Biology Chapter 6 (A Tour of the Cell)

Question 1

definition of Prokaryotic cells and its components

Answer 1

-defined by absence of membrane bound nucleus

components:
-nucleoid (houses circular DNA)
-ribosome (synthesizes proteins)
-plasma membrane (encloses cytoplasm)
-flagella (locomotion)
-cell wall (rigid structure outside membrane)
-cystosol (jelly-like fluid)

Question 2

3 key differences between Prokaryotic and Eukaryotic

Answer 2

1) Eukaryotic is bigger
2) Prokarayotic chromosomes have loosely defined nucleoid; Eukaryotic chromosomes are enclosed in nucleus
3) cytoplasm of Eukarytoic cells is compartmentalized into distinct organelles rather than everything found in cytoplasm

Question 3

Advantages of compartmentalization

Answer 3

1) chemical reactions are organized and can be partitioned
2) reactions are more efficient because reactants can be isolated and maintained at higher concentrations
3) enzymes can be grouped together in close proximity for efficiency

Question 4

Nucleolus (Eukaryotic-Nucleus)

Answer 4

Where Ribosomal RNA is synthesized and where the subunits of ribosomes are assembled

Question 5

Nuclear Envelope (Eukaryotic-Nucleus)

Answer 5

double membrane (double phospholipid bilayer)

Question 6

Pore Complexes (Eukaryotic-Nucleus)

Answer 6

regulate entry and exit of proteins and RNA

Question 7

Ribosomes

Answer 7

-no membranes (so they are not considered organelles by classical definition)
-either bound or free
-two subunits associated non-covalently for easier association and disassociation
-consists of nucleic acids (ribosomal RNA) and proteins

Question 8

Parts of the endomembrane system

Answer 8

-Outer nuclear envelope
-Endoplasmic Reticulum
-Golgi Apparatus
-Lysosomes
-Vacuoles
-Plasma Membrane

Components are either continuous (connected by membranes) or interact via movement of membrane bound vesicles

Question 9

Endoplasmic Reticulum and components (Endo-membrane system)

Answer 9

Smooth ER:
-system of membrane bound sacs and tubules
-[lacks ribosomes]
-contains enzymes involves in lipid based reactions. Site of phospholipid production for cell membranes and lipid detoxification/breakdown
-can store intracellular calcium. Keeping surrounding region low in calcium ions. Difference in concentration can be used for signaling

Rough ER:
-system of membrane bound sacs and tubules
-[ribosomes] generate proteins that function in ER, endomembrane system or that get secreted to cell exterior

Lumen:
-gaps in ER where protein folding and modification happens
-For ER synthesized proteins

modifications to proteins can happen in ER (ex. glycosylation)

Ratio of Smooth ER/Rough ER depends on cell and its function (ex. testes produce hormones which are made of lipids so they have a lot of smooth ER).

Question 10

Golgi Apparatus (Endo-membrane system)

Answer 10

site of protein processing, folding and shipping

movement from cis(side close to ER) to trans (furthest from ER)

this process could involve membrane bound transport vesicles that assist with movement of proteins through the golgi

Question 11

Lysosome (Endo-membrane system)

Answer 11

membranous sac of enzymes that perform hydrolysis (collectively called acidic hydrolases that function most optimally in acidic environments)

-proton pumps are required to maintain acidic conditions

-can also be referred to as a recycling component because smaller subunits from lysosomal degradation are exported out by transport proteins in the membrane of the lysosome to build other molecules

-Endoplasmic reticulum synthesizes the enzymes and membrane

-produced proteins processed by the golgi are shipped to the lysosome so this is why they are considered part of endomembrane system

Question 12

phagocytosis (Endomembrane system)

Answer 12

a process where cells engulf other cells or food particles forming a vesicle (food vacuole/phagosome) that then binds to a lysosome resulting in degradation of components

Question 13

autophagy (Endomembrane system)

Answer 13

a process used to recycle large structures and organelles.

-portions of the cytoplasm are enclosed within internal membrane to form a phagosome(vesicle) which merges with a lysosome to degrade the components

-the broken down contents can be recycled and ultimately get released to the cytosol

Question 14

Vacuoles

Answer 14

can be found in plant cells

vacuoles replace lysosomes in plant cells. Some have hydrolases but many are used for storage (pigments, proteins for seeds, toxins depending on organism)

Question 15

Mitochondria

Answer 15

significant ATP generator

Has two membranes (inner and outer):
-outer defines the structure
-inner has folding of sac like structures called cristae

cellular respiration: series of events that takes place along membrane and within matrix (contents within folding) of mitochondria

christae increase surface area

the mitochondria does contain linear chromosomes (mitochondrial DNA) that are independent of nuclear chromosomes.

only a fraction of genes in mitochondrial DNA is responsible for the function of the mitochondira

Some of the DNA encodes for RNA for mitochondrial ribosomes which produce some of the proteins found in mito, but most proteins in mito are produced by free ribosomes in cystosol

Question 16

chloroplasts

Answer 16

Contains the green pigment chlorophyll and enzymes and molecules for photosynthesis

Has two membranes inner and outer. Inner has no christae

Has a third membrane found within the chloroplast called the thylakoids that are arranged in a stack called granum (plural grana)

Question 17

peroxisomes

Answer 17

Site of reduction and oxidation reactions (transfer of electrons between atoms and molecules

An example of a reaction that takes place within the peroxisome is ethanol oxidation which produces hydrogen peroxide.

Hydrogen peroxide is reactive and harmful if it escaped the membrane bound organelle (compartmentalization partitions the reaction)

So there is an enzyme in the peroxisome whose role is to detoxify hydrogen peroxide into water and oxygen

Question 18

Cytoskeleton network and its components

Answer 18

the cytoskeleton organizes structures and activities and anchors organelles

cytoskeleton is dynamic
-moves and changes to accommodate alterations to the cell shape
-can be involved with the movement of the cell itself

consists of 3 types of molecular structures
1) microtubules
2)microfilaments
3)intermediate filaments

Question 19

microtubules (cytoskeleton)

Answer 19

largest cytoskeleton components with respect to diameter

has polypeptide subunits (alpha and beta tubulin) which associate non-covalently to polymerize. The subunits form the tubulin dimer

has polarity (a negative and a positive end)
-this is relevant because the rate of polymerization is not equal on either end

microtubules provide structural framework for organelles and separate genetic material during cell division. Also supports movement of cargo by allowing motor proteins to use the tubulin as a track

Question 20

centrosome (a pair of centrioles)
centrioles (9 triplets of microtubules arranged in a ring)

Answer 20

in animal cells, microtubules originate from the centrosome

the ends are where polarity applies for a microtubule:
- positive end is area that grows faster
- the origin is the negative end
- positive end points away
- rate of polymerization/depolymerization is higher on the positive end

Question 21

kinesin

Answer 21

motor protein that binds to the tubulin subunits to move towards the positive end of the microtubule

uses atp hydrolysis (atp to atp +pi) to take each step

made of two polypeptide subunits and has three regions on the protein (head, stalk and the tail)

head region binds to the tubulin and the tail region transports the vesicle

stalk connects head and tail

Question 22

dynein

Answer 22

motor protein that moves towards the negative end of the microtubule (towards the origin)

Question 23

microfilaments/actin filaments (cytoskeleton)

Answer 23

smallest component of cytoskeleton

composed of actin subunits associated non-covalently in a twisted chain

has polarity (positive end grows faster than negative end)

found under the plasma membrane and helps define the shape of the cell. Microfilaments are also involved in movement (amoeba move with actin protrusions and myosin can ratchet onto actin filaments and create muscle contractions)

Question 24

myosin

Answer 24

motor protein that binds to actin for muscle contractions

-ATP hydrolysis involved (changes orientation of myosin)

-Change in state allows myosin to ratchet onto the actin filaments and create contractions

-Also needs calcium ion from endoplasmic reticulum

Question 25

cytoplasmic streaming in plant cells

Answer 25

directional flow of cytosol and organelles along periphery of cell wall

movement occurs along actin filaments powered by myosin

Question 26

intermediate filaments (cytoskeleton)

Answer 26

bigger than microfilaments

role is exclusively structural in nature

no polarity/sidedness

found inside nuclear envelope (inner side) and defines the shape of the nucleus and stabilizes the envelope

An example of intermediate filaments are keratins coiled together. This is for mechanical strength and is one of the last components to degrade in decomposing body.

Question 27

Extracellular Matrix and components

Answer 27

the matrix found outside of cells that cells interact with

different tissue types will have different compositions of extracellular material

components:
-collagen (structural protein that imparts strength and flexibility)
-proteoglycan complex (protein-polysaccharide complex that provides the matrix that structural proteins are embedded in)
-fibronectin (adhesive glycoproteins that bind to proteoglycans and collagen molecules. Allows cells to attach to extracellular matrix. Composed of large polypeptides crosslinked by disulfide bridges)
-integrins (cell surface receptors that bind to ECM components. Composed of alpha and beta subunits associated non-covalently)
-glycoproteins()
-glycolipids()

Question 28

cell walls of plants (extracellular material)

Answer 28

confer rigidity, barrier to substance movement and protects cell from physical damage

the components of the extracellular matrix is different compared to animal cells because plant cell walls contain cellulose microfibrils

cell walls secreted and synthesized in different stages

primary cell wall (composed of cellulose microfibrils and defines shape of the plant)

secondary cell wall (some plants don’t have this but it is possible for secretion of additional layer between plasma membrane and primary cell wall after maturation)

middle lamela (strucutre holds adjacent cells together)

Question 29

tight junctions (animal cell junctions)

Answer 29

cell-cell attachment due to proteins in the plasma membrane of each adjacent animal cell

forms a tight seal that prevents things from passing through (good for stomach and intestines to prevent contents from leaking)

level of restriction of movement at tight junctions depends on the region of the body (different regions can have different tightness. Ex. bladder tighter than intestines bc intestines might want some level of absorption of nutrients and bladder deals with waste)

tight junctions can also change by stretching (ex. food moving through digestive track)

Question 30

desmosome (animal cell junctions)

Answer 30

proteins found in membrane that forms bridges between anchoring proteins in adjacent cells that provide strong adhesion sites between cells

allows cells to work as a unit and resist mechanical stress

desmosomes are abundant anywhere where mechanical stress is present (heart, uterus, skin, etc.)

loss of desmosomes can lead to heart failure or skin defects

intermediate filaments reinforce desmosomes by attaching to anchoring proteins

Question 31

gap junctions (animal cell junctions)

Answer 31

mechanism of cell communication

creates channels within membranes of adjacent cells which allow for movement of ions and small molecules

allows nearby cells to respond rapidly through fluctuations in concentration of ions and molecules (ex. heart has gap junctions to coordinate muscle contractions)

Question 32

plasmodesmata (plant cell junction)

Answer 32

plant cell specific occuring at regions where there are holes in the cell wall

provides opportunity for plasma membrane of adjacent cells to come into contact with each other

allows for sharing cytoplasm which is similar to animal gap junctions but not identical

unlike gap junctions, plasmodesmota is lined w/ plasma membrane and has a central tubule connecting the endoplasmic reticulum of the two cells

Question 33

bound ribosome products

Question 34

free ribosome product