Cell Structure and its function Dr Kalpana B

Cell Structure and its function Dr. Kalpana. B Assistant professor Physiology

At the end of this class students should: • Draw labelled structure of a cell • Draw the structure of cell membrane and list its functions • List the functions of various cell organelles

LEVELS OF ORGANIZATION Living Levels: 1. CELL (makes up ALL organisms) 2. TISSUE (cells working together 3. ORGAN (heart, brain, stomach …) 4. ORGAN SYSTEMS (respiratory, circulatory …) 5. ORGANISM copyright cmassengale 3

Cell Structure • Cell Membrane • Cytoplasm • Nucleus

Cell or Plasma Membrane • Composed of double layer of phospholipids and proteins-(fluid mosaic model) • Controls what enters or leaves the cell Outside of cell Proteins Carbohydrate chains Cell membrane Inside of cell (cytoplasm) Protein channel copyright cmassengale Lipid bilayer 5

• Diameter 7. 5 nm • Made up of lipids and proteins • Lipids- 20 -40% phospholipids and cholesterol • Proteins-60 -70% • Lipoproteins • Glycoproteins • carbohydrates

Phospholipids • Heads contain glycerol & phosphate and are hydrophilic (attract water) • Tails are made of fatty acids and are hydrophobic (repel water) • Make up a bilayer where tails point inward toward each other copyright cmassengale 7

Functions • Contributes to semi-permeability nature of cell membrane. • Cholesterol-contributes to fluidity of membraneflexible.

Cell Membrane Proteins • Aid in cell recognition • Peripheral proteins • Integral proteins copyright cmassengale 9

ü INTRINSIC PROTEINS – ENZYMES ü PERIPHERAL PROTEINS- CYTOSKELETON ü TRANSMEMBRANE PROTEINS CHANNELS CARRIERS PUMPS RECEPTORS

Functions of proteins • • • Structural support As channels and pores. Carrier proteins Act as enzymes Receptors Helps in transmission of impulses.

Carbohydrate layer Found in combination with lipids and proteins Functions • Forms connection for adjacent cells-membrane junctions. • Form antigens • Receptors for binding hormones

Functions of the cell membrane • • PROTECTIVE FUNCTION AS A SEMI PERMEABLE MEMBRANE ABSORPTIVE FUNCTION-ABSORBS NUTRIENTS EXCRETORY FUNCTION-EXCRETES WASTES PRODUCT. • EXCHANGE OF GASES • MAINTENANCE OF SIZE AND SHAPE OF THE CELL • Links adjacent cells together by junctional complexes –tissues.

ORGANELLS IN CYTOPLASM • Membrane-bound intracellular compartments. • Contain specific chemicals to perform specific cellular function.

ENDOPLASMIC RETICULUM • Interconnected network of tubular and vesicular structure • Forms the link between nucleus and cell membrane Two types • Rough endoplasmic reticulum • Smooth endoplasmic reticulum

Functions of RER • Contains ribosomes • Anchorage of newly synthesize proteins. Functions of the SER • synthesis of lipids, processing of sugars, and detoxification of drugs and poisons • Site of steroid synthesis • sarcoplasmic reticulum

GOLGI APPARATUS • • • Cluster of flattened membranous sacs Stores, modifies and packages proteins Forms glycoprotein Acrosome in male germ cells Molecules transported to and from the Golgi by means of vesicles

LYSOSOMES • Digest foreign molecules & damaged organelles • Contain digestive enzymes-hydrolases • Digestion and removal of worn out and dead cells of tissue(auto digestion)

MITOCHONDRIA • Surrounded by a DOUBLE membrane • Folded inner membrane called CRISTAE –enhances enzymatic reaction. • Respiratory enzymes are present in cristae. • Cristae contains matrix • Matrix contains DNA and RNA • Power plant” of the cell

The Control Organelle Nucleus • Controls the normal activities of the cell • Contains the DNA Bounded by a nuclear envelope (membrane) with pores • Usually the largest organelle copyright cmassengale 21

Nuclear Envelope • Double membrane surrounding nucleus • Also called nuclear membrane • Contains nuclear pores for materials to enter & leave nucleus • Connected to the rough ER copyright cmassengale 22

• Each cell has fixed number of chromosomes that carry genes • Genes control cell characteristics copyright cmassengale 23

Inside the Nucleus The genetic material (DNA) is found copyright cmassengale 24

PEROXISOMES Function to rid the cell of toxic substanceshydrogen peroxide

RIBOSOMES • Protein synthesis machinery. • Free floating in cytoplasm. • Bound to rough-Endoplasmic Reticulum (RER) in Eukaryotes. • Consists of multiple subunits composed of RNA-protein complexes.

CENTROSOMES • Centrosome is the cellular organelles situated near the center of the cell close to the cell • Movement of the chromosome during cell division

CYTOSKELETON • Provides shape and structure • Helps move organelles around the cell • Made of three types of filaments

• References • Text Book of medical physiology-AP Krishna • Physiology for B. Sc. Nursing –Dr A. K jain