The first two precepts of Cell Theory were enunciated near the middle of the 19th century, after many observations of plant and animal cells revealed common structural features (e.g., a nucleus, a wall or boundary, a common organization of cells into groups to form multicellular structures of plants and animals and even lower life forms). These precepts are
- Cells are the basic unit of living things;
- Cells can have an independent existence.
The 3rd statement of cell theory had to wait until late in the century, when Louis Pasteur disproved notions of spontaneous generation, and German histologists observed mitosis and meiosis, the underlying events of cell division in eukaryotes: Cells come from pre-existing cells (i.e., they reproduce).
- Cell and Molecular Biology – MCQ Questions with Answers
- Cell and Molecular Biology – Short Questions with Answers
This article provides a quick review of the important definitions and terms used in the study of Cell and Molecular Biology.
Gel like substance enclosed within the cell membrane excluding nucleus.
2. Plasma membrane
It is the biological membrane that separates the interior of the cell from the outside environment.
The cell that lacks a distinct nucleus and other specialized membrane bound organelles.
An organism whose cell contains a membrane bound distinct nucleus along with other specialized organelles enclosed in membranes.
The in-folding of plasma membrane in some bacterial cells that carry respiratory enzymes.
It is a group of ribosomes associated with a single messenger RNA during the translation process.
The process by which a cell engulfs a solid particle to form an internal vesicle known as phagosome is called phagocytosis, also called eating of cell.
The process of intake of liquid into a cell by the budding of small vesicles from the cell membrane is called pinocytosis, also called drinking of cell.
In the process of exocytosis materials are exported outside the cell by using energy from ATP molecules.
When the genetic material is transferred from one bacterial cell to other either by direct contact or by a bridge like connection between two cells is called conjugation.
11. Plasma membrane
A microscopic membrane made up of lipids and proteins which forms the external boundary of the cytoplasm of a cell or encloses a vacuole, and regulates the passage of molecules in and out of the cytoplasm.
The ability of a barrier to let any substance pass through it.
An atom or molecule with a net electric charge due to the loss or gain of one or more electrons.
14. Semi permeable
Allowing certain substances especially small molecules or ions to pass through it but not others, especially allowing the passage of a solvent but not of certain solutes.
A receptor is a protein molecule in a cell or on the surface of a cell to which a substance such as a hormone, a drug, or an antigen can bind, causing a change in the activity of the cell.
Having the property of transmitting electric force without conduction.
The substances that have an affinity for water due to the formation of hydrogen bonds.
Hydrophilic molecules typically have polar groups enabling them to readily absorb or dissolve in water as well as in other polar solvents.
It is an aggregate of molecules in a colloidal solution, such as those formed by detergents.
20. Peripheral proteins/extrinsic proteins
Peripheral membrane proteins are proteins that adhere only temporarily to the biological membrane with which they are associated. These molecules attach to integral membrane proteins, or penetrate the peripheral regions of the lipid bilayer.
21. Integral proteins/intrinsic proteins
An integral membrane protein (IMP) is a type of membrane protein that is permanently attached to the biological membrane. All trans membrane proteins are IMPs, but not all IMPs are trans membrane proteins.
It is the property of a molecule having both polar (water-soluble) and non polar (not water-soluble) affinities in its structure.
The proteins which acts as catalysts within living cells and increases the rate of biochemical reactions.
24. Plasma membrane
The membrane forming the surface of cytoplasm and consisting of a bimolecular phospholipids layer between an inner and outer layer of protein molecules.
The nerve cell with its outgrowths, structural unit of nervous system.
26. Adenosine Triphosphate (ATP)
A molecule containing high energy bonds that provides energy for many biochemical cellular processes by undergoing enzymatic hydrolysis.
A muscular or ligamentous partition that separates the thorax from the abdomen in mammals.
In a sarcomere, I-band is the zone of thin filaments that is not superimposed by thick filaments.
Myofibrils are the rod like units of muscle cells. They are composed of repeating sections of sarcomere, which appear under the as dark and light bands.
Oocyte is a female gametocyte or an immature ovum involved in reproduction. It is produced in the ovary during female gametogenesis and it undergoes meiotic division to form an ovum.
A vesicle is a small structure within a cell, consisting of fluid enclosed by a lipid bilayer membrane.
The beta barrel proteins that acts as transport protein which cross a cellular membrane and act as a pore through which molecules can diffuse. Porins are large enough to act as channels that are specific to different types of molecules.
The permease is membrane transport proteins that facilitate the diffusion of a specific molecule in or out of the cell by passive transport.
Cardiolipin is an important component of the inner mitochondrial membrane where it constitutes about 20% of the total lipid composition. It is essential for the optimal function of numerous enzymes that are involved in mitochondrial energy metabolism.
A cristae is a fold in the inner membrane of the mitochondrion. It provides a large amount of surface area for the chemical reactions to occur on.
It is a structural unit of cellular cristae.
37. De novo
De novo is a Latin expression meaning “from the beginning,” “afresh,” “anew,” “beginning again.”
A microbody is a type of organelle that is found in the cells of plants, protozoa and animals and microbody include peroxisome, glyoxysome and glycosome.
39. Endoplasmic reticulum
It is a network of membranous tubules within the cytoplasm of a eukaryotic cell, continuous with the nuclear membrane. It usually has ribosomes attached and is involved in protein and lipid synthesis.
A ribosome is a protein synthesizing machine found within all living cells that serves as the site of biological protein synthesis.
41. Golgi Bodies
The Golgi bodies also called Golgi complex or Golgi apparatus is a system of membranes like ER. It receives proteins and lipids from rough endoplasmic reticulum, modifies some of them and sorts, concentrates and packs them into vesicles.
It is an organelle bounded by double membrane in which the biochemical processes of respiration and energy production occur.
Plastids are double membrane organelle found in the cells of plants and algae. They are the site of manufacture and storage of important chemical compounds like pigments used in photosynthesis.
It is an organelle where cell microtubules get organized. It regulates the cell division cycle, the stage which lead up to cell division. They occur only in animal cells.
A lysosome is a membrane bound cell organelle found in most animal cells. They are spherical vesicles containing hydrolytic enzymes capable of breaking down all kinds of bimolecular, including proteins, nucleic acids, carbohydrates, lipids and cellular debris.
In invertebrates and plant cells, Golgi complex usually consists of many isolated units called dictyosome. They are scattered throughout the cytoplasm.
Cisternae refer to a flattened membrane discs lying stacked upon each other like pancakes.
These are the short structures arising from the periphery of the cisternae. Some of these enlarge at their ends to form vesicles.
The vesicles are the spherical structures that lie near the ends and concave surface of the Golgi complex. They are pinched off from the tubules of the cisternae.
50. Interstitial cells
Any cells that lie between other cells are called interstitial cells. For e.g. Leydig cells that produce testosterone are found adjacent to the somniferous tubules of testicle.
An electrolyte is a substance that produces an electrically conducting solution when dissolved in a polar solvent, such as water. The dissolved electrolyte separate into cations and anions and are dispersed uniformly through the solute.
52. Goblet cells
A goblet cell is a glandular, columnar epithelial cell whose function is to secrete gel-forming mucins, the major components of mucus.
It is the process by which body converts the food into energy. During this complex biochemical process, calories in food are combined with oxygen to release the energy for the body to function.
Oxidation is the loss of electrons by a molecule, atom, or ion.
Exocytosis is a process by which a cell directs the contents of secretary vesicles out of the cell membrane and into the extracellular space.
The desmotubule is a tube of appressed endoplasmic reticulum that runs between two adjacent cells. Some molecules are known to be transported through this channel, but it is not thought to be the main route for plasmodesmatal transport.
Dalton is the standard unit that is used for indicating mass on an atomic or molecular scale (atomic mass). One unified atomic mass unit is approximately the mass of one nucleon (either a single proton or neutron) and is equivalent to 1 g/mol.
58. Sedimentation Coefficient
The sedimentation coefficient of a particle is used to characterize its behavior in sedimentation processes, notably centrifugation. It is defined as the ratio of a particle’s sedimentation velocity to the acceleration that is applied to it.
Ribonuclease is a type of nuclease that catalyzes the degradation of RNA into smaller components.
An organelle in the cytoplasm of eukaryotic cells containing degrading or hydrolyzing enzymes enclosed in a membrane.
Matrix is the material in animal or plant cells, in which more specialized structures are embedded. A specific part of the mitochondrion that is the site of oxidation of organic molecules is also called matrix.
Plasmalemma is the cell membrane that surrounds the cytoplasm of living cells, physically separating the intracellular components from the extracellular environment.
It is a cylindrical cell structure composed mainly of a protein called tubulin.
Phagocytosis is the process by which a cell engulfs a solid particle to form an internal vesicle known as a phagosome.
The ingestion of liquid into a cell by the budding of small vesicles from the cell membrane.
Autophagy allows the orderly degradation and recycling of cellular components. During this process, targeted cytoplasmic constituents are isolated from the rest of the cell within a double-membrane vesicle known as an autophagosome.
White blood cells are also called leucocytes. These are the cells of the immune system that are involved in protecting the body against both infectious diseases and foreign invaders.
Macrophages are the type of white blood cells that engulf and digest cellular debris, foreign substances, microbes, cancer cells, and anything else that does not have the types of proteins specific of healthy body cells on its surface.
Metamorphosis is a biological process by which an animal physically develops after birth or hatching, involving a conspicuous and relatively abrupt change in the animal’s body structure through cell growth and differentiation.
Kinetosome forms the base of the flagellum, consisting of a circulararrangement of microtubules.
A dimer is a chemical structure formed from two similar subunits.
72. Metabolic pathway
A sequence of chemical reactions undergone by a compound or class of compounds in a living organism.
73. Electron microscope
A microscope that uses a beam of accelerated electrons as a source of illumination is known as electron microscope. As the wavelength of an electron can be up to 100,000 times shorter than that of visible light photons, the electron microscope has a higher resolving power than a light microscope and can reveal the structure of smaller objects.
74. Pericentriolar satellite
Pericentriolar satellites are electron-dense granules that are concentrated around the centrosome. They are involved in the recruitment of centrosomal proteins and microtubule organization the interphase stage of the cells.
Neutrophil are the most abundant type of granulocyte and the most abundant type of white blood cell in most mammals. They form an essential part of the innate immune system.
A double membrane at the boundary of the nucleoplasm is called karyolymph. It has regularly spaced pores covered by a disc-like nuclear pore complex and a space between the two membranes; the outer membrane is continuous at intervals with the rough endoplasmic reticulum.
It is the fluid or gel-like substance of the nucleus in which the chromatin material, nucleolus, and other particulate elements of the nucleus are suspended.
It is a ring-shaped object, structure, or region. Heterochromatin: Heterochromatin represents relatively inactive parts of the chromosomes. They stain darker than others and remain coiled and compacted in the interphase.
The uncoiled chromatin fibers, extended and scattered in the nucleoplasm represent the euchromatin (true chromatin) of the interphase nucleus. They are stained lightly.
80. Constitutive heterochromatin
The DNA of constitutive heterochromatin is permanently inactivated and remains in the condensed state at all times. Facultative heterochromatin: Heterochromatin that is partly condensed and inactivated is called facultative heterochromatin.
81. DNA linker
Linker DNA is double-stranded DNA in between two nucleosome cores that, in association with histone H1, holds the cores together.
82. Histone proteins
Histones are highly alkaline proteins found in eukaryotic cell nuclei that package and order the DNA into structural units called nucleosomes.
83. Chromatin fiber
A complex of macromolecules found in cells consisting of DNA, RNA and proteins.
84. Nucleic acid
The biopolymers, which include DNA (deoxyribonucleic acid) and RNA (ribonucleic acid), made from nucleotides are known as nucleic acids.
Any of a group of viruses whose nucleic acid core is composed of RNA, including the retroviruses and picornaviruses is known as ribovirus.
The nucleoid is an irregularly shaped region within the cell of a prokaryote that contains all or most of the genetic material and it is not surrounded by a nuclear membrane.
87. Extra nuclear Chromosomes
Extra chromosomal DNA is any DNA that is found outside of the nucleus of a cell like in mitochondria and plastids.
The centrosome is an organelle that is the main place where cell microtubules get organized.
A kinetochore is a protein structure that forms on a chromatid during cell division and allows it to attach to a spindle fiber on a chromosome.
A satellite chromosome or SAT chromosome has a chromosome segment that is separated from the main body of the chromosome by a secondary constriction.
91. Nuclear organizer
A nucleolar organizer is a chromosomal region around which the nucleolus forms.
At each end of a chromosome there is a region of repetitive nucleotide sequences which protects the end of the chromosome from deterioration or from fusion with neighboring chromosomes. This region is known as telomere.
93. Malpighian tubule
The Malpighian tubule system is a type of excretory and osmoregulatory system found in some insects, myriapods, arachnids, and tardigrades. It consists of branching tubules extending from the alimentary canal that absorbs solutes, water, and wastes from the surrounding haemolymph.
A chromomere is one of the serially aligned beads or granules of a eukaryotic chromosome, resulting from local coiling of a continuous DNA thread.
It is the division of nucleus during cell cycle.
Division of cytoplasm that separates the daughter cells following division of parent cells. Genome: Genome is defined as complete set of gene or genetic material present in a cell.
A protein structure that divides the genetic material in a cell. The spindle is necessary to equally divide the chromosomes in a parental cell into two daughter cells during both types of nuclear division: mitosis and meiosis.
Asters are star like cellular structures, formed around each centrosome during mitosis in an animal cell. Astral rays, composed of microtubules, radiate from the centrospheres.
99. Meristematic tissues
A meristematic tissue in most plants contains undifferentiated cells and is found in zones of the plant where growth can take place.
The organs that produces gametes (sperms and ovum); i.e. testis or ovary. Nucleosomes: In eukaryotic cells the chromosomes consisting of a length of DNA are coiled around a core of histones. This structural unit is called nucleosome.
It is a microscopic network of protein filaments and tubules in the cytoplasm of many living cells.
102. Somatic cell
The cells of a living organism other than the reproductive cells are known as somatic cells.
103. Germ cell
These are haploid cells that have the capacity to unite with the germ cell of the opposite sex and reproduce new individual. These are also called gametes.
It is a protein structure present on chromosomes and is a by which they are attached to spindle fibers.
It is a minute, one-celled, reproductive unit that is capable of giving rise to a new individual without sexual fusion and is the characteristic of protozoans, fungi and lower plants.
A pair of homologous chromosomes.
During the first metaphase of meiosis, chromosomes remain in contact at certain points at which crossing over and exchange of genetic material occur between the strands. These points are called chiasmata.
Deoxyribonucleic acid, the information carrying genetic material that comprises the genes Genetics- the science of heredity and variation
A hereditary determinant of a specific biological function, a unit of inheritance located in a fixed place on the chromosome.
110. Nucleic acid
A macromolecule composed of phosphoric acid, pentose sugar, and organic bases, DNA and RNA.
A unit of DNA and RNA molecules containing a phosphate, a sugar, and an organic base
A duplication process that is accomplished by copying from a template
(Ribonucleic acid) the genetic information carrying material in some viruses, non genetic RNA is generally derived from DNA by transcription that may carry information (mRNA),
114. Provide sub
Cellular structure (rRNA), transport amino acids (tRNA), or facilitate the biochemical modification of itself or other RNA molecules (enzymes).
Cytoplasmic organelle on which proteins are synthesized
Non translatable part of mRNA in eukaryotic cells
117. Exons- translatable part of mRNA in eukaryotic cell
Formation of RNA from one strand of DNA
Splicing removal of introns to join together all exons to form functional mRNA in eukaryotes
SNRPs are small nuclear ribonucleo proteins that combine with unmodified PmRNA and other proteins to form spliceosomes
Spliceosome is a complex of snRNAs and proteins, found in eukaryotic cells. It helps in removing introns from PmRNA
A substance of low molecular weight that inactivates a repressor by combining with it, thereby stimulating gene expression
123. Inducible enzyme
An enzyme that is synthesized only in the presence of the substrate that acts as an inducer.
Any substance or product that retards a chemical reaction or modifier gene that interferes with a reaction
A nucleotide sequence to which RNA polymerase binds and initiates transcription, Also, a chemical substance that enhances the transformation of benign cells into cancerous cells
A part of an operon that controls the activity of one or more structural genes by binding a regulatory protein
A group of genes making up a regulatory or control unit, includes an operator, a promoter, and structural genes.
128. Repressible enzyme
An enzyme whose synthesis is diminished by a regulatory molecule
129. Regulator gene
A gene that controls the rate of expression of another gene or genes, Example- the lac I gene produces a protein that controls the expression of the structural genes of the lac operon in Escherichia coli.
130. Anti codons
Three bases in a transfer RNA molecule that are complementary to the three bases of a specific codon in messenger RNA.
Codons are set of three adjacent nucleotides in an mRNA molecule that specifies the incorporation of an amino acid in to a polypeptide chain or that signals the end of polypeptide synthesis. Codons with the latter function are called termination codons.
Mutation is a change in the DNA at a particular locus in an organism. The term is used loosely to include point mutations in a population.
133. Wobble hypothesis
Hypothesis to explain how one tRNA may recognize two codons. The first two bases of the mRNA codon and anti-codon pair properly, but the third base in the anticodon has some play (or wobble) that permits it to pair with more than one base.