Lecture 6, 7, 8: Cell Structure

Question 1

limitations to cell size based on SA:V

Answer 1

cell size is determined by limits:
-lower limit: need to have enough space to have DNA and all the macromolecules needed to function/survive
- upper limit: due to the exchange of materials through the plasma membrane

Question 2

prokaryotes vs. eukaryotes

Answer 2

Prokaryotes:
- DNA is centralised in the nucleotide
- Cell wall on the outside of their plasma membrane (made up of peptidoglycan)
- Glycocalyx: protective coating made up of glycoproteins and glycolipids
- Throughout cytoplasm are ribosomes that make proteins via translation
- Lack membrane-bound organelles
- Very tiny! 1-5 mu-meter

Eukaryotes:
- DNA in nucleus, bounded by membrane called nuclear envelope
- Some have cell walls (i.e. plants and fungi; plants: cellulose, fungi: chitin)
- Have a cytoskeleton for structure and support
- Throughout cytoplasm are ribosomes
- Have membrane-bound organelles
- Very large! 10-100 mu-meter

Question 3

endomembrane theory:

Answer 3

explains where eukaryotes came from
1. Came from heterotrophic prokaryotic cell
2. Plasma membrane of a prokaryotic lineage began invading into cytoplasm 2 billion years ago
3. These membranes eventually separated from the plasma membrane, surrounded the DNA to form a nucleus, and became the endomembrane system of the eukaryotic cell

Question 4

organelles of the endomembrane system

Answer 4

Nuclear envelope
Endoplasmic reticulum
Golgi apparatus
Lysosomes
Vesicles and vacuoles
Plasma membrane

Question 5

what are the functions of the EM system

Answer 5

• Protein synthesis
• Protein transport
• Metabolism
• Movement of lipids
• Detoxifying the cell

Question 6

ENDOPLASMIC RECTICULUM (the factory):

Answer 6

• Has an extensive network of flattened membrane sacks called cisternae
  (endoplasmic: within the cytoplasm, reticulum: little net)
• ER lumen is the space between ER membranes (space is continuous with the nuclear lamina)

Question 7

rough ER vs. smooth ER

Answer 7

ROUGH ER:
- Studded with ribosomes
- Continuous with the nuclear envelope
- Production of glycoproteins
- Separates and transports proteins out by transport vesicles
- Production of phospholipids and other proteins

SMOOTH ER:
- Lacks ribosomes
- Production of lipids
- Metabolises carbs
- Detoxifies the cell
- Storage of calcium ions

Question 8

GOLGI APPARATUS (the sorting facility):

Answer 8

• Series of flattened sacs (cisternae)
  -> “cis” side faces rough ER and is younger (receiving end)
  -> “trans” side points out towards rest of cell and is older (shipping end)
• Vesicles bring material from the rough ER to the cis face, fusing with the Golgi membrane
• Materials are modified as they pass through
• Vesicles pinch off of the trans face and head to their final destination within or outside the cell

Question 9

LYSOSOME (the digestor and recycler):

Answer 9

• Membranous sac of hydrolytic enzymes (pH 5)
• If lysosome ruptures (lyses), contents aren’t digested because the cytosol pH is too high for the enzymes (pH 7)

Question 10

VACUOLE (the transporter):

Answer 10

• Large vesicles made from the rough ER and Golgi apparatus
• Food and digestive vacuoles
• Contractile vacuoles (pump out excess water)
• Plant vacuoles (storage for small molecules, some hydrolysis of molecules, large central vacuole contains inorganic ions and swells up due to osmosis)

Question 11

MITOCHONDRIA: energy converter

Answer 11

• In most eukaryotic cells (except red blood cells)
• Site of cellular respiration
• Consists of two membranes: intermembrane space in between the two
• Inner membrane folded to make cristae which encloses the mitochondrial matrix
• Range in size
• # per cell varies depending on the function
• DO NOT make energy, just convert it

Question 12

CHLOROPLASTS: energy converter

Answer 12

• Only in plants/algae
• Absorbs energy from photons
• Energy = converted to ATP and NADPH (ex. Photosynthesis)
• Consists of two membranes: intermembrane space in between
• Inner membrane folded to make thylakoids which are stacked to form grana
• Range in size
• Contains chlorophyll (green pigment)
• DO NOT make energy, just convert it

Question 13

heterotrophs vs. autotrophs

Answer 13

hetero: organisms that obtain energy from consuming material
auto: creates their own energy

Question 14

anaerobes vs. aerobes

Answer 14

anaerobes: can survive in oxygen, can’t use it to extract energy for aerobic respiration
Aerobes: survives in oxygen, and can use it to extract energy for aerobic respiration

Question 15

endosymbiotic theory:

Answer 15

describes how mitochondria arose
1. Eukaryotic cell engulfed an aerobic heterotrophic prokaryotic cell that could use oxygen
2. Prokaryote was retained and became the mitochondria

Question 16

what are the three cytoskeletal elements

Answer 16

microtubules, microfilaments, intermediate fibres

Question 17

microtubules

Answer 17

structure: hollow tubes
protein subunits: tubulin
function: maintenance of cell shape, cell motility, chromosome movement, organelle movement

Question 18

flagella vs. cilia

Answer 18

flagella:
one per cell
longer than cilia
undulating motion

cilia:
many per cell
shorter than flagella
wave back and forth

Question 19

microfilaments

Answer 19

structure: two intertwined strands of actin
protein: actin
function: maintenance of cell shape, changes in cell shape, muscle contraction, cytoplasmic streaming in plants, cell motility, division of animal cells

Question 20

intermediate filaments

Answer 20

structure: fibrous proteins coiled into tables
protein: several kinds (ex. keratin)
function: maintenance of cell shape, anchorage of nucleus and certain other organelles, formation of nuclear lamina

Question 21

bacteria vs. eukaryote flagellum

Answer 21

The flagella in eukaryotes have dynein and microtubules that move with a bending mechanism. Bacteria and archaea do not have dynein or microtubules in their flagella, and they move using a rotary mechanism.

Question 22

three types of flagella

Answer 22

bacterial, archaeal, and eukaryotic

Question 23

what is flagellum

Answer 23

a slender threadlike structure, especially a microscopic appendage that enables many protozoa, bacteria, spermatozoa, etc. to swim

Question 24

what are bacterial pili?

Answer 24

Pili are short, hair-like structures on the cell surface of prokaryotic cells. They can have a role in movement, but are more often involved in adherence to surfaces, which facilitates infection, and is a key virulence characteristic

Question 25

cell walls:

Answer 25

extracellular structures in plant seas
maintains cell shape, prevents uptake of excess water, thicker than the plasma membrane, composed of cellulose
have a primary cell wall, with a middle lamella between the secondary cell wall
have plasmodesmata pores to allow substances to travel through the cell wall

Question 26

tight junctions:

Answer 26

plasma membranes of adjacent cells are held together by specialized proteins
Creates a seal, why we don’t lose water from our skin cells!

Question 27

anchoring junctions:

Answer 27

binding proteins
- Desmosomes from sheets of strongly connected cells
- Keratin anchors the desmosomes into the cytoplasm through the cytoskeleton

Question 28

gap junctions:

Answer 28

• Connects the cytosols of adjacent cells - kind of like pipes
• Allows for fast passage of ions and signaling molecules between cells to coordinate activity

Question 29

plasmodesmata:

Answer 29

plant-specific gap junctions
- Channels that connect adjacent cell walls and cytosol
- Water and small solutes can pass freely via these channels
- Can adjust their diameter to allow large molecules to pass through

Question 30

extracellular matrix (ECM)

Answer 30

the stuff outside the cell

Question 31

extracellular matrix vs. intracellular cytoskeleton

Answer 31

The intracellular cytoskeleton provides vital 3D support to the cytoplasm, transports organelles and is a means of locomotion. The extracellular matrix consists of macromolecules that provide strength, support and connection between cells of the tissue