Eukaryotic CellsEukaryotic Cells

Eukaryotic organismsEukaryotic organisms

AlgaeAlgae ProtozoaProtozoa FungiFungi PlantsPlants AnimalsAnimals

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 ORGANELLESNON-MEMBRANE-BOUND ORGANELLES

– RIBOSOMES:RIBOSOMES:– CENTROSOMECENTROSOME

FLAGELLA AND CILIAFLAGELLA AND CILIA These are used for cellular locomotion or for These are used for cellular locomotion or for

moving substances along the surface of the moving substances along the surface of the cell. 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.

Flagella and CiliaFlagella and Cilia

Figure 4.23a, b

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.

Microtubules are made from Microtubules are made from tubulintubulin

9 pairs + 2 arrangements9 pairs + 2 arrangements

Figure 4.23c

CELL WALL and CELL WALL and GLYCOCALYXGLYCOCALYX

Most eukaryotic cells have cell walls, Most eukaryotic cells have cell walls, although they are much simple or although they are much simple or than those of prokaryotic cells. than those of prokaryotic cells.

Algae, fungi, and plants have Algae, fungi, and plants have cellulose in their cell wallscellulose in their cell walls

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

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.

Figure 4.22aPlasma membrane

Cell wall

Flagella with microtubules

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

prokaryotic cells is very similar in function and prokaryotic cells is very similar in function and structure. structure.

Eukaryotic membranes have different proteins, Eukaryotic membranes have different proteins, and also contain carbohydrates, which serve in and also contain carbohydrates, which serve in cell to cell recognition. cell to cell recognition. – Bacteria take advantage of these sites and attach there.Bacteria take advantage of these sites and attach there.

Eukaryotic plasma membranes also contain Eukaryotic plasma membranes also contain sterols, which are complex lipids not found in sterols, which are complex lipids not found in prokayriotic plasma membranes (with the prokayriotic plasma membranes (with the exception of exception of MycoplasmaMycoplasma).).– Sterols help the membranes resist lysis from increased Sterols help the membranes resist lysis from increased

osmotic pressure. osmotic pressure.

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.

White Blood Cell PseudopodWhite Blood Cell Pseudopod

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

the nucleus. the nucleus. Cytosol is the fluid portion of the cytoplasm. Cytosol is the fluid portion of the cytoplasm. 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 cell The movement of cytoplasm from one part of the cell to another to distribute nutrients is called to another to distribute nutrients is called cytoplasmic streaming.cytoplasmic streaming.

CYTOPLASMCYTOPLASM

Many of the important enzymes Many of the important enzymes found in the cytoplasmic fluid of found in the cytoplasmic fluid of prokaryotes is contained within prokaryotes is contained within organelles of eukaryotes.organelles of eukaryotes.

Some organelles are bound by a Some organelles are bound by a membrane and other organelles are membrane and other organelles are non-membrane bound.non-membrane bound.

MEMBRANE-BOUND MEMBRANE-BOUND ORGANELLESORGANELLES

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

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 channels called the nuclear envelope which has tiny channels (nuclear pores) which allow the nucleus to (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 wrap around the DNA and organize histones, which wrap around the DNA and organize it.it.

Figure 4.22a

Nucleus

Nucleolus

NucleusNucleus

Figure 4.24

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.

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.

Endoplasmic Endoplasmic ReticulumReticulum

Figure 4.25

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.

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.

Golgi ComplexGolgi Complex

Figure 2.8

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

modified into glycoproteins, glycolipids, modified into glycoproteins, glycolipids, and lipoproteins. and lipoproteins.

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

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.

VACUOLESVACUOLES

A space or cavity in the cytoplasm that is A space or cavity in the cytoplasm that is enclosed by a membrane. enclosed by a membrane.

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

– Temporary storage organelles for proteins, Temporary storage organelles for proteins, sugars, etc. sugars, etc.

– Store wastes and poisons to prevent toxicity to Store wastes and poisons to prevent toxicity to the cytoplasm. the cytoplasm.

– Take up water, enabling plant cells to increase Take up water, enabling plant cells to increase in size and also provide rigidity to leaves and in size and also provide rigidity to leaves and stems.stems.

VacuolesVacuoles

Figure 4.22b

MITOCHONDRIAMITOCHONDRIA

Rod-shaped organelles which appear Rod-shaped organelles which appear throughout the cytoplasm of most throughout the cytoplasm of most eukaryotic cells. eukaryotic cells.

There can be as many as 2000 There can be as many as 2000 mitochondria and one cell. mitochondria and one cell.

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

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

MitochondrionMitochondrion

Figure 4.27

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 enzyme that respiration, including the enzyme that makes ATP, are located on the cristae, and makes 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.

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.

EndosymbiotEndosymbiotic Theoryic Theory

Figure 10.2

CHLOROPLASTSCHLOROPLASTS

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

enzymes required for photosynthesis. enzymes required for photosynthesis. Contain ribosomes, DNA, and enzymes Contain ribosomes, DNA, and enzymes

involved in protein synthesis. involved in protein synthesis. 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.

ChloroplastChloroplast

Figure 4.28

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

NON-MEMBRANE-BOUND NON-MEMBRANE-BOUND ORGANELLESORGANELLES

RIBOSOMESRIBOSOMES CENTROSOMECENTROSOME

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 than They are larger (80S instead of 70S) and denser than

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

used inside the cell, and they do not have a used inside the cell, and they do not have a membrane. membrane.

The membrane-bound ribosomes are the ones The membrane-bound ribosomes are the ones attached to the rough ER. attached to the rough ER.

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

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

RibosomesRibosomes

Figure 4.19

Complete 80S Ribosome

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.

CentriolesCentrioles

Centrioles

CENTROSOMCENTROSOMEE

Figure 2.1

EUKARYOTIC PROKARYOTIC

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

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)