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Eukaryotic Cell Structure Flashcards

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1
Q

What is the cell theory?

A
  1. All living organisms are composed of one or more cells
  2. The cell is the most basic unit of structure in all organisms
  3. All cells arise only from preexisting cells
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2
Q

What is the difference between the nucleus of a prokaryote and a eukaryote?

A

Prokaryote: no nuclear membrane or nucleoli
Eukaryote: true nucleus, consisting of nuclear membrane and nucleoli

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3
Q

What is the difference between the organelles of a prokaryote and a eukaryote?

A

Prokaryote: no membranous organelles
Eukaryotes: have membranous organelles (lysosomes, Golgi, endoplasmic reticulum, mitochondria, chloroplasts)

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4
Q

What is the difference between the ribosomes of a prokaryote and a eukaryote?

A

Prokaryote: smaller size, 70S
Eukaryote: larger size 80S, smaller size 70S in organelles

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5
Q

What is the difference between the chromosome (DNA) of a prokaryote and a eukaryote?

A

Prokaryote: singular, circular chromosome, lacks histones
Eukaryote: multiple linear chromosomes with histones arrangement

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6
Q

What are the functions that are characteristics of the fundamental unit of life?

A

MERRING

Movement
Excretion
Respiration
Reproduction
Irritable
Nutrition
Growth

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7
Q

Why are cells kept small?

A

Size of cell increases, surface area to volume ratio decreases, number of chemical exchanges that could be performed with the extracellular environment would be inadequate to maintain the cell as most of its cytoplasm is relatively far from the outer membrane

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8
Q

What are the non-membranous organelles?

A

Cytoskeleton
Centrioles
Centrosomes
Cilia
Flagella
Ribosomes

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9
Q

What are the membrous organelles?

A

Chloroplast
Mitochondria
Endoplasmic reticulum
Golgi. Apparatus
Lysosomes
Peroxisomes

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10
Q

What does the cytosol contain?

A
  1. Various essential ions and soluble organic molecules (sugars, amino acids)
  2. Soluble proteins (enzymes)
  3. Cytoskeleton (a network of fine strands of globular and fibrous proteins, provides infrastructure and support to the cell)
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11
Q

Advantages to membrous organelles?

A
  1. Maintenance of characteristic differences between contents of each organelle and cytosol
    - provides different local environments for incompatible processes to occur simultaneously
  2. Increase membrane surface area
    - internal membranes allow for embedding of enzymes and proteins
    - greater membrane surface area, larger number of enzyme of complexes that can be embedded, increases efficiency of reactions by providing optimal enzyme concentration
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12
Q

What is the nucleus?

A

Largest organelle
Spherical/oval in shape
5-20 micrometers

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13
Q

Purpose of nucleus?

A

Encloses genetic material anad protectsDNA from metabolically active cytoplasm
Double membrane is perforated with pores to enable exchange of substances between the nucleus and cytoplasm

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14
Q

What does the nucleus consist of?

A

Nuclear envelope
Nucleoplasm
Nucleolus

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15
Q

What is the nuclear envelope? Purpose?

A

Double membrane (continuous with each other, each a lipid bilayer): separates contents of nucleus from cytoplasm
Outer membrane: continuous with membrane of ER
Space between inner and outer membranes: perinuclear space

Perforated by nuclear pore (add up of a large protein complex)
Purpose: allow macromolecules (mRNA, rRNA) to exit the nucleus and allow proteins (enzymes) to. Enter and exit the nucleus

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16
Q

What is the nucleoplasm?

A

Aqueous matrix within the nucleus containing proteins, metabolites, ions, RNA, chromatin

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17
Q

What is chromatin composed of?

A

Coils of DNA wound around basic protein (histones)

Euchromatin: loosely coiled chromatin (light-coloured patches in electron micrograph of nucleus)
Heeterochromatin: tightly coiled chromatin (dark-coloured patches in electron micrograph of nucleus)

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18
Q

What is the nucleolus?

A

Dense mass in nucleus when viewed under electron microscope

Made of DNA carrying rRNA genes, RNA and protein
Functions to synthesised a specific type of RNA (ribosomal RNA) that forms a component of ribosomes

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19
Q

What are the membranous organelles involved in the endo-membrane system?

A

Rough and smooth endoplasmic reticulum
Golgi apparatus
Lysosomes
Vacuoles

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20
Q

What is the endoplasmic reticulum?

A

Extensive network of HOLLOW, MEMBRANOUS TUBULES, SACS OR SHEETS called CISTERNAE (singular: cisterna)

Cisternal space: lumen, continuous with perinuclear space

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21
Q

How to distinguish ER from Golgi apparatus?

A

ER: flatter,more compact packing that is sheet-like

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22
Q

How does the structure of ER support its function?

A

1.extensive network of cisternae, increases membrane surface area for synthesis
RER: embedded with ribosomes for synthesis of polypeptides
SER: embedded with enzymes for synthesis of steroid and phospholipid

  1. Hollow cisternae, accommodate newly synthesised substances, allow for packing of contents into vesicles for transport GA (budding of vesicles)
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23
Q

Structure of RER?

A
  1. Sheet-like appearance
  2. appear rough: presence of ribosomes that stud the cytosolic face
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24
Q

Function of RER?

A

RER bound ribosomes: site of protein synthesis where a polypeptide chain is synthesised at the bound ribosome
Polypeptide chain enters ER lumen (site of protein folding) and a protein channel in the RER membrane (polypeptide chain folds into its native conformation)
Proteins are destined for export/targeted to various cellular organelles
- contrast to proteins synthesised by free ribosomes in cytosol which remain in cytosol)

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25
What cells have abundant RER?
Cells active in protein excretion Some proteins synthesised in RER can directly enter membrane of ER to form ER membrane protein Proteins that leave the RER: enclosed in transport vesicles
26
What is the SER?
Network of tubules which lack ribosomes
27
Function of SER?
1. Synthesis of lipids, oils, phospholipids, steroids like sex hormones) 2. Metabolism of carbohydrates 3. Detoxification of drugs and poisons 4. Storage of calcium ions for use in muscle contraction and cell signalling
28
What cells have abundant SER?
Cells active in hormone secretion - due to synthesis of lipids (oils, phospholipids, sex hormones)
29
What is the Golgi apparatus?
Site of modification and packaging of ER products A stack of flattened, membrane-bound sacs called cisternae Distinct polarity! Cis face (forming face): new cisternae constantly being formed by receiving transport vesicles from ER, membranes of transport vesicles from ER fuses with cis face membrane and deposits their contents into Golgi cisternal space Trans face (maturing face): membranes bud off to form secretory vesicles, contain materials to be transported to the extracellular matrix Membranes: also bud off from Golgi trans face to form lysosomes
30
Purpose of golgi vesicles?
Transfer materials between the Golgi sacs Transport substances to other organelles in the cell
31
Function of Golgi Apparatus?
GLYCOSYLATION (addition of sugar groups) TRIMMING (removal of excess monomers) ER products: progressively modified as they move through th stacks of the Golgi complex from cis face to trans face, processed and packaged content are passed on to other components of the cell by vesicles that bud off the GA
32
What cells have abundant GA? Why?
Cells active in any form of secretion! Abundant flattened cisternae: increased surface area for vesicle reception and budding Multiple cisternae: different modification processes can occur simultaneously
33
What is a lysosome?
A membranous organelle Appears homogenously electron-dense under EM
34
What do lysosomes contain?
Hydrolytic enzymes (proteases nucleases, lipases, acid phosphotases) Can digest most biological macromolecules
35
Where are enzymes contents in lysosomes synthesised?
Synthesised on RER, transported to GA for further processing
36
Why are lysosomes membranous organelles?
Acidic (pH 5) nature of lysosome contents and hydrolytic activity Contents must be prevented from spilling into cytoplasm under normal cell conditions Segregation of contents within membrane provides optimal pH for hydrolytic reactions, protects cellular contents from hydrolysis
37
What are the 3 major functions of lysosomes?
1. Digestion of materials taken into cells - food engulfed by endocytosis, form food vacuoles, food vacuoles fuse with lysosomes to form endosomes - enzyme digests endosome contents which end up in cytosol to be used as food for the cell Phagocytosis vacuole: defence mechanism against bacteria 2. Autophagy of worn-out organelles - unwanted structures enclosed within membrane of unknown origin to form a vesicle, vesicle fuses with lysosome to form autophagic vacuole 3. Autolysis - self destruct in a controlled manner (apoptosis) - requires mass release of lysosomal contents in whole cell
38
Are vacuoles present in animal cells, plant cells or both?
BOTH!
39
Structure and function of vacuoles in animal cells?
Small, mobile organelles House and transport substances (food vacuoles, phagocytic vacuoles)
40
Structures of vacuole in plant cells?
Large central vacuole surrounded by a single membrane (tonoplast) Solution within tonoplast: cell sap (differs in composition from cytoplasm)
41
Function of vacuole in plant cells?
1. Storage of inorganic compounds (proteins) ad inorganic ions (potassium cation, chloride anion) 2. Disposal site for toxic metabolic by-products 3. Contains pigments (red, blue pigments that colour the petals) 4. Plant protection, accumulates compounds that are toxic or unpalatable to consumers 5. Cell growth and elongation, water accumulates in vacuole, can increase in size with minimal investment in cytoplasm synthesis and without sacrificing surface area to volume ratio (cytoplasmic contents are pushed to the periphery of the cell)
42
Similarities between mitochondria and chloroplasts?
Double membrane Have their own DNA and protein synthesis machinery Involved in energy transduction
43
What type of cells have abundant mitochondria?
Cells with high levels of metabolic activity
44
What is the mitochondria a site for?
Sites of aerobic respiration (catabolic process that generates ATP by extracting energy from sugars, fats and other metabolic fuels in the presence of oxygen)
45
How does the structure of the mitochondria relate to its function?
STRUCTURE: enclosed in double membranes, each with a unique collection of proteins and enzymes Outer membrane: smooth Inner membrane: highly convoluted, with infoldings known as cristae (singular: crista) FUNCTION: increase surface area to volume ratio for attachment of various enzyme systems and involved in cellular respiration
46
What is the inter-membrane/perinuclear space?
Narrow, fluid filled space between the 2 mitochondrial membranes
47
What is the mitochondrial matrix?
Compartment enclosed by inner membrane Contains enzymes, circular DNA, RNA, ribosomes (for synthesis of proteins) Site of Krebs cycle
48
Why is the compartmentalisation of the mitochondrial matrix necessary?
To set up a proton gradient across the inner mitochondrial membrane Proton gradient due to inner mitochondrial membrane being impermeable to protons
49
What are chloroplasts sites of?
Photosynthesis! Convert solar energy to chemical energy by absorbing sunlight, use it to drive the synthesis of organic compounds from carbon dioxide and water Synthesis of ATP and NADPH, used in Calvin Cycle
50
Shape/structure of chloroplast?
Lens-shaped 5-10 micro meters in length The only organelles other than nucleus visible under light microscope Surrounded by double membrane (chloroplast envelope)
51
What is the stroma? What does the stroma contain?
Semi-fluid compartment enclosed by inner membrane Contains circular DNA (to enable synthesis of chloroplast proteins) Sugars synthesised by chloroplasts stored as starch grains in stroma Contains enzymes required for light-independent reactions (Calvin Cycle) of photosynthesis
52
What is the thylakoid?
Third set of membranes within the stroma Area enclosed: thylakoid lumen
53
What is the thylakoid disc?
A flattened sac of the thylakoid and thylakoid lumen together Stacks of thylakoid discs form a granum
54
What connects the stacks of grana?
Intergranal lamellae (sheet-like thylakoids)
55
Purpose of thylakoids?
Site for light-dependent reactions of photosynthesis Increased surface area for attachment of chlorophyll and other photosynthetic pigments
56
Why is the compartmentlisation of thylakoid lumen necessary?
To set up a proton gradient across thylakoid membranes, due to thylakoid membranes being impermeable to protons
57
What are ribosomes sites of?
Protein synthesis
58
What is each ribosome made of?
2 subunits Large ribosomal subunit Small ribsomal subunit Both made up of proteins and ribosomal RNA
59
Where are ribosomes found?
1. Attached to RER (80S) 2. Free in cytosol (80S) 3. Mitochondrial matrix (70S) 4. Chloroplast stroma (70S)
60
What are ribosomes attached to RER called? Purpose?
Bound ribosomes Synthesis proteins for 1. Export 2. Insertion into membrane 3. Targetted to various membrane-bound organelles (lysosomes)
61
What are ribosomes floating in the cytosol called? Purpose?
Free ribosomes Synthesis proteins that remain in the cell and function within the cytosol/nucleus
62
Are centrioles found in plant cells, animal cells or both?
ONLY animal cells Location: near nucleus, at the centrosome that contains specific listed proteins required for microtubule assembly
63
Structure and purpose of centrioles?
Found in pairs at right angles to each other Each member of the pair consisting of nine triplets of microtubules arranged in a ring Before cell division: 1. Each centriole replicates itself and move to opposite poles of the cell 2. Centrosome act as MTOC for formation of spindle fibres that play a role in nuclear division
64
What is a cell wall?
Rigid and inflexible Made of structural polysaccharide cellulose Supports and defines the shape of plant tissues
65
Function of cell wall?
1. Protects cells from mechanical injury and invasion 2. High tensile strength, enables cell to withstand the hydrostatic pressure exerted by uptake of water by the cell, enables plant cells to prevent excessive uptake of water
66
Is the plant cell wall freely permeable?
YES! Except for very large molecules
67
What is the region between the cell walls of adjacent cells separated by?
Middle Lamella Rich in polysaccharides like pectin, helps the cell adhere together
68
How to calculate magnification in microscopy?
Drawing/image size DIVIDED BY actual size of specimen
69
Define resolution
The shortest distance that is found between 2 points that can be distinguished by the observer
70
What is the purpose of cell fractionation? What are the 2 main steps?
Purpose: studies of isolated organelles Steps: 1. HOMOGENISATON: Disruption of cells and release of the individual cellular components 2. DIFFERENTIAL CENTRIFUGATION: purification/separation of cell components
71
Purpose of homogenisation?
To break tissues into smaller fragments and release organelles
72
Methodology of homogenisation
Mechanically rupture the cell membrane - mortar, pestle and abrasive material (sand, silica etc) - homogeniser/blender - pressure cell - ultrasound - osmotic lysis using a hyperosmotic homogenisation medium to rupture protoplasm’s Chemically dissolve membrane phospholipids:various detergents
73
What are some precautions when carrying out homogenisation? (For integrity of organelles)
1. Isotonic medium containing sucrose, mannitol or sorbitol 2.buffer solution to maintain suitable pH 3. Temperature of 4°C to inhibit protease activity
74
Purpose of differential centrifugation?
Separate organelles using centrifugation
75
Methodology of centrifugation
Homogenate is subjected to progressively increasing speeds and duration of centrifugation to separate particles in descending order of size and density Sendimntation coefficient: affected by shape, size and density Faster rotation, greater gravitational force generated, smaller particles sedimented After each speed, supernatant (liquid above pellet) can be drawn off and recentrifuged at a higher speed for a longer duration Series of pellets containing cell organelles of smaller and smaller size can be obtained
76
Principle of centrifugation
Most intracellular organelles are discreet particles that have unique sizes and densities
77
What is autoradiography?
Use of X-ray film to visualise molecules or fragments of molecules that have been radioactivey labelled
78
Purpose of autoradiography?
- identify sites of synthesis and cellular distribution of metabolic products by tagging specimen molecules with radioisotopes - used with LM or EM to trace secretion products and their intermediates from their synthesis sites
79
Methodology of autoradiography?
Cells/tissue sections incubated with radioactive substances After substance has been taken up, cell/tissue is mounted on a glass slide which is dipped into photographic emulsion (decay of radioactive isotopes results in a dark spot on photographic emulsion, allowing for identification of location of radioactive substance)
80
Structure of a typical bacteria cell?
Small and unicellular Peptidoglycan cell wall Circular DNA 70S ribosomes Lack of membrane bound organelles

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