Cell - The Unit of Life

Endoplasmic reticulum transport proteins and enzymes to their destinations i.e. within the cell and outside the cell.

Chemiosmotic coupling hypothesis is the most widely accepted explanation for oxidative phosphorylation in mitochondria and photophosphorylation in thylakoid membranes. Mitchell proposed the idea of chemiosmotic coupling. He suggested that a concentration gradient of protons is established across the mitochondrial membrane because there is an accumulation of hydrogen ions on one side of the mitochondrial membrane. The proton accumulation is necessary for energy transfer to the endergonic ADP phosphorylation process.

Flip-Flop movement is due to migration of lipid molecules from one lipid monolayer to other monolayer of lipid bilayer.

Telomeres are non sticky terminal ends of the chromosomes. It has heterochromatin and repetitive DNA.

The thylakoid membranes possess the chlorophylls. The outer membrane is permeable to a number of solutes. Inner membrane has a number of carrier proteins. Stroma forms the matrix containing the enzyme for Calvin cycle.

Totipotency is the ability of a living somatic plant cell to develop into a complete plant. It was first demonstrated by Steward et. al. (1964) using phloem cells of carrot. This technique is now used for multiplying rare and endangered plants through micro-propagations. This technique is widely used for multiplying plants e.g., Chrysanthemum, Dioscorea floribunda, Coleus, Crotons, carnation plants etc.

Nucleolus synthesizes and stores RNA. The ribosomal proteins are synthesized in the cytoplasm and shift to the nucleolus for the formation of ribosomal subunits by complexing with rRNA.

Fluid mosaic model of plasma membrane proposes that plasma membrane comprises of a phospholipid bilayer wherein icebergs of proteins float in the sea of phospholipids.

Middle lamella is the first formed layer, present between the two adjacent cells. It is situated outside the primary cell wall. It is made up of calcium and magnesium pectate.

Phytochrome is a plant pigment that can detect the presence or absence of light and is involved in regulating many processes that are linked to day length (photoperiod), such as seed germination and initiation of flowering. It consists of a light-detecting portion, called a chromophore, linked to a small protein and exists in two interconvertible forms with different physical properties, particularly in the ability to bind to membranes.

Glycosylation of protein means linking of sugars to proteins which starts in rough endoplasmic reticulum and completed in golgi complex.

A lysosome is a tiny sac bounded by a single unit membrane of lipoprotein. It contains a dense, finely granular fluid. The latter consists of glycoprotein hydrolytic (digestive) enzymes called acid hydrolases. These include proteases, lipases, nucleases, glycosidases, sulphatases, acid phosphatases, etc.

Ribosomes present in nuclear membrane and endoplasmic reticulum take part in protein synthesis. Two or more ribosomes simultaneously engaged in protein synthesis on the same mRNA strand forming polyribosomes. The ribosome functions as a template, bringing together different components required for protein synthesis.