Unit 2 Chapter 7: Cells

Question 1

What are chromosomes (in prokaryotes)

Answer 1

• the most prominent structure in bacterial cells

- usually have 1 circular one (large DNA molec with some proteins)

Question 2

How does DNA fit into small cells

Answer 2

DNA double helix coils on itself with the help of enzymes to form the highly compacted “super coil structure”

Question 3

Where are bacterial chromosomes found

Answer 3

in the nucleoid (usually in center/20% of cells volume)

NOTE: nucleoid is enclosed by a membrane

Question 4

What are plasmids (prokaryotes)

Answer 4

small, circular, usually super-coiled DNA molecs found in bacteria that contain genes but are physically independent of the main circular chromosome
-can be considered auxiliary genetic elements as the genes inside them are not usually required

Question 5

What are ribosomes

Answer 5

• structures that manufacture proteins

- in bacteria they contain RNA and proteins

Question 6

Describe the photosynthetic membranes in prokaryotes

Answer 6

• contain the enzymes and pigment molecs required for photosynthesis to occur and develop as infoldings of the plasma membrane
• sometimes vesicles pinch off as membrane folds in
• sometimes flattened stacks of photosyn membrane form the infolds in the plasma membrane
• large surface area allows for more reactions to occur

Question 7

What are 4 key tasks of bacterial organelles

Answer 7

1. storing calcium ions or other key molecs
2. holding magnetite crystals which act as a compess and sense a magnetic field and swim in a directed way
3. organizing enzymes in charge of making carbon compounds from CO2
4. hiding enzymes that generate chemical energy from ammonium ions

Question 8

What is the cytoskeleton (prokaryotes)

Answer 8

long thin fibres made of long polymers of globular proteins that serve as structural support
-responsible for shape, cell division, transport of plasmids and organization of cell interior

Question 9

What are flagella (prokaryotes)

Answer 9

• enable species to swim by rotating like a propeller
• tail-like structure
• few in # and located on cell surface
• made of flagellin
• no membrane

Question 10

Describe the structure and function of the cell wall in prokaryotes

Answer 10

• structure: tough, fibrous layer that surrounds the plasma membrane
• resists pressure that is exerted due to inward water flow from osmosis. protects cell and gives it shape and rigidity

Question 11

Why is compartmentalization beneficial?

Answer 11

• incompatible chem reactions can be separated

- chemical reactions become more efficient

Question 12

What is the nucleus

Answer 12

• brain of cell
• contains chromosomes and is the info storage and processing centre
• enclosed by a DOUBLE membrane

Question 13

What is the nuclear envelope

Answer 13

double membrane that encloses nucleus and is studded with openings/inside surface is linked to fibrous proteins that form a sheet called the nuclear lamina
-continuous with endomembrane system

Question 14

What does the nuclear lamina do

Answer 14

stiffens structure and maintains shape

Question 15

Do chromosomes float freely in the nucleus

Answer 15

no, each has a distinct spot and is attached nuclear lamina in at least one spot

Question 16

What is the nucleolus

Answer 16

distinct region in nucleus where RNA found in ribosomes are made and small ribosomal subunits are assembled

Question 17

What is the ER

Answer 17

extensive series of membrane bound sacs extending from nuclear envelope into cytoplasm

Question 18

What is the difference between smooth and rough ER

Answer 18

rough=has attached ribosomes that make proteins to be inserted into the plasma membrane, secreted to the outside of the cell or shipped to an organelle; rough ER products are packaged into vesicles and transported

smooth=no ribosomes, contains enzymes that catalyze lipid reactions, manufactures phospholipids, reservoir for Ca ions (signalling)

Question 19

What is the golgi apparatus

Answer 19

flattened membranous sacs (cisterna) which are stacked

• organizes, packages and ships proteins (processing and sorting)
• cis-faces ER
• trans-faces membrane

Question 20

What does the cis side of the golgi body do

Answer 20

receives products from rough ER

Question 21

What dies the trans side of the golgi body do

Answer 21

ships the products away towards cell surface

Question 22

What are ribosomes (eukaryotes)

Answer 22

made of 4 rRNAs and 80 proteins, make proteins, NOT classified as an organelle because not surrounded by a membrane

Question 23

What are peroxisomes

Answer 23

globular organelles: contain enzymes, centres for oxidation reactions, have a single membrane and originate as buds from the ER

Question 24

What are lysosomes

Answer 24

digestive centres

Question 25

What is autophagy

Answer 25

- a damaged organelle is brought in and delivered to a lysosome - its digested - small molecs from the digestion are released into the cytosol

Question 26

What is phagocytosis

Answer 26

cell eating - plasma membrane detects a cell or particle and engulfs it creating a phagosome - delivered to lysosome and digested - small molecs from the digestion are released into the cytosol

Question 27

What is pinocytosis

Answer 27

cell drinking - fluid brought into cell via tiny vesicles that form infoldings of plasma membrane - fluid used elsewhere in cell

Question 28

What is receptor mediated endocytosis

Answer 28

think claw machine - molec binds to membrane proteins that act like receports - membrane folds off and pinches in to form an early endosome - endosome undergoes processing ie;. activation of proton pumps that lower pH - early endosome matures into a late one and recieves digestive enxymes from golgi body - late endosome turns into lysosome

Question 29

What are vacuoles

Answer 29

large storage depot usually for water or ions

Question 30

What is the mitochondria

Answer 30

powerhouse of cell - has 2 membranes - contains DNA (chromosomes) which allows them to make some of their own proteins - have own ribosomes - plastids - have cristae which increase SA to fill membrane with proteins and make ATP

Question 31

What are chlroroplasts

Answer 31

- has DNA - in plants, mature form of plastids, convert solar energy into chemical energy for photosynthesis - has a double membrane - thylakoids stacked into grana which are all in stroma - larger than mitochondria

Question 32

What is lignin

Answer 32

forms a branching cave like network that is impossible for enzymes to attack in the secondary cell wall that some plants produce

Question 33

Why are cells small

Answer 33

surface area to volume ratio, most reactions require diffusion and diffusing molecules don't travel long distances due to their random walk

Question 34

What is included in the endomembrane system

Answer 34

ER, golgi body, vesicles, nuclear and cell mebranes

Question 35

What happens in the nucleus

Answer 35

DNA is replicated, DNA is transcribed in to mRNA and rRNA, mRNA is translated rRNA is not

Question 36

Why is rRNA not translated

Answer 36

it directly folds into a 3D structure

Question 37

What does the animal pancreatic cell do

Answer 37

exports digestive enzymes

Question 38

What does the animal testis cell do

Answer 38

exports lipid soluble signals

Question 39

What is the evidence that mitochondria and chloroplasts are descendants of bacteria (endosymbiont theory)

Answer 39

1. double membrane 2. own genome 3. own ribosomes more similar to eubacteria 4. genes more similar to eubacteria genes

Question 40

What was the Pulse-Chase experiment

Answer 40

used to research the secretory path way: pulse=expose exp. cells to a high concentration of a labelled molec for a short time chase=larger amounts of unlabelled version of the same molec for a longer time results support the secretory path way that proteins move from ER to golgi to secretetion

Question 41

What is the signal hypothesis

Answer 41

1. ribosome synthesizes ER signal sequence 2. signal sequence binds to a signal recognition particl:SRP 3. ribosome+SRP+ signal sequence attaches to SRP receptor in ER membrane 4. once receptor and SRP connect, SRP is released 5. signal sequence removed and protein synthesis is completed

Question 42

What are the possible "fates" for proteins

Answer 42

stay in endomembrane system, sent to lysosomes, plasma membrane for exocytosis or outside of the cell

Question 43

What are actin filaments and what is their function

Answer 43

-microfilaments -made of actin -polar, has a + and - end -treadmilling=the addition or subtracting of actin molecs to each end (tend to grow at + end) -structure resembles two long strands coiled around eachother Function: structural support, cell shape by resisting tension, movement (myosin head binds to actin for movement), divide cells, move organelles

Question 44

What are intermediate filaments and what is their function

Answer 44

- non-polar - fibres wound into thicker cables - purely for structure: resist tension (pull), anchor nucleus and organelles - made of keratin, vimentin or lamin

Question 45

What are microtubules

Answer 45

- hollow tubes of alpha and beta tubulin - largest cytoskeletal components - polar, usually grow at their + end - originate from MTOC, which contains centrosome that contain 2 bundles of microtubules called called centrioles - provide stability + movement via flagella/cilia, resist compression, move chromosomes during division, move organelles, intracellular transport, formation of cell plate in plant division

Question 46

What happens if microtubules are prevented from forming

Answer 46

ER no longer assembles in its normal network-like config

Question 47

What is kinesin

Answer 47

like actin it is a motor protein, which acts like a delivery truck to move transport vesicles down the microtubule tracks -it "walks" along the tracks when it's head region binds to ATP

Question 48

What are flagella (eukaryotes)

Answer 48

- made of microtubules - move cell by whipping back and forth - plasma membrane - evolved independently from bacteria flagella - closely related to cilia

Question 49

What is dynein

Answer 49

-a motor protein -changes shape when phosphate from ATP binds to it -change in shape moves molecule along microtubule -when dynein reattaches it has succeeded in walking a step along the microtubule doublet (allows microtubule doubles to slide past eachother) -walks in opposite direction of kinesin -bends cilia and flagella

Question 50

What allows microtubules/axonemes to bend

Answer 50

if dynein arms on one side of axoneme walk and cause some doublets to slide while those on the other side are at rest -in cilia/flagella this causes swimming

Question 51

How are molecular postal codes read

Answer 51

they bind to receptor proteins

Question 52

Where does translation always begin

Answer 52

in the cytosol