L2: Cells & Organelles

Question 2

cells vary dramatically in size

Answer 2

bacteria (~1 micrometer)
ostrich egg (~.1 m = 100,000 micrometers)

typical human cell is about 10-50 micrometers in diameter

Question 3

cells vary dramatically in shape

Answer 3

Question 4

size scales relevant to cell biology
1 meter = —- mm/micrometers/nm

Answer 4

Question 5

resolving power (resolution) definition

Answer 5

the ability to distinguish two close objects

maximum RP depends on the wavelength of the illumination

Question 6

visible light has a wavelength of

Answer 6

400-700nm and can resolve objects about 200 nm apart

Question 7

size scales relevant to cell biology

Answer 7

.2 mm = minimum resolvable

200nm = minimum resolvable by light icroscope

.2nm = minimum resolvable by electron microscope

Question 8

cells have thousands of different proteins. how to find just one?

Answer 8

1. indirect immunofluorescence
2. GFP

Question 9

indirect immunofluorescence

Answer 9

1. specificity - uses an antibody to your protein of interest, the “antigen”
2. sensitivity - fluorescence - a molecule is fluorescent if it absorbs light of one wavelength and
   then emits light of a different (longer) wavelength – very sensitive

can only be done by killing the cells!

Question 10

how does IF use antibodies to tag antigens?

Answer 10

First steps: ‘Fix’ cell (chemical cross-linking) and make cell permeable to antibodies using a detergent to dissolve the plasma membrane

Question 11

green fluorescent protein (GFP)

Answer 11

1. Sensitivity - uses GFP fluorescence
2. Specificity - GFP protein “fusion”

Question 12

transmission electron microscopes (TEM)

Answer 12

Question 13

pros and cons to electron microscopy

Answer 13

EM pro: Much better resolution than light microscopy (more detail)

EM con: Much more effort to get 3D view of the cell (“tomography”)

More difficult to label specific proteins

Cannot be used on live cells (imaging is done in a vacuum)

Highest resolution is tricky because of damage to sample caused by electrons

Question 14

nucleus

Answer 14

Contains the ‘genome’ (most of the cellular DNA)

Darker regions are the “nucleolus” – this is where ribosomes are assembled.

Question 15

plasma membrane

Answer 15

separates the cell from the environment

Question 16

endoplasmic reticulum

Answer 16

Primary site for synthesis of lipids, membrane proteins, and secreted proteins

Sections of ER with ribosomes bound are called “rough ER”

Question 18

golgi complex/apparatus

Answer 18

Performs modifications on secretory proteins

Central sorting station for vesicle trafficking

Question 19

mitochondria

Answer 19

have 2 membranes + their own genome + ribosomes

more closely related to bacterial genomes and ribosomes than to the Eukaryotic nuclear genome and ribosomes in the cytosol

major site of ATP production

consumes and produces many metabolites

not bean-shaped, form dynamic tubular networks

Question 20

chloroplasts

Answer 20

responsible for photosynthesis

have their own genome + ribosomes

more closely related to bacterial genomes and ribosomes than to the eukaryotic nuclear genome and ribosomes in the cytosol

Question 21

cytoplasm vs. cytosol

Answer 21

cytoplasm = all the stuff in between the plasma membrane and the nucleus

cytosol = the soluble portion of the cytoplasm

Question 22

why do eukaryotes contain internal membranes

Answer 22

Allows compartmentalization of function
-cells perform many competing reactions that need to be separated (ie. protein synthesis and protein degradation

Allows more membrane surface per cell volume
-many reactions are carried out on membranes
-larger cells have smaller ratio of cell surface to volume