“Cells”Ch. 4

Cells

• Cells are small (Robert Hook)

• All plants are made of cells (Schleiden)

• All animals are made of cells (Schwann)

The Cell Theory

1. All living things are composed of cells

• Organisms can be categorized as single celled or multicellular

2. Cells are the basic unit of structure and function in living organisms.

3. All cells come from preexisting cells.• New cells arise from old cells

Why aren’t cells larger?

• Smaller cells function more efficiently!• The information from the DNA can be

relayed quickly • The rate at which exchange takes place

depends on the surface area of the cell, the total area of its cell membrane.

• The rate at which food and oxygen are used up and waste products are produced depends on the cell's volume.

Surface to Volume Ratio

Basic Cell Structure

• Cells range in size (They may be microscopic or as big as an ostrich egg.!!)

• All cells have 2 structures in common•Cell membrane- barrier that surrounds the cell•Cytoplasm- clear jelly like fluid that is within the cell.

The Plasma Membrane• All living cells are surrounded by a

plasma membrane• Basic Structure- Fluid Mosaic Model

• Lipid bilayer composed of phospholipids

• Head= Phosphate- polar (hydrophilic)

• Tail= Fatty acids- nonpolar (hydrophobic)

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Membrane Proteins• Another major component of the

membrane is a collection of membrane proteins• some proteins form channels

that span the membrane• these are called

transmembrane proteins

• other proteins are integrated into the structure of the membrane

• for example, cell surface proteins are attached to the outer surface of the membrane and act as markers

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Cell Types:Prokaryotes vs. Eukaryotes

Prokaryote•Smaller than eukaryotes•Contain a cell membrane and cytoplasm but lack a nucleus•Include single cell organism such as bacteria•Almost all bacteria have a cell wall. Some have a capsule that encloses the cell wall.

Eukaryote•Generally larger than prokaryotes•Contain a cell membrane, cytoplasm, nucleus, and organelles (specialized structures that perform specific activities within the cell)•Included some single-celled organisms and all multicellular organisms such as plants, animals, fungi, and protists.

Eukaryote•Generally larger than prokaryotes•Contain a cell membrane, cytoplasm, nucleus, and organelles (specialized structures that perform specific activities within the cell)•Included some single-celled organisms and all multicellular organisms such as plants, animals, fungi, and protists.

Prokaryotic Cells

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Eukaryotic Animal Cell

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Eukaryotic Plant Cell

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Nucleus• The nucleus is the

command and control center of the cell

• it also stores hereditary information

• The nuclear surface is bounded by a double-membrane called the nuclear envelope

• groups of proteins form openings called nuclear pores that permit proteins and RNA to pass in and out of the nucleus

Chromatin and Chromosomes

• Chromatin- granular tissue within the nucleus that’s composed of DNA and protein

• Chromosomes- condensed chromatin; visible during cell division

Organelles

• Found in the cytoplasm• Act like specialized organs within the

cell.• “little organs”

Ribosomes

• Responsible for the assembly of proteins

• Made of RNA and protein

• Translate information from the DNA

• Found on Rough Endoplasmic Reticulum

Endomembrane System

• Endoplasmic Reticulum• Golgi Complex• Lysosomes• Peroxisomes

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Endoplasmic Reticulum

• The region of the ER dedicated to protein synthesis is called the rough ER the rough spots are due to embedded ribosomes

• The region of the ER that aids in the manufacture of carbohydrates and lipids is called the smooth ER the surface of this region looks smooth because it

contains few to no embedded ribosomes

Rough and Smooth Endoplasmic Reticulum

Golgi Complex• Sometimes referred to as the Golgi Body or

Golgi Apparatus• Receives proteins produced by the rough ER.• Function in the collection, packaging, and

distribution of molecules manufactured in the cell.

• These proteins are modified with the attachment of carbohydrates and lipids

• “Packages and Ships the product”

Lysosomes

• The Golgi complex also gives rise to lysosomes these membrane-bounded structures contain

enzymes that break down macromolecules and old cell components• worn-out cell parts are broken down and their

components recycled to form new parts• particles that the cell has ingested are also digested

Peroxisomes

• Peroxisomes are vesicles that isolate certain types of chemical reactions

the reactions that are confined to these organelles function to

1. detoxify harmful by-products of metabolism

2. convert fats to carbohydrates in plants seeds for growth

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Organelle DNA

• DNA is the cells genetic information/ blue-prints.• DNA is ordinarily found in the nucleus.• There are two organelles that possess their own DNA

1. Mitochondria

2. Chloroplasts

Mitochondria

• “Power House”• Release energy stored in

food molecules to power growth, development, and movement within the cell.

• Found in plants and animal cells.

Chloroplasts• Found in plants and other photosynthetic organisms. (Not

found in animal and fungal cells)• Site of photosynthesis: process by which sunlight, Carbon

dioxide, and water are used to make carbohydrates and Oxygen

• Chlorophyll is the green pigment within the chloroplasts that give plants their color.

Centrioles

• Occur in pairs in the cytoplasm

• Contain a circular DNA molecule

• Anchor and assemble microtubules

• Function in cell division

Unique Plant Characteristics

• Plant cells have three structures present that are absent in animals cells• Cell Wall• Central Vacuole• Chloroplast

Cell Wall

• Protect and support the plant cell

• Composed of cellulose (polysaccharide)

Vacuole

• Sac-like structures within the cell that store water, salts, proteins, and carbohydrates.

• Plants have a large water vacuole that helps to support heavy structures

• Small vacuoles are called vesicles

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Theory of Endosymbiosis

• This theory proposes that some of today’s eukaryotic organelles evolved by a symbiosis in which one cell of a prokaryote species was engulfed by and lived inside another species of of prokaryote.

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Vacuoles

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Cilia and Flagella

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Cell Wall

• found in plants, fungi, and many protists

• comprised of different components than prokaryotic cell walls

• function in providing protection, maintaining cell shape, and preventing excessive water loss/uptake

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Cell Membrane

• The cell membrane takes in food and oxygen and eliminates wastes.

• Fluid Mosaic Model- Lipid Bilayer with proteins embedded throughout.

• The proteins may aid in the movement of molecules through the membrane.

• Selectively permeable the membrane allows some things to pass through and others cannot

Diffusion

• Terms to Review:• Solute- part of the solution that is being

dissolved• Solvent- part of the solution that is doing the

dissolving• Concentrations- amount of solute in a given

amount of solvent• Molecules are in constant random motion• Molecules tend to move from an area of high

concentration to an area of low concentration.• The process by which molecules move across

a cell membrane from high concentration to low concentration is known as Diffusion

Diffusion and Osmosis

• Movement of water and nutrients into a cell or elimination of wastes out of cell is is essential for survival

• This movement occurs across a biological membrane in one of three ways

• diffusion• membrane folding• through transport proteins

Diffusion

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Osmosis

• Osmosis- the diffusion of water

• Concentration Gradient- Water diffuses from an area of high concentration to an area of low concentration.

• Water will move until equilibrium is reached

The Effects of Osmosis on Cells

• Remember that water will move across the cell membrane until equilibrium is reached. At that point both sides of the membrane are isotonic.

• Prior to equilibrium, the side of the membrane with a higher solute concentration is “above strength” or hypertonic and the side with the lower solute concentration is “below strength” or hypotonic.

• Osmotic pressure is created by the diffusion of water. An animal cell placed in a hypotonic solution may burst due to this pressure. A plant cell placed in a hypotonic solution will no burse because they have a cell wall.

Osmosis in Animals Cells

Osmosis in Plant Cells

Bulk Passage

• Phagocytosis is endocytosis of particulate (solid) matter

• Pinocytosis is endocytosis of liquid matter

Exocytosis

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Facilitated Diffusion

Active Transport• Requires the input of energy

• utilizes protein channels that open only when energy is supplied

• energy is used to pump substances against or up their concentration gradients

• allows cells to maintain high or low concentration of certain molecules

• One of the most important channels that performs active transport in cells is the sodium-potassium pump

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