CELL STRUCTURE

Common Features of Cells

All have plasma membrane (cell membrane)

All have nuclear region

All have cytoplasm

cytoplasm

cell membrane

nuclear region

STRUCTURE OF 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

Lipid bilayer

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PHOSPHOLIPIDS

STRUCTURE OF CELL MEMBRANE

CARBOHYDRATES

PROTEINS

Fluid – Mosaic Model of Cell Membrane: (by Singer and Nicholson)

• Proteins in the cell membrane do several different functions.

PROTEINS OF CELL MEMBRANE

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

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

• Small molecules such as– Water– Oxygen– Carbon dioxide– Glucose– Amino acids– Urea

• Molecules that can dissolve lipids such as – Alcohol – Ether

• Polymers

The molecules that CANNOT pass through the membrane

• Lipid molecules (fatty acids, glycerol) pass through cell membranes easily.

• Electrically neutral molecules enter and leave cells more easily than electrically charged ions.

• Fat soluable vitamins (A, D, E,K) can pass easier than water soluable vitamins.

• In animal cells (+) ions can pass easier than (-) ions.

Prevents the cell contents from interacting with the surrounding medium

Gives shape and mechanical strength to the cell

Controls the material transport

CYTOPLASM AND ORGANELLES

• Cytoplasm: – 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

CYTOPLASM AND ORGANELLES

• 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.

CYTOPLASM AND ORGANELLES

• 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

CYTOPLASM AND ORGANELLES

CYTOPLASM AND ORGANELLES

Cytoskeleton: • Microtubules are linked in parallel rows.

• In animal cells microfilaments are found. They play role in muscle contraction.

CYTOPLASM AND ORGANELLES

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

Function: Proteins synthesis Ribosomes are made of two subunits Bacterial cells have smaller ribosomes.

RIBOSOME

When there is no protein synthesis in the cell these subunits are separate from each other. They come together in order to be functional.

ENDOPLASMIC RETICULUM

ENDOPLASMIC RETICULUM

• 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)

ENDOPLASMIC RETICULUM

Functions:carries proteins to Golgi bodyprovides a pathway for the transport of

molecules throughout the cellsmooth ER synthesizes lipidsprovides support to the celldivides the cytoplasm into compartments

(different type of chemical reactions can take place at the same time)

plays role in the contraction of skeletal muscles

ENDOPLASMIC RETICULUM

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

MITOCHONDRIA

Golgi Body (Golgi apparatus)

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.

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.

Golgi Body

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.

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.

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.

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.

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.

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.

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.

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.

Vacuoles

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3. Storage vacuole:

In plants, toxic waste materials are stored in storage vacuoles.

They also store some pigments that give color to plant parts.

Vacuoles

They are found only in plant cells!!!

They are surrounded by double membrane.

There are three types of plastids:

Chloroplasts

Chromoplasts

Leucoplasts

PLASTIDS

Chloroplast

Grana Stroma

Outer membrane

Inner membrane

They contain the green pigment chlorophyll.

Chlorophyll converts the light energy into chemical energy (photosynthesis).

Chloroplast

Chloroplast

Grana: Stroma:

Outer membrane

Inner membrane

Formed with the foldings of thylakoid membranes

Include the chlorophyll pigment

Fluid-filling part

Include enzymes, DNA, RNA, ribosomes and other organic molecules

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.

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)

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

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

Cell Wall plants, fungi, algae and bacteria have cell wall

is not alive

main function: protects the cell, gives its shape, gives mechanical support

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 - -

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

Experiments on nucleus

I

Ameba (lives)

II

The cell is divided into

two as shown

I dies II lives

I

II

The cell is divided into

two as shown

Both cells die because nucleus is destroyed

The nucleus of the cell is removed

The cell dies

An ameba cell

A B C D

The Structure of a Nucleus

The Structure of a Nucleus

The nucleus has three main parts: Nuclear membrane Nucleoplasm (contains chromatin)Nucleolus

- 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

1. The nuclear membrane:

1. The nuclear membrane:

- fluid – filling part of the nucleus- includes water, protein, DNA, RNA,

minerals and nucleotides

2. Nucleoplasm:

- 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

3. Nucleolus (pl.Nucleoli):

nucleolus

Coiling starts

It is visible under light microscope

only during cell division

Histones

It is not visible under light microscope

(cannot be seen before and after

cell division)

Chromatin

strands

Chromatin

Chromosome

Relationship between mitochondria and chloroplast

CO2 + H2O

Glucose + O2

light energy

ATP (for cellular work)

Chloroplast

Mitochondria

Comparison of Mitochondria and Chloroplast

Mitochondria Chloroplast

DNA,RNA, Ribosome

Double membrane

Chlorophyll X ATP for cellular activities

X