Cell Structure and Organelles Practice Flashcards

Vocabulary-style flashcards covering cell structure, organelle functions, and fundamental differences between eukaryotes, prokaryotes, and viruses based on the lecture notes.

General cell theory

The theory stating that the Cell is the basic and functional unit of all living organisms.

Virchow's theory

The theory that all cells arise or come from existing cells by cell division.

Compartmentalization

The concept where organelles act as compartments that allow different metabolic reactions and functions to occur at the same time.

Nucleus

A cell organelle approximately $10\,\mu m$ in size that contains genetic material, controls cell activities, and houses the nucleolus.

Nuclear envelope

A double membrane surrounding the nucleus; the outer membrane is continuous with the endoplasmic reticulum.

Nuclear pores

Openings in the nuclear envelope that allow and control the exchange of substances between the nucleoplasm and the cytoplasm.

Nucleoplasm

The fluid within the nucleus containing chromatin, ions, $mRNA$, the nucleolus, proteins, and nucleotides.

Nucleolus

A non-membrane bound dense area of chromatin in the nucleus responsible for the formation of ribosomes.

Chromatin

Structure composed of $DNA$ coiled around histone proteins.

Rough Endoplasmic Reticulum (RER)

A network of flattened fluid-filled sacs called cisternae covered by ribosomes; functions in protein synthesis and transport.

Smooth Endoplasmic Reticulum (SER)

A network of tubular cisternae lacking ribosomes; involved in the synthesis of lipids and steroids like cholesterol, oestrogen, and testosterone.

Cisternae

Fluid-filled compartments or sacs that form the membranes of the endoplasmic reticulum and Golgi body.

Ribosomes

Organelles $20\text{--}25\,nm$ in size made of ribosomal $RNA$ and protein; they serve as the site of translation and protein synthesis.

Svedberg unit ($S$)

A unit representing the sedimentation rate of particles in a high-speed centrifuge; the larger the number, the heavier and larger the particle.

80S Ribosomes

Larger ribosomes found in Eukaryotic cells, typically $25\,nm$ in size.

70S Ribosomes

Smaller ribosomes found in Prokaryotic cells, mitochondria, and chloroplasts, typically $20\,nm$ in size.

Golgi body

A stack of flattened sacs (cisternae) with swollen ends that collects, modifies, and processes molecules (especially proteins) incoming from the RER.

Glycosylation

A modification process in the Golgi body where carbohydrates are added to proteins to form glycoproteins.

Golgi vesicles

Sacs that bud off the Golgi body to transport processed proteins in and out of cells with the help of the cytoskeleton.

Lysosomes

Simple spherical sacs ($0.1\text{--}0.5\,\mu m$) surrounded by a single membrane containing over $60$ hydrolytic digestive enzymes.

Hydrolases

Hydrolytic digestive enzymes including proteases, lipases, and nucleases that work best in acidic conditions ($pH\,4\text{--}5$).

Autolysis

The self-destruction of a cell after death (programmed cell death) by releasing lysosomal contents into the cytoplasm.

Autophagy

The process by which lysosomes engulf and break down faulty organelles or unwanted structures.

Mitochondria

Sausage-shaped organelles surrounded by a double membrane; the site of aerobic respiration and $ATP$ synthesis.

Cristae

Finger-like projections formed by the folding of the inner mitochondrial membrane to increase surface area for respiration.

Matrix

The internal solution of the mitochondria containing circular $DNA$, $70S$ ribosomes, and essential respiration enzymes.

Porins

Transport proteins in the outer mitochondrial membrane that form wide aqueous channels for small water-soluble molecules.

ATP synthase

Stalked particles found on the mitochondrial cristae that are associated with the synthesis of $ATP$.

Microtubules

Small, hollow, rigid cylinders ($25\,nm$) made of tubulin dimers ($\alpha$ and $\beta$) organized into $13$ protofilaments.

Centrioles

Structures $0.5\,\mu m$ long made of nine triplets of microtubules joined by fibrils, found only in animal cells.

Centrosome

A region outside the nucleus containing two centrioles that acts as a microtubule organizing center ($MTOC$).

Cytoskeleton

An essential structural component made of microtubules, actin filaments, and intermediate filaments that maintains cell shape.

Axoneme

The whole cylindrical structure of cilia and flagella composed of over $600$ polypeptides and a specific microtubule arrangement.

Basal bodies

Structures at the base of every cilium and flagellum, identical to centrioles, from which they grow.

Chloroplast

Elongated organelles ($3\text{--}10\,\mu m$) with a double membrane where photosynthesis occurs.

Thylakoids

Fluid-filled sacs in chloroplasts containing photosynthetic pigments like chlorophyll; site of the light-dependent stage.

Granum

A stack of thylakoids within the chloroplast.

Stroma

The fluid within a chloroplast containing $70S$ ribosomes and circular $DNA$; site of the light-independent stage.

Cell wall

A rigid, inelastic structure ($0.5\text{--}1\,\mu m$) made of cellulose fibers that provides mechanical support and prevents cells from bursting.

Plasmodesmata

Cytoplasmic channels formed by small holes in the cell wall that link plant cells together in the symplast system.

Tonoplast

The single membrane that surrounds the large central vacuole in plant cells.

Endosymbiont theory

The theory that mitochondria and chloroplasts are ancient bacteria now living inside larger cells, supported by their circular $DNA$ and $70S$ ribosomes.

Murein

A peptidoglycan (polysaccharide + amino acids) used to build the cell walls of prokaryotes.

Mesosomes

Infoldings of the prokaryotic cell membrane that carry out photosynthesis and aerobic respiration.

Plasmids

Small circles of $DNA$ in prokaryotes that can replicate independently and carry genes for antibiotic resistance.

Viruses

Acellular particles ($20\text{--}300\,nm$) consisting of a nucleic acid core ($DNA$ or $RNA$) surrounded by a protein coat.

Capsid

The protective protein coat of a virus made up of subunits called capsomeres.