The structure of Eukaryotic cells (lectures 3 and 4)

Question 1

Describe the key features of a eukaryotic cell.

Answer 1

• membrane-bound organelles

- have linear DNA molecules packaged as chromosomes enclosed in a nucleus

Question 2

What are the functions of the plasma membrane?

Answer 2

• regulation of transport
• nutrients into the cell, waste materials out
• maintains balance of chemical conditions i.e. homeostasis
• provides a site for chemical reactions not likely to occur in an aqueous environment
• interacts with other cells or the extracellular matrix

Question 3

What are the key features of the nucleus?

Answer 3

• contains genetic material
• electron microscopy reveals 2 membranes
• contents are in contact with cytoplasm via nuclear pores which pass through both membranes
• nucleolus: rich in protein and RNA which is involved in synthesis of ribosomal RNA and ribosomes

Question 4

What are the 2 membranes of the nucleus and their functions?

Answer 4

• inner membrane is in contact with the nuclear contents

- outer membrane appears to be continuous with endoplasmic reticulum

Question 5

functions of the rough endoplasmic reticulum?

Answer 5

-ribosomes attached to the surface

• plays a role in synthesising membrane-bound and secreted proteins
• extensive in cells synthesising these proteins

Question 6

functions of the smooth endoplasmic reticulum?

Answer 6

• carries no ribosomes

- plays a role in producing lipids eg membrne lipids and steroid hormones

Question 7

what are the key features of the endoplasmic reticulum?

Answer 7

responsible for

• lipid synthesis
• most membrane protein synthesis
• Ca2+ ion storage detoxification

Question 8

key structure and functions of ribosomes?

Answer 8

• multisubunit structures comprised of roughly 50% protein and 50% ribosomal RNA
• rRNA are key to the structure and function of ribosomes
• involved in the synthesis of proteins

Question 9

structure and function of mitochondria?

Answer 9

typically 0.5-10 micrometres in size

• contains DNA and ribosomes which are smaller than normal eukaryotic type
• self replicating: binary fission

sites of ATP production via aerobic metabolism
-play important role in apoptosis

Question 10

describe the key features of mitochondrial DNA

Answer 10

• mitochondria contain multiple mtDNA molecules
• genes in mtDNA exhibit cytoplasmic inheritance and encode rRNAs, tRNAs and some mitochondrial proteins
• mutations in mtDNA cause several genetic diseases in humans eg leigh syndrome, leber hereditary optic neuropathy

Question 11

explain the key structures and functions of the golgi apparatus

Answer 11

• stack of flattened membranous sacs which vary in number
• ensures that vesicles budding off outer face can fuse with plasma membrane
• packages lysosomal proteins and proteins to be secreted from cell

Question 12

what are the key features of the golgi complex

Answer 12

• series of flattened compartments and vesicles

- composed of 3 regions: cis (entry), medial and trans (exit)

Question 13

what is the function of lysosomes?

Answer 13

-single membrane-bound organelles containing hydrolytic enzymes

• hydrolytic enzymes degrade materials taken up by endocytosis and cell debris
• degrade damaged newly synthesised proteins

Question 14

what are peroxisomes

Answer 14

-single membrane-bound organelles

• contain catalase and urate oxidase
• breaks down very long chain fatty acids via beta oxidation

-oxidation of toxins inc alcohol

Question 15

3 key features of the cytosol of the cytoplasm?

Answer 15

• cytoskeleton
• polyribosomes
• metabolic enzymes

Question 16

function of the cytoskeleton?

Answer 16

involved in:

• cell movement
• cell division
• cell shape
• intracellular trafficking of organelles
• coordinated movement of tissues

Question 17

what are the 3 major components of the cytoskeleton

Answer 17

• microfilaments
• microtubules
• intermediate filaments

Question 18

functions of microfilaments?

Answer 18

F-actin filaments are double helices of polymerised G-actin subunits

• fibres expand and contract by further polymerisation and depolymerisation
• ATP dependent

microfilaments interact with other filaments and motors to create movement: contraction can cause shape change

Question 19

what do actin and myosin do?

Answer 19

• actin microfilaments work with myosin in muscle fibres
• myosin filaments walk along the tethered actin, hence pulling the filaments towards the centre to cause muscle contraction

Question 20

how do microtubules grow

Answer 20

-grow by polymerisation from specific microtubule organising centres

Question 21

role of microtubules?

Answer 21

fundamental role in partitioning of chromatids in cell division

Question 22

role of vacuoles?

Answer 22

• store water, ions, nutrients and degrade macromolecules
• inflow of water by osmosis causes vacuole expansion and maintenance of turgor pressure
• expansion of vacuoles involved in cell elongation

Question 23

role of chloroplasts?

Answer 23

-contain chlorophyll and other pigments that absorb light and generate NADPH and ATP during photosynthesis which is used to produce organic molecules

Question 24

structure of chloroplasts?

Answer 24

• double membrane bound
• contain their own DNA
• thylakoid membranes, fused into stacks called grana

-capture light to produce ATP during photosynthesis

Question 25

role of plasmodesmata?

Answer 25

directly connect the cytosol of adjacent cells in higher plants