The Cell

Cell Structure & Function

Dr. Sunita Bhagat JR 1st year

Cell Structure & Function

What is a cell? • Smallest unit of life that can carry out all the functions of a living thing. • Various sizes and shapes • Organism- living thing – Unicellular – multicellular

Microscope Development • 1665 – Robert Hooke named cell • 1674 – Anton von Leeuwenhoek - looked at cells in pond water and blood and published his observations

Cell Theory Developed • 1838 – Schleiden – all plants are made of cells • 1839 – Schwann – all animals are made of cells

• 1855 – Virchow – all cells come from pre-existing cells

Modern Cell Theory • Cells are the basic units of all life. • All organisms are made of one or more cells • All cells come from pre-existing cells

Microscopes • Hand lens • Compound light microscope

Examples of Cells Amoeba Proteus Plant Stem

Bacteria

Red Blood Cell

Nerve Cell

Two Types of Cells •Prokaryotic •Eukaryotic

Types of Cells • Prokaryotic – Simple cell – No membrane-bound organelles – Chromosome not contained in nucleus – Small cells – Ex - bacteria

• Eukaryotic – Complex cell – Membrane-bound organelles – Chromosomes contained in nucleus – Larger cells – Ex – all other organisms

Prokaryotic • Do not have structures surrounded by membranes • Few internal structures • One-celled organisms, Bacteria

Eukaryotic • Contain organelles surrounded by membranes • Most living organisms Plant

Animal

Animal Cell

Eukaryotic Cell

Eukaryotic Cell Plant Cell

“Typical” Animal Cell

A animal cell ENDOPLASMIC RETICULUM (ER)

Rough ER Flageliu m

Smooth ER

Nuclear envelope Nucleolu s Chromati n

NUCLEU S

Plasma membrane

Centrosom e CYTOSKELETO N Microfilament s Intermediate filaments Microtubules

Ribosome s

Microvill i Golgi apparatus

Peroxisom e Mitochondrio n

Lysosome

In animal cells but not plant cells: Lysosomes Centrioles Flagella (in some plant sperm)

“Typical” Plant Cell

• A plant cell NUCLEUS

Nuclear envelope Nucleolu s Chromati n

Centrosome

Rough endoplasmic reticulum Smooth endoplasmic reticulum

Ribosomes (small brwon dots) Central vacuole Tonoplast

Golgi apparatus

Microfilament s Intermediate filaments

CYTOSKELETO N

Microtubule s Mitochondrio n Peroxisom e Plasma membrane

Chloroplas t

Cell wall

Figure 6.9

Wall of adjacent cell

Plasmodesmat a

In plant cells but not animal cells: Chloroplasts Central vacuole and tonoplast Cell wall Plasmodesmata

Plant cells have some parts that animal cells don’t • Cell Wall • Central Vacuole • Plastids – Chloroplasts – Leukoplasts – chromoplasts

What animal cells have that plant cells don’t • Centrioles– function during cell division • Lysosomes – contain digestive enzymes

Cell Parts Organelles

Cellular Organelles – small, specialized structures in the

Surrounding the Cell

Cell Membrane • Outer membrane of cell that controls movement in and out of the cell • Double layer

Plasma Membrane The plasma membrane separates the living cell from its nonliving surroundings. This membrane: Is about 8 nm thick Surround the cell and controls traffic into and out of the cell Is selectively permeable, allowing some substances to cross more easily than others.

• Cell Membrane – Double layer of lipids (fats) that lets stuff in and out of cell

Membrane Structure The phospholipids and proteins in membranes create a unique physical environment, described by the fluid mosaic model. The membrane is a fluid structure with proteins embedded or attached to a double layer of phospholipids.

Fluid Model by Singer and Nicolson 1972 - SJ Singer and G.L Nicolson proposed the fluid mosaic model which accounted for the amphipathic characteristic of proteins.

Fluid mosaic model The membrane is a fluid structure with a “mosaic” of various proteins embedded in or attached to a double layer (bilayer) of phospholipids

Structure and Function of Organelles cell (plasma) membrane

• semi-permeable membrane which regulates the passage of substances into and out of the cell • composition: protein molecules dispersed throughout a double layer of lipid (fluid mosaic)

Factors affecting permeability of cell membrane to a particular substance: • 1. molecular size of the substance • 2. electrical charge on the atom or molecule of the substance • 3. solubility of the substance in water • 4. solubility of the substance in lipid

What determines the direction of the movement of molecules (diffusion) across the cell membrane?

• concentration of substances on each side of the membrane

Active transport requires energy. • A transport protein actively pumps a specific solute across a membrane against the solute’s concentration gradient; i.e., away from where the solute is less concentrated. Membrane proteins use ATP as their energy source for active transport.

Cell Wall • Most commonly found in plant cells & bacteria • Supports & protects cells

CELL WALL n

One of the feature of plant cells that distinguishes plants from animal cells.

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Found in prokaryotes, fungi, plants and some protists.

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Situated out of plasma membrane and not one of the component of protoplasm.

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Built by cellulose chain- where it is arranged in long fibril structure.

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Space between the fibril allows water, air and soluble molecules pass through the wall without any obstacle.

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A young plant cell first secretes relatively thin and flexible wall called primary cell wall.

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Between primary wall of adjacent cell is the middle lamella, a thin layer rich in sticky polysaccharides called pectin.

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The middle lamella glues the cells together.

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The sticky middle lamella cements the cell together.

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Plasmodesmata enables transportation in between cells.

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When the cell matures and stop growing, it strengthens its wall.

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Some plants cell do this simply by secreting hardening substance into the primary wall.

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Other cell add a secondary cell wall between the plasma membrane and the primary wall.

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The secondary wall, often deposited in several laminated layers, has a strong and durable matrix that affords the cell protection and support.

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Eg: Wood consist mainly of secondary wall

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The cytoplasm of one cell is continuous with the cytoplasm of its neighbours via plasmodesmata, channel through the walls.

Functions of the Cell Wall n

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The strong wall of the cells holds the plant to make it turgid The cell wall of plants: – Maintain the shape of the cells – Prevent excessive up take of water, mineral and ions

Cell Wall vs. Plasma Membrane

Cell Wall vs. Plasma Membrane

Cell Wall vs. Plasma Membrane

Cytoskeleton • Cell support • Anchors organelles • Transports materials • Helps cell move

Inside the Cell

Nucleus • Directs cell activities • Separated from cytoplasm by nuclear membrane • Contains genetic material - DNA

Eukaryotic Cell Organelles and Function •

Nucleus – Nickname: “The Control Center” – Function: holds the DNA – Parts: 1. Nucleolus: dark spot in the middle of the nucleus that helps make ribosomes

Nucleus • Control center of cell • Contains Chromosomes • Humans have 46 in each cell • Made of DNA - control heredity - control protein synthesis

• Surrounded by double membrane – nuclear membrane

• Cell Membrane

Nuclear Membrane • Surrounds nucleus • Made of two layers • Openings allow material to enter and leave nucleus

Nucleolus • Contains RNA to build proteins

Nucleolus • • • •

Within nucleus May be more than one Makes ribosomes Rich in RNA

Cytoplasm • Gel-like mixture • Surrounded by cell membrane • Contains hereditary material

Endoplasmic Reticulum • Moves materials around in cell • Smooth type: lacks ribosomes • Rough type (pictured): ribosomes embedded in surface

Eukaryotic Cell Organelles and Function •

Endoplasmic Reticulum (ER) – Nickname: “Roads” – Function: The internal delivery system of the cell

Endoplasmic Reticulum (ER) • Transports materials through the cytoplasm • There are two distinct regions of ER – Smooth ER, which lacks ribosomes – Rough ER, which contains ribosomes

Functions of Smooth ER 1. The Smooth ER – no ribosomes attached – Function: • • • •

Synthesizes fats or lipids Metabolizes carbohydrates Stores calcium Detoxifies poison, wastes

Functions of Rough ER 1. The Rough ER – have ribosomes attached » Rough appearance because it has ribosomes

– Function: • helps Produces proteins and membranes, that’s why it has ribosomes, which are distributed by transport vesicles • Transport proteins • Helps make membranes

Ribosomes • Each cell contains thousands • Found on ribosomes & floating throughout the cell

Ribosomes • Some are free, some are attached to endoplasmic reticulum. • Smallest organelles • Found in all cells, prokaryotic and eukaryotic

Ribosomes and Function •

Ribosomes – Function: makes proteins

Mitochondria and Function •

Mitochondria – Nickname: “The Powerhouse” – Function: Energy formation •

Breaks down food to make ATP – ATP: is the major fuel for all cell activities that require energy

Mitochondria • Produces energy through chemical reactions – breaking down fats & carbohydrates • Controls level of water and other materials in cell • Recycles and decomposes proteins, fats, and carbohydrates

Mitochondrion • Site of cellular respiration – food is broken down to release energy.

Golgi Bodies • Protein 'packaging plant' • Move materials within the cell • Move materials out of the cell

Golgi Complex and Function •

Golgi Complex – Nickname: The shippers – Function: packages, modifies, and transports materials to different location inside/outside of the cell – Appearance: stack of pancakes

Golgi Body • Packages cell secretions • Makes lysosomes – Contain digestive enzymes for breaking down food in food vacuoles and old, worn out structures – ex – sperm tail after fertilization.

Lysosome • Digestive 'plant' for proteins, fats, and carbohydrates • Transports undigested material to cell membrane for removal • Cell breaks down if lysosome explodes

Lysosomes and Function •

Lysosomes: circular, but bigger than ribosomes) – Nickname: “Clean-up Crews” – Function: to break down food into particles the rest of the cell can use and to destroy old cells

Chromosomes • In nucleus • Made of DNA • Contain instructions for traits & characteristics

Vacuoles • Membrane-bound sacs for storage, digestion, and waste removal • Contains water solution • Help plants maintain shape

Chloroplasts

Chloroplast • Usually found in plant cells • Contains green chlorophyll • Where photosynthesis takes place

Chloroplasts and Function •

Chloroplasts – Function: traps energy from the sun to produce food for the plant cell – Green in color because of chlorophyll, which is a green pigment

Structures used for Movement • Cilia

•Flagella

THE END