Eukaryotic CellsEukaryotic Cells

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Eukaryotic organismsEukaryotic organisms

AlgaeAlgae ProtozoaProtozoa FungiFungi PlantsPlants AnimalsAnimals

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Eukaryotic CellsEukaryotic Cells

FLAGELLA AND CILIAFLAGELLA AND CILIA CELL WALL and GLYCOCALYXCELL WALL and GLYCOCALYX PLASMA MEMBRANEPLASMA MEMBRANE CYTOPLASMCYTOPLASM MEMBRANE-BOUND ORGANELLESMEMBRANE-BOUND ORGANELLES NON-MEMBRANE-BOUND StructuresNON-MEMBRANE-BOUND Structures

– RIBOSOMESRIBOSOMES

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FLAGELLA AND CILIAFLAGELLA AND CILIA Flagella are used for cellular locomotionFlagella are used for cellular locomotion Cilia are used for locomotion or for moving Cilia are used for locomotion or for moving

substances along the surface of the cell. substances along the surface of the cell. Flagella are few and long. Algae of the genus Flagella are few and long. Algae of the genus

Euglena use a flagella for locomotionEuglena use a flagella for locomotion Cilia are more numerous and shorter. Protozoa Cilia are more numerous and shorter. Protozoa

use cilia for locomotion. use cilia for locomotion. – Ciliated cells of the human respiratory system move Ciliated cells of the human respiratory system move

mucous and debris along the surface of the cells in mucous and debris along the surface of the cells in the bronchial tubes and trachea to clear the lungs.the bronchial tubes and trachea to clear the lungs.

Prokaryotic flagella rotate, but the eukaryotic Prokaryotic flagella rotate, but the eukaryotic flagellum moves in a wavelike manner.flagellum moves in a wavelike manner.

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Flagella and CiliaFlagella and Cilia

Figure 4.23a, b55

MICROTUBULESMICROTUBULES

Both flagella and cilia are anchored Both flagella and cilia are anchored to the plasma membrane by a basal to the plasma membrane by a basal body, which consists of nine pairs of body, which consists of nine pairs of microtubules arranged in a ring, plus microtubules arranged in a ring, plus another two microtubules in the another two microtubules in the center of the ring, an arrangement center of the ring, an arrangement called a 9 + 2 array. called a 9 + 2 array.

Microtubules are made up of a Microtubules are made up of a protein called tubulin. protein called tubulin.

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Microtubules are made from Microtubules are made from tubulintubulin

9 pairs + 2 arrangements9 pairs + 2 arrangements

Figure 4.23c77

CELL WALL and CELL WALL and GLYCOCALYXGLYCOCALYX

Most non-animal eukaryotic cells (such as Most non-animal eukaryotic cells (such as plants) have cell walls, although they are plants) have cell walls, although they are much simpler than those of prokaryotic much simpler than those of prokaryotic cells. cells.

Algae, fungi, and plants have cellulose in Algae, fungi, and plants have cellulose in their cell walls instead of peptidoglycan.their cell walls instead of peptidoglycan.

Eukaryotic cells that lack a cell wall and Eukaryotic cells that lack a cell wall and have direct contact with the environment have direct contact with the environment may have a glycocalyx, which is a sticky may have a glycocalyx, which is a sticky carbohydrate. carbohydrate.

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CELL WALL and CELL WALL and GLYCOCALYXGLYCOCALYX

The glycolcalyx strengthens the cell The glycolcalyx strengthens the cell surface, helps attach cells together, surface, helps attach cells together, and contributes to cell-cell and contributes to cell-cell recognition. recognition.

Eukaryotic cells do not contain Eukaryotic cells do not contain peptidoglycan. peptidoglycan.

Antibiotics such as penicillins and Antibiotics such as penicillins and cephalosporins only act against cephalosporins only act against peptidoglycan and therefore do not peptidoglycan and therefore do not affect human eukaryotic cells. affect human eukaryotic cells.

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Figure 4.22aPlasma membrane

Cell wall

Flagella with microtubules

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PLASMA MEMBRANEPLASMA MEMBRANE The plasma membrane of eukaryotic and prokaryotic The plasma membrane of eukaryotic and prokaryotic

cells is very similar in function and structure. cells is very similar in function and structure. Eukaryotic membranes have different proteins, and Eukaryotic membranes have different proteins, and

also contain carbohydrates, which serve in cell to also contain carbohydrates, which serve in cell to cell recognition. cell recognition. – Bacteria take advantage of these sites and attach Bacteria take advantage of these sites and attach

there.there. Eukaryotic plasma membranes also contain sterols, Eukaryotic plasma membranes also contain sterols,

which are complex lipids not found in prokayriotic which are complex lipids not found in prokayriotic plasma membranes (with the exception of plasma membranes (with the exception of MycobateriaMycobateria).).– Sterols help the membranes resist lysis from Sterols help the membranes resist lysis from

increased osmotic pressure. increased osmotic pressure.

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PLASMA MEMBRANEPLASMA MEMBRANE

Substances can cross the plasma Substances can cross the plasma membrane by diffusion or active transport, membrane by diffusion or active transport, or a mechanism called endocytosis. or a mechanism called endocytosis.

This occurs when a segment of the plasma This occurs when a segment of the plasma membrane surrounds a particle, encloses membrane surrounds a particle, encloses it, and brings it into the cell. it, and brings it into the cell.

This process is called phagocytosis when This process is called phagocytosis when the plasma membrane projects a the plasma membrane projects a pseudopod (false foot), engulfs the pseudopod (false foot), engulfs the particle and brings it the cell. particle and brings it the cell.

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White Blood Cell PseudopodWhite Blood Cell Pseudopod

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CYTOPLASMCYTOPLASM Located inside the plasma membrane and outside Located inside the plasma membrane and outside

the nucleus. the nucleus. Only eukaryotic cytoplasm has a cytoskeleton:Only eukaryotic cytoplasm has a cytoskeleton:

– MicrofiamentsMicrofiaments– MicrotubulesMicrotubules

Cytoskeleton provides support and shape, and Cytoskeleton provides support and shape, and assists in transporting substances through the cell. assists in transporting substances through the cell.

They can also move the entire cell, as in They can also move the entire cell, as in phagocytosis. phagocytosis.

The movement of cytoplasm from one part of the The movement of cytoplasm from one part of the cell to another to distribute nutrients is called cell to another to distribute nutrients is called cytoplasmic streaming. cytoplasmic streaming. Cytoplasmic streaming video

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Cytoplasmic streaming videoCytoplasmic streaming video

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CYTOPLASMCYTOPLASM Many of the important enzymes found in Many of the important enzymes found in

prokaryotes float around freely in the prokaryotes float around freely in the cytoplasm. But in eukaryotes, the enzymes cytoplasm. But in eukaryotes, the enzymes are contained within organelles.are contained within organelles.

The definition of an organelle is “a The definition of an organelle is “a miniature organ that is bound by a miniature organ that is bound by a membrane”, similar to the plasma membrane”, similar to the plasma membrane. membrane.

Ribosomes are not organelles because they Ribosomes are not organelles because they do not have a membrane.do not have a membrane.

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MEMBRANE-BOUND MEMBRANE-BOUND ORGANELLESORGANELLES

– NUCLEUSNUCLEUS– ERER– GOLGI COMPLEXGOLGI COMPLEX– LYSOSOMESLYSOSOMES– VACUOLESVACUOLES– MITOCHONDRIAMITOCHONDRIA– CHLOROPLASTSCHLOROPLASTS– PEROXISOMESPEROXISOMES– CENTRIOLESCENTRIOLES

NOTE: Ribosomes are NOT membrane bound, so they are not organelles1717

NUCLEUSNUCLEUS Usually the largest structure in the cell.Usually the largest structure in the cell. Contains almost all of the cell’s hereditary Contains almost all of the cell’s hereditary

information (DNA). information (DNA). Some DNA is also found in mitochondria and in the Some DNA is also found in mitochondria and in the

chloroplasts of photosynthetic organisms. chloroplasts of photosynthetic organisms. The nucleus is surrounded by a double membrane The nucleus is surrounded by a double membrane

called the nuclear envelope which has tiny called the nuclear envelope which has tiny channels (nuclear pores) which allow the nucleus to channels (nuclear pores) which allow the nucleus to communicate with the cytoplasm. communicate with the cytoplasm.

Within the nucleus are one or more nucleoli which Within the nucleus are one or more nucleoli which are condensed regions of chromosomes where are condensed regions of chromosomes where ribosomal RNA is being synthesized. ribosomal RNA is being synthesized.

The nucleus also contains some proteins called The nucleus also contains some proteins called histones, which are like spools the DNA wraps histones, which are like spools the DNA wraps around to organize it.around to organize it.

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Figure 4.22a

Nucleus

Nucleolus

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NucleusNucleus

Figure 4.242020

Histones: Protein that DNA Histones: Protein that DNA wraps aroundwraps around

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NUCLEUSNUCLEUS Chromatin: a thread-like mass of dormant Chromatin: a thread-like mass of dormant

DNA.DNA. Chromatin shortens and thickens into Chromatin shortens and thickens into

chromosomes during replication. chromosomes during replication. Prokaryotic chromosomes do not undergo Prokaryotic chromosomes do not undergo

this process, do not have histones, and are this process, do not have histones, and are not enclosed in a nuclear envelope. not enclosed in a nuclear envelope.

Eukaryotic cells divide by mitosis and Eukaryotic cells divide by mitosis and meiosis; these processes do not occur in meiosis; these processes do not occur in prokaryotic cells. prokaryotic cells.

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Endoplasmic ReticulumEndoplasmic Reticulum

An extensive network of channels which An extensive network of channels which are continuous with the nuclear are continuous with the nuclear envelope. envelope.

Rough ERRough ER is studded with ribosomes, is studded with ribosomes, the sites of protein synthesis. the sites of protein synthesis.

Proteins synthesized by ribosomes that Proteins synthesized by ribosomes that are attached to rough ER enter the are attached to rough ER enter the channels within the ER to be processed channels within the ER to be processed and sorted. and sorted.

Thus, rough ER are protein factories.Thus, rough ER are protein factories.

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Endoplasmic Endoplasmic ReticulumReticulum

Figure 4.252424

Endoplasmic ReticulumEndoplasmic Reticulum

Smooth ERSmooth ER extends from the rough ER extends from the rough ER to form a separate network. to form a separate network.

Smooth ER does not have any ribosomes. Smooth ER does not have any ribosomes. It contains unique enzymes; it It contains unique enzymes; it

synthesizes phospholipids, fats, and synthesizes phospholipids, fats, and steroids such as estrogen and steroids such as estrogen and testosterone. testosterone.

In liver cells, the enzymes of smooth ER In liver cells, the enzymes of smooth ER detoxify drugs.detoxify drugs.

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GOLGI COMPLEXGOLGI COMPLEX Most of the proteins synthesized by Most of the proteins synthesized by

ribosomes from rough ER are transported ribosomes from rough ER are transported to other regions of the cell. to other regions of the cell.

The first step in the transport pathway is The first step in the transport pathway is through the Golgi complex. through the Golgi complex.

Proteins synthesized by ribosomes on the Proteins synthesized by ribosomes on the rough ER are surrounded by a portion of rough ER are surrounded by a portion of the ER membrane, which eventually buds the ER membrane, which eventually buds to form a transport vesicle. to form a transport vesicle.

This transport vesicle fuses with the This transport vesicle fuses with the Golgi complex, releasing the proteins Golgi complex, releasing the proteins into the channels of the Golgi complex. into the channels of the Golgi complex.

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Golgi ComplexGolgi Complex

Figure 2.82727

GOLGI COMPLEXGOLGI COMPLEX Within the Golgi complex, the proteins Within the Golgi complex, the proteins

are modified into glycoproteins and are modified into glycoproteins and lipoproteins. It also makes glycolipids. lipoproteins. It also makes glycolipids.

Some of the processed proteins leave the Some of the processed proteins leave the Golgi complex in secretory vesicles, Golgi complex in secretory vesicles, which detach from the Golgi membrane which detach from the Golgi membrane and deliver the proteins to the plasma and deliver the proteins to the plasma membrane, where they are discharged membrane, where they are discharged from the cell. from the cell.

Some of the processed proteins leave the Some of the processed proteins leave the Golgi complex in vesicles that are called Golgi complex in vesicles that are called storage vesicles. storage vesicles.

The major storage vesicle is a lysosome.The major storage vesicle is a lysosome.2828

LYSOSOMESLYSOSOMES Lysosomes are formed from the Golgi Lysosomes are formed from the Golgi

complexes and look like membrane-complexes and look like membrane-enclosed spheres. enclosed spheres.

Unlike mitochondria, lysosomes have only Unlike mitochondria, lysosomes have only one membrane and lack internal structure. one membrane and lack internal structure.

They contain as many as 40 different They contain as many as 40 different kinds of powerful digestive enzymes kinds of powerful digestive enzymes capable of breaking down various capable of breaking down various molecules. molecules.

They can also digest bacteria that enter They can also digest bacteria that enter the cell. Human white blood cells, which the cell. Human white blood cells, which use phagocytosis to ingest bacteria, use phagocytosis to ingest bacteria, contain large numbers of lysosomes.contain large numbers of lysosomes.

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VACUOLES/VESICLESVACUOLES/VESICLES

A vesicle is a small container and a A vesicle is a small container and a vacuole is a larger container. Both of them vacuole is a larger container. Both of them are just spheres surrounded by a are just spheres surrounded by a membrane.membrane.

Made by the Golgi complexMade by the Golgi complex Functions:Functions:

– Storage for nutrients such as proteins, lipids, sugars, water

– Store wastes and poisons to prevent toxicity to the cytoplasm

– Used to transport substances within a cell and transport substances to the outside of the cell

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VacuolesVacuoles

Figure 4.22b3131

MITOCHONDRIAMITOCHONDRIA Rod-shaped organelles which appear Rod-shaped organelles which appear

throughout the cytoplasm of most eukaryotic throughout the cytoplasm of most eukaryotic cells. cells.

They make most of the cell’s ATP.They make most of the cell’s ATP. There can be as many as 2000 mitochondria in There can be as many as 2000 mitochondria in

one cell. one cell. Mitochondria have a double membrane; the Mitochondria have a double membrane; the

outer membrane is smooth but the inner outer membrane is smooth but the inner membrane is arranged in a series of folds membrane is arranged in a series of folds called cristae. called cristae.

The center of the mitochondrion is a semi-fluid The center of the mitochondrion is a semi-fluid substance called the matrix. substance called the matrix.

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MitochondrionMitochondrion

Figure 4.273333

MITOCHONDRIAMITOCHONDRIA

The convolutions of the cristae provide an The convolutions of the cristae provide an enormous surface area on which chemical enormous surface area on which chemical reactions can occur. reactions can occur.

Some proteins that function in cellular Some proteins that function in cellular respiration, including the enzymes that respiration, including the enzymes that make ATP, are located on the cristae, and make ATP, are located on the cristae, and many of the metabolic steps involved in many of the metabolic steps involved in cellular respiration occur in the matrix. cellular respiration occur in the matrix.

Mitochondria are called the powerhouses Mitochondria are called the powerhouses of the cell because of their central role in of the cell because of their central role in ATP production. ATP production.

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MITOCHONDRIAMITOCHONDRIA

Mitochondria contain their own Mitochondria contain their own ribosomes and DNA and are able to ribosomes and DNA and are able to replicate themselves and make replicate themselves and make their own proteins. their own proteins.

It is theorized that they have It is theorized that they have evolved from bacteria millions of evolved from bacteria millions of years ago, which have a symbiotic years ago, which have a symbiotic relationship within the organism.relationship within the organism.

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EndosymbiotEndosymbiotic Theoryic Theory

Figure 10.23636

CHLOROPLASTSCHLOROPLASTS

Only found in algae and green plants.Only found in algae and green plants. Contains the pigment chlorophyll Contains the pigment chlorophyll

plus enzymes required for plus enzymes required for photosynthesis. photosynthesis.

Capable of multiplying on their own Capable of multiplying on their own within the cell. within the cell.

Chloroplasts and mitochondria Chloroplasts and mitochondria replicate by binary fission like replicate by binary fission like bacteria.bacteria.

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ChloroplastChloroplast

Figure 4.283838

PEROXISOMESPEROXISOMES Similar to lysosomes but they are smallerSimilar to lysosomes but they are smaller Contain one or more enzymes that can Contain one or more enzymes that can

oxidize various substances including oxidize various substances including alcohol. alcohol.

The end product of the oxidation reaction is The end product of the oxidation reaction is hydrogen peroxide (Hhydrogen peroxide (H22OO22), which is a very ), which is a very toxic compound. toxic compound.

However peroxisomes also contain the However peroxisomes also contain the enzyme catalase, which decomposes enzyme catalase, which decomposes hydrogen peroxide, so it is safe within the hydrogen peroxide, so it is safe within the cell. cell.

Peroxisomes can also be used to digest Peroxisomes can also be used to digest bacteria that have invaded the cell.bacteria that have invaded the cell.

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CENTROSOMECENTROSOME

Located near the nucleus. Located near the nucleus. It consists of proteins fibers and two centrioles, It consists of proteins fibers and two centrioles,

which are cylinders of small fibers. which are cylinders of small fibers. They organize the spindles that appear during They organize the spindles that appear during

mitosis to help the duplicated chromosomes mitosis to help the duplicated chromosomes move towards opposite ends of the cell. move towards opposite ends of the cell.

Each of the two centrioles in the centrosome is Each of the two centrioles in the centrosome is arranged so that the long axis of one centriole arranged so that the long axis of one centriole is at a right angle to the long axis of the other.is at a right angle to the long axis of the other.

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Centrioles of the Centrioles of the CentrosomeCentrosome

Centrioles

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CENTROSOMCENTROSOMEE

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NON-MEMBRANE-BOUND NON-MEMBRANE-BOUND StructuresStructures

RIBOSOMESRIBOSOMES– We cannot call these “organelles” We cannot call these “organelles”

because they do not have a because they do not have a membrane around them.membrane around them.

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RIBOSOMESRIBOSOMES Attached to the outer surface of rough ER are Attached to the outer surface of rough ER are

ribosomes or floating free in the cytoplasm. ribosomes or floating free in the cytoplasm. They are the sites of protein synthesis in the cell. They are the sites of protein synthesis in the cell. They are larger (80S instead of 70S) and denser They are larger (80S instead of 70S) and denser

than the ribosomes of prokaryotic cells. than the ribosomes of prokaryotic cells. The free ribosomes synthesize proteins which are The free ribosomes synthesize proteins which are

used inside the cell. used inside the cell. The ribosomes that are attached to the rough ER The ribosomes that are attached to the rough ER

synthesize proteins destined for insertion in the synthesize proteins destined for insertion in the plasma membrane or for export from the cell. plasma membrane or for export from the cell.

Ribosomes within the mitochondria synthesize Ribosomes within the mitochondria synthesize special mitochondrial proteins.special mitochondrial proteins.

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RibosomesRibosomes

Figure 4.19

Complete 80S Ribosome

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Figure 2.14646

PROKARYOTIC EUKARYOTIC

One circular chromosome, not membrane-bound

Paired chromosomes, membrane-bound

No histones Histones present

No organelles Organelles present: Golgi complex, ER, mitochondria, chloroplasts

Peptidoglycan cell walls Polysaccharide cell walls

Reproduce by binary fission Reproduce by mitosis/meosis

No true nucleus; no nuclear membrane True nucleus; nuclear membrane; also has nucleoli

Glycocalyx present as capsule or slime layer

Present in some cells that lack a cell wall

Plasma membrane has no carbohydrates and lack sterols

Plasma membrane has carbohydrates and sterols

No cytoskeleton Has a cytoskeleton

Ribosomes are small (70S) Ribosomes are large (80S)47