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CELL STRUCTURE Common Features of Cells

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1 CELL STRUCTURE Common Features of Cells
All have plasma membrane (cell membrane) All have nuclear region All have cytoplasm cytoplasm nuclear region cell membrane

The cell membrane has a two-layered structure mainly made of protein, lipid and carbohydrate molecules Protein molecules are embedded in the lipid bilayer Carbohydrate molecules may branch out from the external surface of the membrane Carbohydrate chains bonded to lipids form glycolipids Carbohydrate chains bonded to proteins form glycoproteins

3 Lipid bilayer

Fluid – Mosaic Model of Cell Membrane: (by Singer and Nicholson) CARBOHYDRATES PROTEINS G L Y C O I P D G L Y C O P R T E I N PHOSPHOLIPIDS

5 Proteins in the cell membrane do several different functions.

Transport Proteins: Control the movement of substances through the cell membrane Receptor proteins: They bind with messenger molecules to begin or stop metabolic activities Enzymes: Catalyze reactions Structural proteins: Help bind the membrane to neighboring cells or structural elements in the cytoplasm Identity proteins: Distinguish the cell from other cells

7 Proteins of Cell Membrane

Selective permeability enables the cell to protect the inner balance (homeostasis).

The molecules that can pass EASILY through the cell membrane The molecules that CANNOT pass through the membrane Small molecules such as Water Oxygen Carbon dioxide Glucose Amino acids Urea Molecules that can dissolve lipids such as Alcohol Ether Polymers

Electrically neutral molecules enter and leave cells more easily than electrically charged ions. In animal cells (+) ions can pass easier than (-) ions. Lipid molecules (fatty acids, glycerol) pass through cell membranes easily. Fat soluable vitamins (A, D, E,K) can pass easier than water soluable vitamins.

11 Prevents the cell contents from interacting with the surrounding medium
Gives shape and mechanical strength to the cell Controls the material transport

Fluid-filling part of the cell Occupies the space between the membrane and the nucleus Includes the cytoskeleton, organelles and cytosol. 65-95% water Contains many substances (granular proteins mostly) Also contains carbohydrates, lipids, enzymes, minerals, vitamins and pigments


Organelles: In eukaryotic cells there are secondary compartments covered with cell membrane. These are called organelles. An organelle is the part of the cell which is responsible for a specific function.

Cytoskeleton: is the skeleton of the cell an interconnected system of protein fibers and thin strands gives cells their shape and internal organization composed of microtubules and microfilaments

Cytoskeleton: Microtubules are linked in parallel rows. In animal cells microfilaments are found. They play role in muscle contraction.

The cytoplasm of a eukaryotic cell includes the following organelles: ribosome endoplasmic reticulum mitochondrion Golgi bodies lysosome peroxisome vacuole plastids centrosome

18 RIBOSOME Tiny, granular structures
Found in all cells without any exception Made of RNA and protein Some are found freely in cytoplasm and some are attached to the ER Ribosomes are produced in nucleolus

19 RIBOSOME Function: Proteins synthesis
Ribosomes are made of two subunits Bacterial cells have smaller ribosomes. When there is no protein synthesis in the cell these subunits are separate from each other. They come together in order to be functional.



Made of cell membrane Found in all cells except red blood cells and bacterial cells Two types: Smooth ER (no ribosomes on it) Rough ER (ribosomes on the outer surface)

Functions: carries proteins to Golgi body provides a pathway for the transport of molecules throughout the cell smooth ER synthesizes lipids provides support to the cell divides the cytoplasm into compartments (different type of chemical reactions can take place at the same time) plays role in the contraction of skeletal muscles


25 MITOCHONDRIA is the place where aerobic cellular respiration takes place in eukaryotic cells surrounded by double-layered membrane inner membrane has foldings called cristae, which provides a large surface area for the chemical reactions the fluid that fills the interior space is called matrix matrix includes ribosomes, DNA, RNA and proteins can duplicate itself

26 Golgi Body (Golgi apparatus)

27 Golgi Body Consist of a stack of flat, membrane –enclosed sacs and small vesicles Present in all cells except blood and sperm cells Plant cells have more golgi than animal cells They have connections with the membranes of E.R.

28 Golgi Body Functions of golgi: Secretion
Modifiying the molecules like glycoproteins and glycolipids coming from the E.R, and releasing them to cytoplasm. The vesicles originating from the golgi moves towards the cell membrane and the cell mebrane expands. It forms lysosomes. Some vacuoles are formed by golgi. Helps formation of cell wall in plants.

29 Golgi bodies are highly developed in gland cells.
For ex, their number is very high in salivary glands. Gastric glands and cells which produce nectar in plants.

30 Lysosome They are spherical structures surrounded by a single membrane. They are formed by golgi. They contain hydrolytic (digestive) enzymes. When lysosomes burst and release these enzymes, the cell starts to digest itself. It is called autolysis. Mostly found in animal cells that make phagocytosis. For ex; humans white blood cells.

31 Lysosome Functions: They digest intracellular and extracellular molecules. They digest worn –out cell organelles. They function in defence of the cell. They are found at the head part of the sperm cells and let sperms hydrolizye the outer wall of the egg.

32 Lysosome Functions: They function in defense of the cell. For ex; white blood cells contain high no. of lysosomes They are found at the head part of the sperm cells and let sperms hydrolyze the outer wall of the egg.

33 Peroxisome They bud from the membranes of E.R.
As a result of breaking down amino acids and fatty acids, a highly toxic molecule, H2O2 (hydrogen peroxide) is produced. Peroxisomes contain catalase enzyme that breaks down H2O2. They are especially found in liver, heart and muscle cells in humans.

34 Vacuoles They are fluid filled organelles surrounded with single membrane. Minerals, waste products, nutrients and some pigments are stored in vacuoles. They are found both in animal and plant cells, but animal cells have smaller vacuoles than plant cells. The immature plant cells have small vacuoles. As the plant cell matures merge to form one big vacuole.

35 Vacuoles There are three types of vacuoles: 1. Digestive vacuole:
Found in unicellular organisms and white blood cells. They are formed when a food molecule is taken into the cell and it’s surrounded by the cell membrane.

36 Vacuoles 2. Contractile vacuole:
Found in unicellular organisms that live in fresh water. For ex:Paramecium They pump out the excess water that goes inside the organism. @

37 Vacuoles 3. Storage vacuole:
In plants, toxic waste materials are stored in storage vacuoles. They also store some pigments that give color to plant parts.

38 PLASTIDS They are found only in plant cells!!!
They are surrounded by double membrane. There are three types of plastids: Chloroplasts Leucoplasts Chromoplasts

39 Chloroplast They contain the green pigment chlorophyll.
Outer membrane Inner membrane Grana Stroma They contain the green pigment chlorophyll. Chlorophyll converts the light energy into chemical energy (photosynthesis).

40 Chloroplast

41 Chloroplast Grana: Stroma:
Outer membrane Inner membrane Grana: Stroma: Formed with the foldings of thylakoid membranes Include the chlorophyll pigment Fluid-filling part Include enzymes, DNA, RNA, ribosomes and other organic molecules

42 Chloroplast The main function of chloroplasts is photosynthesis. They convert light energy into chemical energy and store it in ATP. But the ATP produced in the chloroplasts never get out of this organelle. They are used in photosynthesis only.

43 Chromoplast They contain different color pigments that give red, yellow, orange color to different parts of plants. These pigments do not play role in photosynthesis. They are sensitive to light. When chloroplasts are exposed to sunlight they can turn into chromoplasts. (Ex. Green tomato Red tomato)

44 Leukoplasts Leucoplasts:
They are usually located at tissues that are not exposed to sunlight (ex: roots) They store starch, oil and other plant products. Ex:Potato starch Corn lipid Bean protein They can turn into chloroplast when they are exposed to light. Potato

45 Centrosome made up of two perpendicular cylinders called centrioles
contains microtubules located near the nucleus function in cell division they produce spindle fibers which moves the chromosomes during cell division plant cells don’t have centrosomes

46 Cell Wall plants, fungi, algae and bacteria have cell wall
is not alive main function: protects the cell, gives its shape, gives mechanical support

47 Only contractile vacuole
Bacteria Protists Fungi Plants Animals Ribosome E.R. - Mitochondrion Golgi body Lysosome Peroxisome Central vacuole Only contractile vacuole Digestive vacuole Plastids Centrosome Cell mambrane Cell wall

48 Nucleus DNA is located in nucleus in a eukaryotic cell.
usually cells have one nucleus. Bacteria, and mature red blood cells do not have nucleus. control center for cell metabolism and reproduction if it is removed the cell dies

49 Experiments on nucleus
A B C D The cell is divided into two as shown The cell is divided into two as shown The nucleus of the cell is removed An ameba cell I I II II Ameba (lives) I dies II lives Both cells die because nucleus is destroyed The cell dies

50 The Structure of a Nucleus

51 The Structure of a Nucleus
The nucleus has three main parts: Nuclear membrane Nucleoplasm (contains chromatin) Nucleolus

52 1. The nuclear membrane: - it is a double membrane which isolates the nucleus it has connection with the membrane of ER it has pores that provide the passage of mRNA and some proteins

53 1. The nuclear membrane:

54 2. Nucleoplasm: fluid – filling part of the nucleus
includes water, protein, DNA, RNA, minerals and nucleotides

55 3. Nucleolus (pl.Nucleoli):
dense mass of irregular size and shape produces ribosomes and involved in protein synthesis the cells which have a high metabolic rate have more nucleoli than the others nucleolus

56 It is visible under light microscope only during cell division
Histones Coiling starts Chromatin Chromosome Chromatin strands It is visible under light microscope only during cell division It is not visible under light microscope (cannot be seen before and after cell division)


58 Relationship between mitochondria and chloroplast
light energy Chloroplast Glucose + O2 CO2 + H2O Mitochondria ATP (for cellular work)

59 Comparison of Mitochondria and Chloroplast
DNA,RNA, Ribosome Double membrane Chlorophyll X ATP for cellular activities



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