Eukaryotic cell structure and function

Question 1

What is life

Answer 1

The state or quality that distinguishes living beings or organisms from inorganic matter

Metabolism
Response
Sensitivity
Growth
Reproduction
Excretion
Nutrition

Question 2

What are cells

Answer 2

fundamental units of life

Question 3

What defines a cell?

Answer 3

• Discrete, easily recognisable packages (cell membranes)
• made up of phospholipids which prevent the entry of hydrophilic compounts

Question 4

What are the chemical properties of cells?

Answer 4

• all cells are similar inside
• they are composed of the same sort of molecules
• information flows from DNA via RNA to proteins
• proteins influence cell behaviour

Question 5

What is the composition of cells?

Answer 5

• 70% water
• 30% varying chemicals and proportions of structural and functional molecules

Question 6

Give physical properties of prokaryotic cells and examples

Answer 6

• eg spherical cells, rod shaped cells, spiral cells

• typically spherical, rod like or corkscrew shaped
• protective cell wall surrounding plasma membrane
• no organelles, circular DNA
• typically single celled, aerobic or anaerobic

Question 7

What are the physical properties of eukaryotic cells?

Answer 7

• Larger and more complex than prokaryotes
• can be unicellular or part of multicellular organisms
• linear DNA molecules
• chromosomes in nucleus, chromosome number and ploidy widely variable
• membrane bound organelles

Question 8

What are the functions of the plasma membrane

Answer 8

• Regulate transport (eg nutrients, waste)
• Maintain ‘proper’ chemical conditions
• Provide a site for chemical reactions unlikely to occur in aqueous environment
• Detect signals in the extracellular environment
• Interact with other cells or the extracellular matrix

Question 9

Role of Nucleus

Answer 9

membrane bound structure, separates DNA from cytosol, transcription from translation (see genetics)

Question 10

role of endoplasmic reticulum

Answer 10

RER: protein synthesis

SER: lipid and steroid synthesis

Ca2+ ion storage & detox

Question 11

role of ribosomes

Answer 11

50% protein and 50% rRNA

used for protein synthesis, often associated w RER

Question 12

role of golgi complex/apparatus

Answer 12

series of flattened discs called cisternae, modifies and sorts most ER products

Question 13

role of mitochondria

Answer 13

Site of ATP production via aerobic metabolism, important role in apoptosis, self replicating (fission)

Question 14

What are the properties of mitochondrial DNA?

Answer 14

• Mitochondria contains multiple mtDNA molecules
• genes in mtDNA exhibit cytoplasmic inheritance and encode rRNAs, tRNAs, and some mitochondrial proteins
• the size and coding capacity of mtDNA varies considerably in different organisms
• products of mitochondrial genes are not exported
• mutations in mtDNA cause several genetic diseases in humans

Question 15

role of lysosomes

Answer 15

•degrade certain cell components, material internalised from the environment
• appear
as electron dense bodies on EM
• single membrane
• pH of lumen 3.5-5
• contains acid hydrolases
• if lysosomal enzyme is missing eg hydrolytic enzymes (generic defect): accumulation of material leads to lysosomal storage disease

Question 16

role and features of peroxisomes

Answer 16

role:
• responsible for degrading:
- fatty acids eg oxidation of them
- toxic compounds eg alcohol oxidation

features:
- single membrane
- contain oxidases (eg urate oxidase and catalase)
- can be diverse in size and enzyme composition eg special plant peroxisomes

Question 17

composition of cytoskeleton

Answer 17

3 major filamentous compounds:
• microtubules ~25nm (tubulin)
• actin filaments ~6nm (actin)
• intermediate filaments ~10nm (different subunit proteins)

Question 18

role of cytoskeleton

Answer 18

• Essential in movement of cellular components and the cell itself
-maintains cell shape
-vesicular transport
-cell division

• Number of accessory proteins associated with with the filamentous components

Question 19

function of actin

Answer 19

• maintains cell shape by resisting tension (pull)
• moves cells via muscle contraction or cell crawling
• divide animal cells into two
• move organelles and cytoplasm in plants, fungi, and animals
• cell shape and whole cell locomotion
• cells which need to move rich in actin

Question 20

function of intermediate filaments

Answer 20

• maintain cell shape by resisting tension
• anchor nucleus and some other organelles
• rope like fibrous proteins (defined by size)
• abundant cytoplasmic and nuclear proteins
• provide structural reinforcement and stress resistance

Question 21

function of microtubules

Answer 21

• maintain cell shape by resisting compression
• move cells via flagella or cilia
• move chromosomes during cell division
• assist formation of cell plate during plant cell division
• move organelles
• provide tracks for intracellular transport
• dynamic (end grows rapidly)

Question 22

What are motor proteins

Answer 22

(not enough to have cytoskeleton)
• need motors to move vesicles
• three superfamilies identified with multiple members
• presence of conserved amino acids sequence, forms the ATP-binding and force-producing motor domain

Question 23

What does the motor protein Myosin do

Answer 23

acts on actin- cell surface contractions- morphological changes- vesicle motility- muscle cell contractions

Question 24

what does the motor protein Dynein and kinesin do?

Answer 24

Interact with microtubles to move vesicles and organelles, movement of flagella and cilia- essential in mitosis and meiosis in function of the spindle

Question 25

What are the physical properties of myosin?

Answer 25

• expressed in virtually all eukaryotic cells
-couple hydrolysis of ATP to conformational changes

• head (motor domain)
- ATP and actin binding site
- exhibits actin activated ATPase activity

• Neck region
- an extended a helix

• Tail region
- effector domain
- determines specific function

Question 26

What are the properties of Dynein and Kinesin?

Answer 26

• cytoplasmic motors:
- Dynein: large mass, higher complexity, activity can be dynamically regulated
- Kinesin: simpler structure, either active or inactive

• both move in one direction only
- dynein: moves towards - end of microtubule
- kinesin: move towards + end of microtubule
- force and movement generated by ATP hydrolysis

•involved in many processes (eg cell division, intracellular transport)

Question 27

What mutations in the cytoskeletal components can lead to disease?

Answer 27

• actin mutations: congenital myopathy
• intermediate filament mutation: >30 human disease
• microtubule mutations/disfunction : neurodegeneration

Question 28

How do we use cytoskeleton as a target?

Answer 28

•Pharmaceutical agents can be used to target cytoskeletal components
- eg polymerisation of filaments
- colchicine, causes microtubule depolymerisation, may contribute to its role in treating gout

•targeting cancer
- vinca alkaloids and paclitaxel disrupting cell cycle progression by inhibiting mitotic microtubules

• can also target assessory proteins, and ECM
- integrins are target for antiplatelet drugs