Biology: Cell Structure and Functions

A comprehensive set of vocabulary flashcards covering the structural and functional units of life, eukaryotic and prokaryotic cell components, and the contributions of key scientists in structural biology.

Reductionist Biology

The physico-chemical approach to study and understand living organisms, applying concepts and techniques of physics and chemistry to describe biological processes in molecular terms.

G.N. RAMACHANDRAN

An outstanding figure in the field of protein structure and the founder of the ‘Madras school’ of conformational analysis of biopolymers who discovered the triple helical structure of collagen in $1954$.

Ramachandran plot

An analysis tool used by G.N. Ramachandran to determine the allowed conformations of proteins.

Cell Theory

A fundamental biological theory formulated by Schleiden and Schwann, later final shaped by Rudolf Virchow, stating that all living organisms are composed of cells and products of cells, and all cells arise from pre-existing cells.

Antonie Von Leeuwenhoek

The first person to see and describe a live cell.

Robert Brown

The scientist who discovered the nucleus in $1831$.

Matthias Schleiden

A German botanist who in $1838$ observed that all plants are composed of different kinds of cells which form plant tissues.

Theodore Schwann

A German Zoologist who in $1839$ concluded that animal cells had a thin outer layer (plasma membrane) and that the presence of a cell wall is a unique character of plant cells.

Rudolf Virchow

The scientist who in $1855$ first explained that cells divided and new cells are formed from pre-existing cells (Omnis cellula-e cellula).

Unicellular organisms

Organisms composed of a single cell capable of independent existence and performing all essential functions of life.

Eukaryotic cells

Cells that possess membrane bound nuclei and other membrane bound organelles like endoplasmic reticulum, mitochondria, and Golgi complex.

Prokaryotic cells

Cells that lack a membrane bound nucleus and membrane bound organelles; they are represented by bacteria, blue-green algae, mycoplasma, and PPLO.

Mycoplasmas

The smallest known cells, measuring only $0.3\,\mu m$ in length.

Plasmids

Small circular DNA molecules found in many bacteria outside the genomic DNA that confer unique phenotypic characters such as resistance to antibiotics.

Mesosome

A specialised differentiated form of cell membrane in prokaryotes formed by extensions of the plasma membrane (vesicles, tubules, lamellae) that help in respiration and DNA replication.

Cell envelope

A chemically complex, three-layered structure in prokaryotes consisting of an outermost glycocalyx, followed by the cell wall and the plasma membrane.

Glycocalyx

The outermost layer of the cell envelope which can be a loose sheath called the slime layer or a thick and tough layer called the capsule.

Gram positive bacteria

Bacteria that take up the gram stain during the staining procedure developed by Gram.

Flagella

Thin filamentous extensions from the cell wall of motile bacteria, composed of three parts: filament, hook, and basal body.

Pili

Elongated tubular surface structures in bacteria made of a special protein, not involved in motility.

Fimbriae

Small bristle-like fibres sprouting out of the bacterial cell that help in attachment to rocks or host tissues.

Ribosomes

Non-membrane bound organelles which are the site of protein synthesis; they are $70S$ in prokaryotes and $80S$ in eukaryotic cytoplasm.

Polyribosomes (Polysome)

A chain formed when several ribosomes attach to a single mRNA to translate it into proteins.

Inclusion bodies

Reserve material in prokaryotic cells stored in the cytoplasm without a membrane, such as phosphate granules, cyanophycean granules, and glycogen granules.

Fluid mosaic model

An improved model of cell membrane structure proposed by Singer and Nicolson in $1972$, where proteins move laterally within a quasi-fluid lipid bilayer.

Passive transport

The movement of molecules across the cell membrane along a concentration gradient without the requirement of energy.

Osmosis

The movement of water across a selectively permeable membrane by diffusion from higher to lower concentration.

Active transport

An energy dependent process (utilizing ATP) that transports molecules across the membrane against their concentration gradient, such as the $Na^{+}/K^{+}$ Pump.

Middle lamella

A layer mainly of calcium pectate that holds or glues neighbouring plant cells together.

Plasmodesmata

Structures that traverse the cell wall and middle lamellae to connect the cytoplasm of neighbouring plant cells.

Endomembrane system

A group of organelles whose functions are coordinated, including the endoplasmic reticulum, Golgi complex, lysosomes, and vacuoles.

Rough endoplasmic reticulum (RER)

An endoplasmic reticulum bearing ribosomes on its surface, actively involved in protein synthesis and secretion.

Smooth endoplasmic reticulum (SER)

An endoplasmic reticulum lacking ribosomes, serving as the major site for the synthesis of lipids and steroidal hormones.

Golgi apparatus

A reticular structure near the nucleus composed of flat cisternae that packages materials into vesicles for secretion or delivery to intracellular targets.

Lysosomes

Membrane bound vesicular structures rich in hydrolytic enzymes (lipases, proteases, carbohydrases) active at acidic pH for digesting macromolecules.

Tonoplast

The single membrane that binds the vacuole in plant cells.

Mitochondria

Double membrane-bound 'power houses' of the cell where aerobic respiration occurs and ATP is produced.

Cristae

Infoldings of the inner mitochondrial membrane that increase the surface area for enzymatic activity.

Plastids

Pigment-containing organelles found in all plant cells and euglenoides, classified into chloroplasts, chromoplasts, and leucoplasts.

Chloroplasts

Double membrane-bound organelles containing chlorophyll and carotenoid pigments responsible for photosynthesis.

Chromoplasts

Plastids containing fat soluble carotenoid pigments like carotene and xanthophylls, giving plants yellow, orange, or red colours.

Leucoplasts

Colourless plastids that store nutrients, including amyloplasts (starch), elaioplasts (oils/fats), and aleuroplasts (proteins).

Thylakoids

Flattened membranous sacs present in the stroma of the chloroplast, arranged in stacks called grana.

Svedberg’s Unit (S)

The sedimentation coefficient used for ribosomes, which indirectly measures density and size.

Cytoskeleton

An elaborate network of filamentous proteinaceous structures (microtubules, microfilaments, intermediate filaments) providing mechanical support and motility.

Axoneme

The core of cilia or flagella, usually containing a $9+2$ array of microtubules.

Centrosome

An organelle containing two cylindrical centrioles surrounded by pericentriolar materials, involved in forming the spindle apparatus.

Nuclear envelope

A double membrane structure with a $10$ to $50\,nm$ perinuclear space that separates the nucleus from the cytoplasm.

Nucleolus

A non-membrane bound spherical structure in the nucleoplasm that is the site for active ribosomal RNA synthesis.

Chromatin

A network of nucleoprotein fibres in the interphase nucleus containing DNA, histones, non-histone proteins, and RNA.

Centromere

The primary constriction of a chromosome that holds two chromatids together and possesses disc-shaped kinetochores.

Metacentric chromosome

A chromosome with a middle centromere forming two equal arms.

Sub-metacentric chromosome

A chromosome with a centromere slightly away from the middle, resulting in one shorter and one longer arm.

Acrocentric chromosome

A chromosome where the centromere is situated close to its end, forming one extremely short and one very long arm.

Telocentric chromosome

A chromosome possessing a terminal centromere.

Satellite

A small fragment of a chromosome that appears due to a non-staining secondary constriction at a constant location.

Microbodies

Minute, membrane-bound vesicles containing various enzymes, present in both plant and animal cells.