Lecture 3 and 4- Eukaryotic cells Flashcards
Compartmentalisation of eukaryotic cells, functions and major components (181 cards)
1
Q
What are organelles?
A
Membraneous compartments and other structures that lack membranes but possess distinctive shapes and functions (such as ribosomes)
2
Q
What defines the roles of different organelles?
A
The chemical reactions that they can carry out
3
Q
What are the three main features of the nucleus?
A
It contains most of the cell’s DNA
It replicates genetic material
Site of the 1st steps in decoding genetic information
Site of genetic control of the cells activities
Assembly of ribosomes
4
Q
What are the general functions of the mitochondria?
A
Power house of the cell
Energy stored in the bonds of carbohydrates and fatty acids is converted into a more useful form, ATP
5
Q
What are lysosomes and vacuoles?
A
Cellular digestive systems in which large molecules are hydrolyzed into usable monomers
6
Q
What are two purposes of membranes surrounding organelles?
A
- Keep organelle’s molecules away from other molecules in the cell
- Regulates the movement of raw materials and products into and out of the organelle
7
Q
Why was the development of membrane bound organelles important in eukaryotic cells?
A
It gives the ability for eukaryotic cells to specialise and hence form organs and tissues of a complex, multicellular body
8
Q
What can stains tell us about organelles?
A
Their chemical composition
9
Q
Explain, in 4 points, the process of cell fractionation.
A
- Homogenize tissue in grinder (destroys plasma membrane)
- Cell homegenate contains large and small organelles
- Centrifuge to separate based on size or density
- Heaviest components sink to the bottom
10
Q
How is information stored within a cell?
A
In a sequence of nucleotides in DNA molecules.
Most DNA resides in the nucleus
11
Q
What organelle is usually the largest organelle in a eukaryotic cell?
A
The nucleus
12
Q
What is the approximate diameter of a nucleus?
A
5 micrometers
13
Q
What occurs in the nucleolus?
A
The assembly of ribosomes from RNA and specific proteins
14
Q
What is nucleus surrounded by?
A
Two membranes that form the nuclear envelope
15
Q
By what distance are the nuclear membranes separated by?
A
10-20nm
16
Q
How many nuclear pores are there on a nucleus?
A
3500
17
Q
What is the function of nuclear pores?
A
To connect the interior of the nucleus with the cytoplasm
18
Q
What is the structure of the nuclear pores?
A
- Composed of 100 different proteins interacting hydrophobically
- Each pore is surrounded by a pore complex
19
Q
What is the structure of a pore complex?
A
8 large protein aggregates arranged in an octagon surrounding the nuclear pore.
20
Q
What is a nuclear basket?
A
Protein fibrils on the nuclear side form a basket like structure
21
Q
How do molecules pass through nuclear pores?
A
Molecules less than 10,000 daltons freely diffuse
Molecules up to 50,000 daltons diffuse slowly
Larger molecules require a short amino acid sequence called a nuclear localisation signal
22
Q
What evidence is there for the nuclear localisation signal?
A
- The sequence appears in nuclear proteins but not proteins that remain in the cytoplasm
- If removed, the protein remains in the cytoplasm
- If added to a protein, it enters the cytoplasm
- Some viruses have the signal sequence and enter the cytoplasm, others do not.
23
Q
How does a signal sequence result in passage through a nuclear pore?
A
Three-dimensional structure binds noncovalently to a protein receptor
The receptor changes shape so the pore stretches and the protein passes through
24
Q
What organelle is the nuclear envelope continuous with?
A
The endoplasmic reticulum
25
What is the name of the fibrous complex that occurs when DNA combines with a protein?
Chromatin
26
What does chromatin aggregate into before cell division?
chromosomes
27
What surrounds chromatin?
Water and dissolved substances called the nucleoplasm
28
What organises the chromatin?
The nuclear matrix (structural proteins)
29
What is chromatin attached to at the edge of the nucleus?
The nuclear lamina- formed from lamins into filaments
30
What is the purpose of the lamina?
Maintain the shape of the nucleus by attaching to the nuclear envelope and chromatin
31
Where are ribosomes found within prokaryotic cells?
Free floating
32
Where are ribosomes found within eukaryotic cells?
The cytoplasm- free or attached to the endoplasmic reticulum,
and inside the mitochondria and chloroplasts
33
What are ribosomes?
The sites where proteins are synthesised under the direction of the nucleic acids
34
How are eukaryotic and prokaryotic ribosomes similar?
They are made up of two different-sized subunits
35
What type of molecule are ribosomes made up of?
ribosomal RNA bound noncovalently to 50 proteins
36
What are the components of the endomembrane system?
The endoplasmic reticulum, golgi body, lysosomes, vesicles, nucleus
37
How large is the endomembrane system?
Much of the volume of the cell is taken up by this system
38
What is the endomembrane system?
A group of interrelated organelles
39
How is the endoplasmic reticulum viewed?
Through an electron mircograph
40
What is the structure of the endoplasmic reticulum?
A network of interconnected membranes braching through the cytoplasm forming tubes and flattened sacs
41
What is the lumen?
The interior of the endoplasmic reticulum
42
How much of the volume of the cell can the ER enclose?
Up to 10%
43
What is the rough endoplasmic reticulum?
The ER that is studded with ribosomes that are temporarily attatched
44
What are the functions of the rough ER?
- Segregates certain newly synthesised proteins and transports them to other locations within the cell
- Inside, proteins can be chemically modified so alter function/destination
45
What do the ribosomes attached to the ER do?
Synthesize proteins that function outside of the cytosol (proteins transported out of cell, or into membrane or endomembrane system)
46
Where do proteins synthesized by ribosomes attached to the ER go after they are synthesized?
Into the lumen of the ER
47
How do proteins enter the ER after being synthesized by ribosomes on its surface?
A sequence of amino acids on the protein act as an RER localisation signal
48
What happens to proteins after they have entered the RER?
They undergo changes- including: tertiary folding and formation of disulfide bridges
49
What type of molecule do proteins become after gaining carbohydrate groups in the RER?
Glycoproteins- these can act as an addressing system in lysosomes
50
What is the structure of the smooth endoplasmic reticulum?
```
More tubular (less like flattened sacs)
Lack ribosomes
```
51
What happens to proteins that were synthesized in the RER inside the lumen of the SER?
They are chemically modified
52
What are the three main roles of the SER?
- Chemically modifying small molecules taken in by the cell (drugs, pesticides)
- Site of hydrolysis of glycogen in animal cells
- Site of lipid and steroid synthesis
53
What do cells that synthesize a lot of proteins have lots of?
Endoplasmic reticulum
54
Give examples of cells with many endoplasmic reticulum
Glandular cells- secrete digestive enzymes
| White blood cells- secrete antibodies
55
What type of cell has many smooth endoplasmic reticulum?
Liver cells- these modify molecules that enter the body from the digestive system
56
What is the shape of the Golgi apparatus?
Flattened membranous stacks piled like saucers with small membrane-enclosed vesicles
57
What are the name of the membranous sacs that make up the golgi apparatus?
Cisternae
58
How long is the golgi apparatus?
1 micrometer
59
What are the three main roles of the golgi apparatus?
- Receive proteins from ER and further modify them
- Concentrate, package and sort proteins before sending (cellular or extracellular)
- Synthesis of some polysaccharides in the plant wall
60
Where is the golgi apparatus in plants, protists, fungi and many invertebrates within the cell?
Scattered throughout the cytoplasm
61
How is the golgi apparatus differently arranged in vertebrate cells?
Fewer stacks form larger, single, more complex golgi body
62
What are the three functionally distinct parts of the golgi body?
Bottom
Middle
Top
63
What does the bottom cisternae of the golgi apparatus lie closest to and what region is it?
Closest to nucleus/patch of RER
| The cis region
64
What does the middle cisternae of the golgi apparatus make up?
The medial region
65
What does the top cisternae of the golgi apparatus lie closest to and what region is it in?
Lies closest to the surface of the cell
| The trans region
66
How are the three parts of the golgi apparatus different?
They contain different enzymes and perform different functions
67
How do proteins remain segregated from the cytoplasm from the ER to the golgi apparatus?
The ER buds off a membranous vesicle containing the protein
68
What happens once a vesicle reaches the golgi apparatus?
The membranes fuse and releases protein
69
Where do vesicles that bud off of the trans regions go?
Carry their contents away from the golgi apparatus
70
Where do lysosomes originate from?
The golgi apparatus
71
What do lysosomes contain?
Digestive enzymes
72
What are lysosomes the site of?
Macromolecules (proteins, polysaccharides, nucleic acids, lipids) are hydrolysed into their monomers
73
How big are lysosomes?
1 micometer in diameter
74
How many lysosomes are their in a cell?
Dozens, depending on needs
75
How do food and foreign objects enter the cell?
Phagocytosis- pocket that forms in membrane is called phagosome
76
What is the function of lysosomes?
Site of break down of food and foreign objects
77
How does the lysosome digest a phagosome?
The primary lysosome fuses its membrane with the phagosome. This forms a secondary lysosome in which digestion occurs.
78
What makes the secondary lysosome break down its contents?
- Digestive enzymes
| - Slightly more acidic environment
79
What happens to the products of lysosome break down?
They diffuse through the lysosome membrane and provide raw materials for other cell processes
80
What happens after a secondary lysosome is finished?
It fuses with the plasma membrane and releases undigested contents into the environment
81
What is the process by which lysosomes digest the cells own materials?
Autophagy
82
What cells don't have lysosomes?
Plant cells- the vacuole may function equivalently
83
What do cells use energy for?
Growth, reproduction, movement
84
Where does the break down of fuel molecules start in eukaryotic cells?
The cytosol
85
Where do partially degraded molecules enter?
The mitochondria
86
What is the main function of the mitochondria?
Convert potential chemical energy of fuel molecules into a form the cell can use (ATP)
87
What is cellular respiration?
The process of converting fuel molecules and oxygen into ATP
88
What is the diameter and length of mitochondria?
1.5 micrometers diameter
| 2-8 micrometers long
89
How many mitochondria are there in cells?
```
One (some unicellular protists)
Hundred thousand (large egg cells)
```
Typical humans liver cell- more than 1000
90
How many membranes do mitochondria have?
2- the outer and inner
91
What does the outer membrane of the mitochondria do?
Smooth and protective
| Offers little resistance to movement of substances in and out
92
What is the structure of the inner membrane of the mitochondria?
Folds inwards in many places (larger surface area)
| Folds--> regular shelf like structures called cristae
93
What is embedded in the folds of the inner mitochondrial membrane?
Large protein complexes involved in cellular respiration
94
What space is enclosed by inner and outer mitochondrial membranes?
The mitochondrial matrix
95
What does the mitochondrial matrix contain?
Enzymes
| Ribosomes and DNA to make proteins needed for cellular respiration
96
What are plastids?
```
A class of organelles
Found only in plants and certain protists
```
97
What is chloroplast?
A type of plastid
Contains green pigment chlorophyll
Site of photosynthesis
98
What happens during photosynthesis?
Light energy is converted into chemical energy of bonds between atoms
99
What is the purpose of photosynthetic products?
Provide food for photosynthetic organisms and the organisms that eat them
100
What is the structure of a chloroplast?
Variable size/shape
Two membranes
Internal membranes that differ among organisms
101
What do the internal membranes of chloroplasts look like?
Stacks of flat, hollow pita bread called grana
102
What do grana consist of?
A series of flat, closely packed circular compartments called thylakoids
103
What do thylakoid membranes contain?
Phospholipids
Proteins
Light harvesting pigments
104
How are thylakoids connected?
Thlakoids of one granum are connected to those of other grana (membrane network)
105
What is the fluid surrounding grana?
Stroma
106
What is in the stroma?
Ribosomes and DNA
107
What do ribosomes and DNA in the stroma do?
Synthesise some proteins that make up the chloroplast
108
What are two other types of plastids?
Chromoplasts
| Leucoplasts
109
What colour are chromoplasts?
Red, orange and /or yellow pigments
110
What do chromoplasts do?
Give colour to plant organs such as flowers
111
What do leucoplasts do?
Storage deposits for starches and fats
112
What are peroxisomes?
Organelles that collect toxic peroxides (hydrogen peroxide for example)
113
Where do toxic peroxides come from?
Unavoidable by-products of cellular chemical reactions
114
How big are peroxisomes?
0.2 to 1.7 micrometers
115
What type of membrane do peroxisomes have?
Single membrane
116
What is inside a peroxisome?
Granular interior containing specialized enzymes
117
Where can peroxisomes be found?
Found (at one time or another) in (at least some cells of) all eukaryotic species
118
What similar to peroxisome structure can be found only in plant cells?
Glyoxysome
119
Where are glyoxysomes most prominent?
Young plants where stored lipids are converted to carbohydrates
120
What have vacuoles?
Many eukaryotic cells- plants and protists in particular
121
What do vacuoles contain?
Aqueous solutions containing dissolved substances
122
What are the 4 functions of plant vacuoles?
- Storage
- Structure
- Reproduction
- Digestion
123
How does storage in vacuoles contribute to the survival of plants?
Toxic and waste by products are stored in vacuoles which is poisonous/distasteful and deters animals
124
How does the vacuole contribute to plant structure?
90% of cell volume is taken up
| Vacuole causes water to enter the cell which swells, providing turgor (stiffness) to support plant
125
How do vacuoles help plants to reproduce?
Some pigments (blue and pink) called anthocyanins are contained in the vacuole and attract pollinating/dispersal animals
126
Where are food vacuoles found?
Some simple ancient groups of eukaryotes (single celled protists, sponges)
127
What are food vacuoles for?
No digestive system, cells engulf food particles by phagocytosis, generating food vacuole which fuses with a lysosome for digestion
128
Where are contractile vacuoles found?
Freshwater protists
129
What do contractile vacuoles do?
Get rid of excess water that rushes into the cell because of solute potential
130
How does the contractile vacuole expel water?
It expands as water enters, then abruptly contracts.
| Forces water through special pore structure
131
What is the cytoskeleton?
Long thin fibers
132
What are the roles of the cytoskeleton?
- Supports shape
- Movement
- Position organelles
- Tracks or support for motor proteins
- Anchors cell in place
133
What two methods show if a structure or process causes a function?
- Inhibition
| - Mutation
134
How does inhibition prove a structure or process causes a function?
Drug inhibits the structure or process- if the function does not occur then the structure/process is probably a causative factor
135
How does mutation prove a structure or process causes a function?
Look at cells that lack the structure or process and see if the function still occurs
136
What drug breaks apart the microfilaments of the cytoskeleton of an amoeboid cell?
Cytochalasin B
137
What happens when an amoeboid cell is treated with cytochalasin B?
It rounds up and does not move
138
What three components make up the cytoskeleton?
Microfilaments
Intermediate filaments
Microtubules
139
How do microfilaments exist?
Single, in bundles or in networks
140
What is the diameter of a microfilament?
7 nanometers
141
What are the two major roles of microfilaments?
Help entire cell or parts move
| Determine and stabilize cell shape
142
What are microfilaments made from?
Actin- a protein that exists in several forms
143
What is the structure of actin in microfilaments?
Extensively folded with plus and minus ends which interact to form long, double helix chains
144
What is the polymerisation of actin in microfilaments?
Reversible
145
What does actin produce in non-muscle cells?
Cytoplasmic streaming
Pinching that divides cells
Psuedopodia (false feet that enable movement)
146
What is cytoplasmic streaming?
Flowing movement of cytoplasm
147
How do actin filaments support cell shape?
Microfilaments form a meshwork inside plasma membrane which cross link and forms rigid structure
148
Where do microfilaments form a meshwork?
Microvilli that line human intestine
149
How many types of intermediate filaments are there?
At least 50- specific to cell type
150
How many molecular classes do intermediate filaments fall into?
6, based on amino acid structure
151
What are intermediate filaments composed of?
Fibrous proteins in keratin family
152
How are intermediate filaments arranged?
Tough, rope-like assemblages, 8-12 nm in diameter
153
What are the two structural functions of intermediate filaments?
Stabilize cell structure
| Resist tension
154
What do some intermediate filaments do?
Radiate from nucleus and maintain position of nucleus and organelles
155
Give an example of intermediate filaments.
Lamins of nuclear lamina
156
Give an example of intermediate filaments maintaining rigidity of body surface tissues.
Connecting spot welds, desmosomes, between adjacent cells
157
What are microtubules?
Long, hollow, unbranched cylinders
158
What is the diameter if microtubules?
25nm
159
What are the two roles of microtubules?
- Form rigid internal skeleton in some cells
| - Framework along which motor proteins can move structures
160
What are microtubules assembled from?
Tubulin (a protein)- made up of alpha and beta tubulin
161
What is tubulin?
A dimer- made of two monomers
162
What is the structure of a microtubule?
13 chains of tubulin dimers surround central cavity with a + and - end
163
Why are tubulin known as dynamic structures?
Tubulin dimers can be added or subtracted rapidly, mainly at the + end (lengthens and shortens)
164
Where do microtubules radiate from?
Microtubule organising center
165
What do microtubules do in plants?
Help control arrangement of cellulose fibers of the cell wall
166
What are motor proteins?
Specialized molecules that use energy to change their shape and move
167
What are microtubules essential in during cell division?
Distributing daughter chromosomes
168
What are eukaryotic cilia and flagella made from?
Specialized microtubules- idential internal structure, differ only in length and beating pattern
169
What are some characteristics of cilia?
Shorter than flagella
Present in great numbers
Beat stiffly in one direction, recovery flexibly in other direction
170
What are some characteristics of eukaryotic flagella?
Longer than cilia
Found singly or in pairs
Waves of ending propogates from one end to the other
171
What is the structure of eukaryotic cilia/flagella?
9 + 2 array
9 fused pairs of microtubules (doublets) to form outer cylinder
1 unfused pair up the middle
172
What is at the base of every cilia/flagella?
Basal body in the cytoplasm
173
What are centrioles?
Found in microtubule organising center- almost idential to basal bodies.
Not found in plants or protists
174
What are centrioles involved in?
Formation of mitotic spindle to which chromosomes attach
175
What is the movement of cilia/flagella the result of?
Sliding microtubule doublets past each other
176
What motor protein causes microtubules to slide past each other?
Dynein
177
How does dynein work?
It is attached to one microtubule doublet and then binds to its neighbor and changes shape
178
What motor protein carries vesicles from one part of a cell to another?
Kinesin
179
How does kinesin move proteins to other parts of a cell?
Binds to vesicle or organelle and then walks it along microtubule by changing shape
180
What molecule moves attached organelles towards the plus end of the microtubule?
kinesin
181
What molecule moves attached organelles towards the minus end of the microtubule?
Dynein
