Cells And Organelles Flashcards
1
Q
What are eukaryotic cells?
A
Contains clearly defined nucleus and membrane bound organelles. (Animal, plant, fungi and protists cells)
2
Q
What are prokaryotic cells?
A
Unicellular organisms that does NOT contain a membrane bound nucleus or organelles. (Bacteria and Aschaea)
3
Q
What is the size of Eukaryotic cells ?
A
10-100 micrometers
4
Q
What is the size of prokaryotic cells?
A
0.2-5 micrometers
5
Q
Where is DNA kept in eukaryotic cells?
A
DNA is kept within the nucleus
6
Q
What does the cytoskeleton do in eukaryotic cells?
A
-provides mechanical strength
-controls shape and regulates movement
7
Q
What do the internal membranes/ organelles do in eukaryotic cells?
A
Encloses spaces in cells often involved in digestion and secretion.
8
Q
What are the different types of cells within our body ?
A
-nerve cells
-Gut cells
-Skin cells
-Red blood cells
9
Q
Why cell renewal/division is relevant to plasma membrane?
A
- major rearrangement in membrane associated structures occurs as cells progress from interphase through prophase, prometaphase, metaphase, anaphase, telophase and late telophase
- The PM undergoes major shape change during mitosis so must be flexible
10
Q
What are the roles of plasma membrane?
A
-When immersed in water, these molecules aggregate to form bi-layers enclosing aqueous compartments
- Selective barrier to allow to concentrate nutrients, excrete waste products
-All cells have membrane transport proteins embedded within bi-layer
11
Q
What are the properties of PM?
A
-Allows small, uncharged molecules to pass through freely (polar or non-polar)
- does not allow macronutrients and ions to pass through freely,
- have specific trans-membrane proteins to regulate ion and molecule movements
-selectively allow some molecules to pass because its semi permeable
12
Q
What is lateral diffusion?
A
The proteins move laterally within the cell membrane – lateral diffusion
13
Q
What is the permeability of the PM?
A
- Semi-permeable
-Small, non polar molecular pass fast and easily - small polar molecules pass slowly
-large non polar molecules pass slowly
14
Q
What are the three major classes of membrane lipids?
A
-phospholipids
-cholesterol
-glycolipids
15
Q
What are the most abundant lipids in cell membranes?
A
Phospholipids- they are amphipathic
16
Q
What is the meaning of amphipathic?
A
A molecule which has both hydrophilic and hydrophobic parts
17
Q
What is the composition of the Phospholipid bilayer
A
18
Q
What is an amphipathic lipid?
A
19
Q
What are the different types of amphipathic lipid aggregates ?
A
20
Q
What is the difference in the nucleus in eukaryotic and prokaryotic cells?
A
The nucleus is membrane bound in eukaryotic cells and is absent in prokaryotic cells
21
Q
What are the major components of the plasma membrane
A
-lipids
-proteins
-carbohydrates
22
Q
What is flip-flop diffusion?
A
Lipids can move both laterally and rotate 360 degrees
23
Q
What are the three major kinds of membrane lipids in the PM?
A
-phospholipids
-glycolipids
-cholesterol
24
Q
Are lipids and proteins in the cell membrane fixed?
A
No, they are constantly moving
25
what is the most abundant lipid in the cell membrane?
Phospholipids which are amphipathic
26
What is the structure of a phospholipid?
-hydrophilic head and hydrophobic tails
- hydrocarbon tails
-unsaturated tail, saturated tail
-polar head
-glycerol backbone
27
What are the 4 major phospholipids?
-phosphatidylcholine and sphingomyelin (extra cellular)
-Phosphatidylethanolamine and phosphatidylserine (inner leaflet)
28
What is the minor phospholipid that makes up the PM?
Phosphatidylinositol which is a minor component in cytosolic leaflet but important for signaling
29
How much of the PM is made up of lipids ?
50%
Glycolipids- 2%
Cholesterol-5%
30
What is a amphipathic lipid?
-molecules that are mostly lipid-like in structure (hydrophobic) but at one end have a region that is polar (hydrophilic). This is usually referred to as the head group and the lipid portion is known as the tail.
31
What are the different types of amphipathic lipid aggregates?
-Micelles
-Bilayer
-Liposome
32
What enzyme catalyses transverse diffusion of lipids?
Flippase
33
What enzyme catalyses transverse diffusion of lipids?
Flippase
34
What is membrane fluidity influenced by?
-Temperature
-Phospholipid composition
35
What happens to membrane fluidity as temperature decreases ?
As temperature decreases the movement of lipids decreases so there is less fluidity
36
What is phospholipid composition influenced by ?
- length of hydrocarbon chains
-the number of double bonds- unsaturated hydrocarbon tails are more fluid as they are loosely packed
37
How does cholesterol influence membrane fluidity ?
-short, rigid cholesterol between unsaturated phospholipids
38
How does temperature affect cholesterol?
-At warm temperatures, cholesterol restrains movement of phospholipids. (Decreases fluidity
- At cool temperatures, it maintains fluidity by preventing tight packing
39
What features increase cell fluidity?
- short tails
-more double bonds
-less cholesterol
-less packed together
-high temperature
40
What features decrease cell fluidity?
-long tails
-few double bonds
-more cholesterol
-more packed together
-lower temperature
41
Why is the PM referred to as the fluid mosaic model?
PM is made up of different cells that are fluid.
Mosaic is art that is made of a variety elements.
42
where are glycolipids found in the PM
Extra cellular
43
What is the role of glycolipids?
Markers for cellular recognition
Provide energy
Attaching cells to each other to form tissues
Maintain stability
44
What are lipid rafts?
Microdomains with specific lipid components
45
what is the role of lipid rafts?
-Signal transduction
-membrane trafficking
-organization of the cytoskeleton
-pathogen entry
46
How much of the PM is made up of proteins?
50%
47
what are the different types of proteins?
-transporters and channels
-anchors
-receptors
-enzymes
48
Where are carbohydrates in the PM?
They are extra cellular and can be attached to lipids and proteins
49
What do carbohydrates in the PM form?
Glycoalyx which provides cushioning and protection for the PM and its also important in cell recognition
50
What are the different modes of transport?
-Diffusion
-facilitated diffusion
-active transport
51
What is the difference between passive transport and active transport?
Passive transport doesn’t require energy whereas active transport requires ATP
52
What are examples of different active transporters?
-uniporter- 1 molecule
-co-transporter - 2+ molecules
- antiporter- Molecules go in opposite directions
53
What are cell junctions?
Bridges between cells that allow communication
54
What are the different cell junctions?
-gap junction
-desmosome
-adherents junction
-tight junction
55
Tight junction functions
1. They limit the passage of molecules and ions through the space between cells. This pathway provides tighter control.
2. They block the movement of integral membrane proteins between the apical and basolateral surfaces of the cell.
3. Seal adjacent epithelial cells in a narrow band just beneath their apical surface. They consist of a network of claudins, occludins and other proteins
56
Adherens Junctions functions
They provide strong mechanical attachments between adjacent cells.
Examples:
1. They hold cardiac muscle cells tightly together as the heart expands and contracts.
2. They hold epithelial cells together.
3. They seem to be responsible for contact inhibition.
4. They are made up from Cadherins and Catenins
57
desmosomes functions
1.Localized patches that hold two cells tightly together. They are common in epithelia (e.g., the skin). Also called Anchoring junctions!
2. Desmosomes are attached to intermediate filaments of keratin in the cytoplasm.
3. The adhesion protein bridges the space between the cells.
4. Fasten cells together into strong sheets. (for example it attached muscle cells to each other in a muscle).
58
Hemidesmosomes function
Similar to desmosomes but attach epithelial cells to the basal lamina ("basement membrane") instead of to each other
59
Gap junctions function
Intercellular channels (1.5–2nm in diameter). Also called Communication junctions!!
They permit the free passage between the cells of ions and small molecules (up to a molecular weight of about 1000 daltons).
They are cylinders constructed from 6 copies of transmembrane proteins called connexins.
Because ions can flow through them, gap junctions permit changes in membrane potential to pass from cell to cell
60
What are organelles ?
Intracellular membrane-bound structures in eukaryotic cells, usually specialized for a particular function
61
Why do we have organelles ?
The compartmentalization provided by cytoplasmic organelles is what allows eukaryotic cells to function efficiently
62
What are the key functions of the plasma membrane ?
Separates contents of the cell from the environment
Regulates entrance/exit of molecules
Cell recognition of foreign cells and microorganisms
63
What does the cytoplasm contain ?
Water
ORGANELLES
Dissolved gasses
Ions
Enzymes
Proteins
Nucleotides
Amino acids
Sugars
Carbohydrates
Organic molecules
64
What is the function of the cytoplasm ?
-The compartments in the cytoplasm (organelles) allow metabolic reactions to occur and suspends organelles.
-Helps in the production and distribution of molecules by compartmentalization (Organelles again…).
-Materials can move around the cell…..
-The first step of energy production –(Glycolysis) takes place in the cytoplasm
65
What is cytosol ?
The semi fluid component of the cytoplasm
66
What is the cytoplasm made up of ?
1. Cytosol (the semi fluid component/liquid medium)
2. Organelles
3. Cytoplasmic inclusions which are particles that are temporary suspended in cytoplasm such as:
Secretory inclusions (acids, proteins, enzymes)
Nutritive inclusions (Glucose, lipids, Glycogen-glucose storage molecules)
Pigment granules (melanin)
67
What is the function of the cytoskeleton ?
-Provides support for cell shape (structural framework).
-Provides general organization of the cytoplasm.
—Facilitate substance and cell movement by providing a framework within the cytoplasm.
-Cytoplasmic streaming (cyclosis): movement of cytoplasm to circulate nutrients, organelles and other substances. Also helps in endocytosis, exocytosis and transport of substances into and out of the cell.
68
What is the cytoskeleton ?
3-D network of proteins fibres (filaments) connected to most organelles. The protein fibres within the cytoplasm act like a support structure.
69
What 3 filaments are the cytoskeleton made up of ?
-Microtubules
-Microfilaments
-Intermediate
70
What are Microfilaments ?
-Thin, solid rods (composed of twisted pairs of polymers of contractile protein G-actin that is removed in –ve and added in +ve end).
-8nm in diameter.
71
What are intermediate filaments ?
-They form keratins found in epithelial cells and neurofilaments in neurons.
-10 nm in diameter.
72
What are microtubules
-Hallow rods (polymers of tubulin dimers-they are heterodimers of a & b tubulin), functioning primarily to help support and shape the cell.
-They vary in length but their diameter is 25nm.
-Anchoring organelles and serving as structural components of the nuclear lamina.
73
What is the function of the nucleus ?
-Stores genetic information as DNA
-Contains genetic information for making proteins.
-Controls all cellular activities and protein synthesis
74
what is the structure of the nucleus ?
The nuclear envelope encloses the DNA and defines the nuclear compartment. This separates the contents from the cytoplasm. The information centre of the cell, where DNA is stored, replicated and transcribed into RNA
75
What is the structure of the nuclear envelope
The nuclear envelope is a double membrane that consists of phospholipids and protein pores (nuclear pores).
76
What is the function of the nuclear envelope ?
-Separation from the cytoplasm
-Transfer of molecules (mRNA, rRNA, nucleotides, proteins and enzymes) between nucleolus and cytoplasm via the nuclear pores.
77
What is the function of the nucleolus
A ribosome production factory where ribosomal RNAs are synthesized, processed and assembled with ribosomal proteins.
78
What is the structure of the nucleolus ?
-It is within the nucleus.
-2 or more darker spherical bodies present in non-dividing cells
-It contains the rRNA, rDNA and proteins
79
What is the structure of ribosomes ?
-They consist of protein and rRNA- that is produce in the nucleolus -(ribonucleoprotein)
-They are not membrane bound! They can be free, suspended in the cytoplasm or attached to ER.
80
What is the function of ribosomes ?
-The site of producing proteins
-Transcription - post-transcriptional modification -
translation
81
What is the Endomembrane system ?
The endomembrane system is a series of compartments that work together to package, label, and ship molecules.
82
What organelles does the endomembrane system contain ?
-Endoplasmic reticulum
-Golgi apparatus
83
What is the endoplasmic reticulum ?
A network of membrane-enclosed tubules and sacs that extends from the nuclear membrane throughout the cytoplasm.
84
What is the role of the RER?
which is covered by ribosomes on its outer
surface, functions in protein processing (carbohydrates are contributed to protein systems/glycoproteins more adjustment & processing in Golgi)
85
What is the role of the SER ?
not associated with ribosomes and is involved
in lipid, rather than protein, metabolism. Role in cellular metabolism(SER consists of many enzymes), storage & metabolism of calcium and detoxification.
86
What is the function of ER?
Proteins and lipid membranes are assembled in the ER.
Major site at which membrane lipids are synthesized in eukaryotic cells
The proteins secreted by cells are also directed to the ER during translation.
They are packaged for vesicular release from the cell. (The hormone insulin is an examples of such a protein.)
87
What is the structure of the Golgi ?
Consists of 6 or more stacked, flattened membranous sacs (saccules/ cisternae One side faces the nucleus and the ER (cis) and the other side faces the cell membrane (trans).
At the edges of the Golgi there are some small membranous sac called vesicles.
88
What is the function of the Golgi ?
-Modifies/Process
-Packages
-Stores
-Distributes proteins produces by ribosomes on ER into vesicles to be exported or transported to other sites in the cells
-Hydrolytic enzymes into lysosomes
89
What are vesicles ?
Small membrane enclosed sacs that are pinched off portions of membranes moving from the site of one membrane to another.
90
What is the structure of mitochondria ?
-Surrounded by a double membrane
-Inner and outer mitochondrial membranes separated by an intermembrane space.
-The inner membrane forms numerous folds which extend into the matrix of the organelle (cristae). They represent the major working compartments of mitochondria.
-They retain their own small genome. Contain their own DNA, which encodes tRNAs, rRNAs, and some mitochondrial proteins.
-Primarily use proteins encoded by the nuclear genome and imported from the cytosol.
-Divide independently of the cell cycle by simple fission
91
What is the function of mitochondria ?
-Undergoes process of aerobic cellular respiration.
-synthesis of ATP
92
What are lysosomes
-Membrane-bound organelles containing a variety of enzymes (hydrolases) that can digest proteins, nucleic acids, lipids, and complex sugars.
-The lumen of a lysosome is more acidic than the cytoplasm. All acid hydrolases are most active at the acidic pH (~5).
-This pumping requires expenditure of energy in the form of ATP.
93
What is the structure of the cell vacuole ?
-A large membrane-enclosed sac. Vary widely in size, number and function.
-Intracellular structures surrounded by a membrane which cells use for storage. (nutrients, water and waste products)
-Cells with vacuoles have relatively less cytoplasm, and the presence of a large central vacuole can push organelles towards the periphery of the cell.
94
What is the function of cell vacuoles ?
-Storage of macromolecules such as a food vacuole formed by phagocytosis.
-Storage of water and/or waste products.
95
What is the main function of the ER ?
It is the site of modification of proteins following their translation from RNA
96
Which eukaryotic cellular organelles are believed to have evolved from symbiotic bacteria ?
Mitochondrial and chloroplasts
97
What is the PM
A flexible phospholipid bilayer with protein molecules embedded and glycoproteins and glycolipids attached to it.
98
What is endoplasm and ectoplasm in terms of cytoplasm ?
Endoplasm- the central area containing the organelles
Ectoplasm- gel-like peripheral portion of the cytoplasm
99
Where are Microfilaments present ?
present in all eukaryotic cells but prevalent in muscle cells (active in muscle contraction )
100
What is the role of Microfilaments in the cytoskeleton ?
participate in organelle movement-acts like a track for movement of actin
101
Where are intermediate filaments found ?
Abundant in many cells
102
What is the role of intermediate filaments in the cytoskeleton ?
provide support for Microfilaments and microtubules by holding them in place
103
Where are microtubules found ?
Found in all eukaryotic cells
104
What is the role of microtubules in the cytoskeleton ?
-Involved in cell-cell and cell-matrix junctions
-anchoring organelles and serving structural components of the nuclear lamina
-Role in intracellular transport, formation of Celia/flagella and mitotic spindle
105
What is movement along microtubules and Microfilaments based on?
Motor proteins
106
What are the 2 main motor proteins
Kinesins and dyneins
107
How do motor proteins produce movement
Derive energy from ATP hydrolysis to produce force and movement
108
Which direction does kinesins move organelles
Outward transport towards PM
109
Which direction does dyneins move organelles
Backwards transport to nucleus
110
Which direction does dyneins move organelles
Backwards transport to nucleus
111
What are nucleoporins
Nucleoporins make up the nuclear envelope and allow substances to move in and out of the nucleus
112
How do these organelles work together in order to carry out certain functions ?
Both proteins and lipids travel along the secretory pathway in transport vesicles, which bud from the membrane of one organelle and then fuse with the membrane of another.
