of programmed cell death, essential for tissue remodelling and regeneration, called?

Apoptosis.

Organisms that trap and use sunlight for energy are known as _.

phototrophs

Cyanobacteria are classified as because they use sunlight for energy and $CO2$ for carbon.

photolithoautotrophs