1. Eucaryotic Cell Structure and Function
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Chapter 4
Eucaryotic Cell Structure and Function

2. An Overview of Eucaryotic Cell Structure
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An Overview of Eucaryotic Cell Structure
membrane-delimited nuclei
membrane-bound organelles that perform specific functions
more structurally complex than procaryotic cell
generally larger than procaryotic cell

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Table 4.1

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AV= autophagic vacuole; C=centriole; Ch=chloroplast; CI=cilium; CR=chromatin; DV=digestion vacuole; F=microfilaments; G=glycogen; GA=Golgi apparatus; GE=GERL; LD=lipid droplet; M=mitochondrion; MT=microtubules; N=nucleus; NU=nucleolus; P=peroxisome; PL=primary lysosome; PM=plasma membrane; PV=pinocytotic vesicle; R=ribosomes and polysomes; RB=residual body; RER=rough endoplasmic reticulum; SER=smooth endoplasmic reticulum; SV=secretion vacuole
Figure 4.1

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AV= autophagic vacuole; C=centriole; Ch=chloroplast; CI=cilium; CR=chromatin; DV=digestion vacuole; F=microfilaments; G=glycogen; GA=Golgi apparatus; GE=GERL; LD=lipid droplet; M=mitochondrion; MT=microtubules; N=nucleus; NU=nucleolus; P=peroxisome; PL=primary lysosome; PM=plasma membrane; PV=pinocytotic vesicle; R=ribosomes and polysomes; RB=residual body; RER=rough endoplasmic reticulum; SER=smooth endoplasmic reticulum; SV=secretion vacuole
Figure 4.2

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AV= autophagic vacuole; C=centriole; Ch=chloroplast; CI=cilium; CR=chromatin; DV=digestion vacuole; F=microfilaments; G=glycogen; GA=Golgi apparatus; GE=GERL; LD=lipid droplet; M=mitochondrion; MT=microtubules; N=nucleus; NU=nucleolus; P=peroxisome; PL=primary lysosome; PM=plasma membrane; PV=pinocytotic vesicle; R=ribosomes and polysomes; RB=residual body; RER=rough endoplasmic reticulum; SER=smooth endoplasmic reticulum; SV=secretion vacuole
Figure 4.3

7. The Plasma Membrane and Membrane Structure
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The Plasma Membrane and Membrane Structure
the fluid mosaic model is based on eucaryotic membranes
major membrane lipids include phosphoglycerides, sphingolipids and cholesterol

8. The Plasma Membrane and Membrane Structure
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The Plasma Membrane and Membrane Structure
eucaryotic membranes contain microdomains called lipid rafts
They are enriched for certain lipids and proteins
They participate in a variety of cell processes such as cell movement and transduction

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Figure 4.4

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The Cytoplasmic Matrix, Microfilaments, Intermediate Filaments, and Microtubules
The many organelles of eucaryotic cells lie in the cytoplasmic matrix
Cytoskeleton
vast network of interconnected filaments within the cytoplasmic matrix
Filaments that form the cytoskeleton: microfilaments, microtubules, and intermediate filaments
plays role in both cell shape and cell movement

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Figure 4.5

12. Microfilaments minute protein filaments, 4 to 7 nm in diameter
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Microfilaments
minute protein filaments, 4 to 7 nm in diameter
scattered within cytoplasmic matrix or organized into networks and parallel arrays
composed of actin protein
involved in cell motion and shape changes

13. Microtubules shaped like thin cylinders ~ 25 nm in diameter
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Microtubules
shaped like thin cylinders ~ 25 nm in diameter
help maintain cell shape
involved with microfilaments in cell movements
participate in intracellular transport processes

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Figure 4.6

15. Intermediate Filaments
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Intermediate Filaments
heterogeneous elements of the cytoskeleton
~10 nm in diameter
role in cell is unclear
Some shown to form nuclear lamina
Others help link cells together to form tissues

16. The Endoplasmic Reticulum
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The Endoplasmic Reticulum
irregular network of branching and fusing membranous tubules and flattened sacs (cisternae – s., cisterna)
Figure 4.7

17. Two types of Endoplasmic Reticulum (ER)
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Two types of Endoplasmic Reticulum (ER)
rough ER
ribosomes attached
synthesis of secreted proteins by ER-associated ribosomes
smooth ER
devoid of ribosomes
synthesis of lipids by ER-associated enzymes

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Functions of ER
transports proteins, lipids, and other materials within cell
major site of cell membrane synthesis
synthesis of lysosomes

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The Golgi Apparatus
membranous organelle made of cisternae stacked on each other
dictyosomes
stacks of cisternae
involved in modification, packaging, and secretion of materials
Figure 4.8 (a)

20. cis face associated with ER
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movement of materials
Figure 4.8 (b)
cis face associated with ER

21. Lysosomes membrane-bound vesicles found in most eucaryotes
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Lysosomes
membrane-bound vesicles found in most eucaryotes
involved in intracellular digestion
contain hydrolases, enzymes which hydrolyze molecules and function best under slightly acidic conditions
maintain an acidic environment by pumping protons into their interior

22. The Biosynthetic-Secretory Pathway
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The Biosynthetic-Secretory Pathway
used to move materials to lysosomes as well as from the inside of the cell to either the cell membrane or cell exterior
proteins synthesized by ribosomes on rough ER released in small vesicles  cis face of Golgi apparatus trans face of Golgi apparatus
transport vesicles released from trans face of Golgi

23. The Biosynthetic-Secretory Pathway (continued)
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The Biosynthetic-Secretory Pathway (continued)
after release some vesicles deliver their contents to lysosomes while others deliver to cell membrane
quality assurance mechanism
Unfolded or misfolded proteins are secreted into cytosol, targeted for destruction by ubiquitin polypeptides.
proteasomes destroy targeted proteins

24. Proteasome Degradation of Proteins
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Proteasome Degradation of Proteins
Figure 4.9 (a)

25. Proteasome Degradation of Proteins
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Proteasome Degradation of Proteins
Figure 4.9 (b)

26. The Endocytic Pathway endocytosis
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The Endocytic Pathway
endocytosis
used to bring materials into the cell
solutes or particles taken up and enclosed in vesicles pinched from plasma membrane
in most cases materials are then delivered to lysosome and destroyed

27. Types of Endocytosis phagocytosis clathrin-dependent endocytosis
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Types of Endocytosis
phagocytosis
Use of cell surface protrusions to surround and engulf particles
Resulting vesicles called phagosomes
clathrin-dependent endocytosis
involves membrane regions coated on cytoplasmic side with the protein clathrin (coated pits)
coated pits have external receptors that specifically bind macromolecules
pinching off of coated pits forms coated vesicles
called receptor-mediated endocytosis

28. More Types of Endocytosis
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More Types of Endocytosis
caveolae–dependent endocytosis
enriched in cholesterol and the membrane protein caveolin
When caveolae pinch off membrane are called caveolar vesicles
do not deliver their contents to lysosomes
may play role in signal transduction, transport of small as well as macromolecules

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Autophagy
Delivery of materials to be digested by route that does not involve endocytosis
Involves digestion and recycling of cytoplasmic components
Double membrane (may be from endoplasmic reticulum) surrounds cell component forming an autophagosome
Autophagosome fuses with late endosome which ultimately becomes a lysosome

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Figure 4.10

31. Once Lysosome is formed…
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Once Lysosome is formed…
digestion occurs without release of lysosome enzymes into cytoplasmic matrix
as contents are digested, products leave lysosome and can be used as nutrients
resulting lysosome called a residual body which can release contents to cell exterior by process called lysosome secretion

32. Eucaryotic Ribosomes 80S in size
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Eucaryotic Ribosomes
80S in size
60S + 40S subunits
may be attached to ER or free in cytoplasmic matrix
Figure 4.3

33. Eucaryotic ribosomes…
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Eucaryotic ribosomes…
Proteins made on ribosomes of RER are often secreted or inserted into ER membrane as integral membrane proteins
Free ribosomes synthesize nonsecretory and nonmembrane proteins
Some proteins are inserted into organelles

34. Mitochondria site of tricarboxylic acid cycle activity
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Mitochondria
site of tricarboxylic acid cycle activity
site where ATP is generated by electron transport and oxidative phosphorylation
Figure 4.3

35. Mitochondrial structure
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Mitochondrial structure
outer membrane
contains porins similar to the outer membrane of gram negative bacteria
inner membrane
highly folded to form cristae (s., crista)
location of enzymes and electron carriers for electron transport and oxidative phosphorylation

36. Mitochondrial structure…
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Mitochondrial structure…
matrix
contains ribosomes, mitochondrial DNA, and large calcium phosphate granules
contains enzymes of the tricarboxylic acid cycle and enzymes involved in catabolism of fatty acids

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Figure 4.11

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Figure 4.12

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Figure 4.13

40. Chloroplasts type of plastid site of photosynthetic reactions
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Chloroplasts
type of plastid
pigment-containing organelles observed in plants and algae
site of photosynthetic reactions
surrounded by double membrane
Figure 4.3

41. Chloroplast structure
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Chloroplast structure
the stroma (a matrix) is within inner membrane
contains DNA, ribosomes, lipid droplets, starch granules, and thylakoids
thylakoids
flattened, membrane-delimited sacs
grana (s., granum) – stacks of thylakoids
site of light reactions (trapping of light energy to generate ATP, NADPH, and oxygen)

42. Chloroplast structure
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Chloroplast structure
stroma is site of dark reactions of photosynthesis (formation of carbohydrates from water and carbon dioxide)
algal chloroplasts many contain a pyrenoid
participates in polysaccharide synthesis

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Figure 4.14

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Figure 4.15

45. The Nucleus and Cell Division
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The Nucleus and Cell Division
nucleus
membrane-bound structure that houses genetic material of eucaryotic cell
Figure 4.3

46. Nuclear structure chromatin dense fibrous material within nucleus
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Nuclear structure
chromatin
dense fibrous material within nucleus
contains DNA
condenses to form chromosomes during cell division

47. Nuclear structure… nuclear envelope
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Nuclear structure…
nuclear envelope
double membrane structure that delimits nucleus
penetrated by nuclear pores
pores allow materials to be transported into or out of nucleus

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freeze-etch preparation of the conidium of the fungus Geotrichous candidum; note large convex nuclear surface with nuclear pores scattered over it
Figure 4.15

49. The Nucleolus  1 nucleolus/nucleus not membrane enclosed
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The Nucleolus
 1 nucleolus/nucleus
not membrane enclosed
important in ribosome synthesis
directs synthesis and processing of rRNA
directs assembly of rRNA and ribosomal proteins to form ribosomes

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Figure 4.16

51. Mitosis and Meiosis mitosis one component of cell cycle
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Mitosis and Meiosis
mitosis
one component of cell cycle
distributes DNA to 2 new nuclei
ploidy (number of chromosomes) of progeny cells is the same as the parent
thus, after mitosis, a diploid organism remains diploid

52. preparation for mitosis
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period of cell growth
preparation for mitosis
synthesis of RNA, ribosomes, and cytoplasmic
constituents
Figure 4.17

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Figure 4.18

54. Mitosis and Meiosis… meiosis
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Mitosis and Meiosis…
meiosis
complex, two-stage process of nuclear division
number of chromosomes in the resulting progeny cells is reduced by ½
diploid  haploid

55. Figure 4.19 generalized eucaryotic life cycle
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generalized eucaryotic life cycle
Figure 4.19

56. External Cell Covering
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External Cell Covering
cell wall
rigid variable make-up
algae – cellulose and pectin
diatoms – silica
fungi – chitin, cellulose, and glucan

57. External Cell Covering
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External Cell Covering
pellicle
relatively rigid layer of components just beneath plasma membrane
common in protozoa
not as strong or rigid as cell wall
provides characteristic shape to cell

58. Cilia and Flagella cilia (s., cilium) flagella (s., flagellum)
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Cilia and Flagella
cilia (s., cilium)
5-20 μm long
beat with two phases, working like oars
flagella (s., flagellum)
μm long
move in undulating fashion

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Figure 4.20

60. Structure of flagella and cilia
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Structure of flagella and cilia
membrane-bound cylinders ~ 2 μm in diameter
axoneme
set of microtubules in a arrangement
basal body
at base of flagellum or cilium
directs synthesis of flagella and cilia

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Figure 4.21

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Figure 4.23

63. Comparison of Procaryotic and Eucaryotic Cells
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Comparison of Procaryotic and Eucaryotic Cells
Figure 4.24

64. Comparison of Procaryotic and Eucaryotic Cells
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Comparison of Procaryotic and Eucaryotic Cells
Table 4.2

65. The molecular unity of procaryotes and eucaryotes
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The molecular unity of procaryotes and eucaryotes
same basic chemical composition
same genetic code
same basic metabolic processes