Chapter 3 - The Cellular Level of Organization

Question 1

What are the 3 Major Parts of a Cell?

Answer 1

1- Plasma Membrane (or Cell Membrane)
2- Cytoplasm (Cytosol, Organelles)
3- Nucleus (Chromosomes, Genes)

Question 2

What is the Plasma Membrane?

Answer 2

Plasma Membrane is a flexible sturdy barrier that surrounds the cell and contains Cytosol

Made of a phospholipid bilayer
Has Membrane proteins:
Peripheral proteins
Integral (or Transmembrane) proteins
Glycoproteins
Glycolipids

Question 3

What are the 2 Types of Membrane Proteins?

Answer 3

Integral (or Transmembrane) Protein
Peripheral Protein

Question 4

What are the Functions of Membrane Proteins?

Answer 4

Ion Channel (Integral) - Lets ions in or out
Carrier (Integral) - Transports specific substances in or out
Receptor (Integral) - Recognize specific Ligands and alters cell’s function
Enzyme (Integral and Peripheral) - Catalyzes reaction
Linker (Integral and Peripheral) - Provide structure and stability
Cell Identity Marker (Glycoprotein) - Distinguish self-cells form foreign cells

Question 5

What is Membrane Fluidity?

Answer 5

Membranes are fluid structures
Most membrane lipids and proteins move easily in the bilayer

Cholesterol serves to stabilize the membrane and reduce fluidity

Question 6

What is Membrane Permeability?

Answer 6

Plasma Membranes are selectively permeable

Lipid bilayer always permeable to small, nonpolar, uncharged molecules

Transmembrane proteins act as channels or transporters increasing permeability

Macromolecules are only able to pass by vesicular transport

Question 7

What is the Electrochemical Gradient across the Plasma Membrane?

Answer 7

Electrochemical Gradient is made of Concentration Gradient and Electrical Gradient

Concentration Gradient:
Difference in concentration of a chemical between both sides of plasma membrane

Electrical Gradient:
Difference in concentration of ions between both sides of plasma membrane

Question 8

What are the 2 types of Transport across the Plasma Membrane?

Answer 8

1- Passive Transport:
Simple Diffusion
Facilitated Diffusion
Osmosis

2- Active Transport:
Primary Active Transport
Secondary Active Transport
Vesicular Transport

Question 9

What is Simple Diffusion?

Answer 9

Movement of solutes from areas of high concentration to areas of low concentration

Influenced by;

1- Steepness of concentration gradient
Bigger - faster

2- Temperature
Higher - faster

3- Mass of diffusion substance
Lower - faster

4- Surface area
Bigger - faster

5- Diffusion distance
Shorter - faster

Question 10

What is Facilitated Diffusion?

Answer 10

Transmembrane proteins help solutes that are too polar or too highly charged move through plasma membrane

2 Types:

Channel-Mediated facilitated Diffusion
Specific to unique ion
Usually gated

Carrier-Mediated facilitated Diffusion
Changes shape to open and let specific solute pass

Question 11

What is Osmosis? And what is Tonicity?

Answer 11

Osmosis: the net movement of a solvent (water) through a selectively permeable membrane from an area of high concentration to an area of low concentration

Tonicity: how the solution influences the shape of body cells

ex:
RBC in solution
Isotonic - equal movement of water between RBC/solution, RBC normal
Hypotonic - water enters RBC until bursts, RBC undergoes Hemolysis
Hypertonic - water exits RBC, RBC undergoes Crenation (shrivel)

Question 12

What is Primary Active Transport?

Answer 12

Energy derived from ATP changes shape of transporter protein which pumps a substance across plasma membrane against its concentration gradient (from area of low concentration to area of high concentration)

ex:
Na/K Pump
ATP binds to Na/K pump and promotes binding of Na+ to pump
Binding of Na+ to pump hydrolyze ATP into ADP and P binds to pump
It causes a conformational change of pump
This lets 3 Na+ ions exit into the ECF
At same time, 2 K+ ions bind to pump and release P from pump
This causes another conformational change to the pump
And lets 2 K+ ions into the ICF
Pump back to original shape ready to bind to another ATP

Question 13

What is Secondary Active Transport?

Answer 13

Coupled Active Transport of 2 substances across the membrane using energy from H+ or Na+ concentration gradient to drive substances against their concentration gradient (from low to high)
Maintained by primary active transport pumps

Antiporter: Moves Na+ (or H+) and another substance in opposite directions
Symporter: Moves Na+ (or H+) and another substance in same directions

ex:
Antiporter - Na+ goes into ICF and Ca2+ (or H+) goes out to ECF
Symporter - Na+ goes into ICF and Glucose (or Amino Acid) goes into ICF

Question 14

What is Receptor-Mediated Endocytosis?

Answer 14

Ligand-receptor complexes trigger infolding of a clathrin-coated pit that forms a vesicle containing ligands

Vesicle uncoats, receptors go back to membrane
Vesicle fuses with endosome
Receptors go back to membrane in a transport vesicle
Another transport vesicle takes the ligands and fuses with lysosome
Degradation in lysosome

Question 15

What is Phagocytosis?

Answer 15

Cell Eating
Movement of a solid particle (bacteria, virus, aged/dead cells) into a cell after pseudopods engulf it to form a Phagosome

Phagosome fuses with Lysosome, digest contents by lysosomal enzymes, residual body remaining

Question 16

What is Bulk Phase Endocytosis (Pinocytosis)?

Answer 16

Cell Drinking
Movement of ECF (solutes in ECF) into a cell by infolding of plasma membrane to form a vesicle

Vesicle fuses with Lysosome, digestion by lysosomal enzymes, digested solutes go in ICF

Question 17

What is Exocytosis?

Answer 17

Movement of substances out of a cell in secretory vesicles that fuse with plasma membrane and release their contents in ECF

(Neurotransmitters, Hormones, Digestive Enzymes)

Question 18

What is Transcytosis?

Answer 18

Movement of a substance through a cell as a result of Endocytosis on one side and Exocytosis on the opposite side

(Substances like antibodies across endothelial cells)
(Common route for substances to pass between blood plasma and interstitial fluid)

Question 19

What is the Plasma Membrane? And what is its Function?

Answer 19

Fluid mosaic lipid bilayer (phospholipids, cholesterol, and glycolipids) studded with proteins
Surrounds Cytoplasm

Function:
Protect cellular contents
Makes contact with other cells
Contains channels, transporters, receptors, enzymes, cell-identity markers, and linker proteins
Mediates entry and exit of substances

Question 20

What is the Cytoplasm? And what is its Function?

Answer 20

Cellular contents between plasma membrane and nucleus:
Cytosol and Organelles

Function:
Site of all intracellular activities except those occurring in the nucleus

Question 21

What is the Organelles? And what is its Function?

Answer 21

Specialized structures with characteristic shapes

Function:
Each has a specific function

Question 22

What is the Cytoskeleton? And what is its Function?

Answer 22

Cytoskeleton is a network in the Cytoplasm composed of 3 protein filaments:
Microfilaments
Intermediate filaments
Microtubules

Function:
Maintain shape and general organization of cellular contents
Responsible for cell movements

Question 23

What is the Cytosol? And what is its Function?

Answer 23

Composed of water, solutes, suspended particles, lipid droplets, and glycogen granules

Function:
Fluid in which many of the cell’s reactions occur

Question 24

What is the Centrosome? And what is its Function?

Answer 24

Pair of Centrioles plus Pericentriolar Matrix

Function:
Pericentriolar Matrix contains tubulins, which are used for growth of the mitotic spindle and microtubule formation

Question 25

What is the Ribosome? And what is its Function?

Answer 25

Composed of 2 subunits containing ribosomal RNA and proteins
May be free in cytosol or attached to Rough Endoplasmic Reticulum

Function:
Protein synthesis

Question 25

What is the Cilia and Flagella? And what is its Function?

Answer 25

Motile cell surface projections that contain 20 microtubules and a basal body
Cilia: made of 9 doublets that have attached proteins called Dynein
And 2 central microtubules

Function:

Cilia: Move fluid across cell’s surface
Power stroke and Recovery stroke

Flagella: Move entire cell
Wave movement

Question 26

What is the Endoplasmic Reticulum? And what is its Function?

Answer 26

Membranous network of flattened sacs or tubules
Rough ER is covered by ribosomes and is attached to nuclear envelope
Smooth ER lacks ribosomes

Function:

Rough ER:
Synthesize glycoproteins and phospholipids that are transferred to cellular organelles, inserted into plasma membrane, or secreted during exocytosis

Smooth ER:
Synthesize fatty acids and steroids
Inactivate or Detoxify drugs
Remove phosphate group from glucose-6-phosphate
Store and Releases calcium ions in muscle cells

Question 27

What is the Golgi Complex? And what is its Function?

Answer 27

Consists of 3-20 flattened membranous sacs called cisternae
Structurally and functionally divided into Cis face (entry), medial cisternae, and Trans face (exit)

Function:

Cis Face:
Accepts proteins from Rough ER

Medial Cisternae:
Form glycoproteins, glycolipids, and lipoproteins

Trans Face:
Modifies molecules further
Then sorts and packages them for transport to their destinations

Question 28

What is the Lysosome? And what is its Function?

Answer 28

Vesicle formed by the Golgi Complex
Contains digestive enzymes

Function:
Fuses and digests contents from endosomes, phagosomes, and vesicles formed during bulk-phase endocytosis (pinocytosis)
Transports final products of digestion into cytosol
Digests worn-out organelles (Autophagy), entire cells (Autolysis), and extracellular materials

Question 29

What is the Peroxisome? And what is its Function?

Answer 29

Vesicle containing oxidases (oxidative enzymes) and catalases (decomposes hydrogen peroxide)
New peroxisomes bud from preexisting ones

Function:
Oxidizes amino acids and fatty acids
Detoxifies harmful substances such as hydrogen peroxide and associated free radicals

Question 30

What is the Proteasome? And what is its Function?

Answer 30

Tiny barrel-shaped structure that contains proteases (proteolytic enzymes)

Function:
Degrades unneeded, damaged, or faulty proteins by cutting them into small peptides

Question 31

What is the Nucleus? And what is its Function?

Answer 31

Consists of a nuclear envelope with pores, nucleoli, and chromosomes, which exist as a tangled mass of chromatin in interphase cells

Function:
Nuclear pores control the movement of substances between the nucleus and cytoplasm
Nucleoli produce ribosomes
Chromosomes consist of genes that control cellular structure and direct cellular functions

Question 32

What is the Mitochondrion? And what is its Function?

Answer 32

Consists of an external and an internal mitochondrial membrane, cristae, and matrix
New mitochondria from from preexisting ones

Function:
Site of aerobic cellular respiration that produces most of a cell’s ATP
Play an important early role in Apoptosis

Question 33

What is Transcription?

Answer 33

Transcription occurs in the nucleus and is the process by which genetic information encoded in DNA is copied onto a strand of RNA (mRNA) to direct protein synthesis

On DNA there’s Promoter, Gene, and Terminator
RNA Polymerase attaches to DNA on Gene
Build mRNA with Codons following DNA base triplets
New mRNA exits RNA Polymerase
Introns are snipped and deleted
Exons are spliced together
Functional mRNA exits through Nuclear pore into Cytoplasm

Question 34

What is Translation?

Answer 34

Translation occurs outside nuclear in cytoplasm
Translation is the process of reading the mRNA nucleotide sequence to determine the amino acid sequence of the newly formed protein

mRNA attached to small subunit of ribosome
Initiator tRNA attaches to start codon on mRNA
Large and small ribosomal subunits join to form functional ribosome
Initiator tRNA fits into P Site
Anticodon of incoming tRNA pairs with next mRNA codon at A Site
Amino acid on tRNA at P Site form peptide bond with amino acid on A Site
The 2-peptide protein created from the formation of peptide bond becomes attached to tRNA on A Site
Ribosome shifts by one codon, tRNA previously on P Site enters E Site and is released from ribosome, tRNA previously at A Site is now at P Site
Protein synthesis stops when ribosome reaches a stop codon on mRNA

Question 35

What is Replication of DNA?

Answer 35

DNA makes an exact copy of itself
DNA splits at Replication Fork
New strand is made out of each Old strand by DNA Polymerase
Forming 2 double helices made of one new and one old strand each

Question 36

What is Cell Division?

Answer 36

Process by which cell reproduce itself

Cell Cycle:
G1 Phase
S Phase
G2 Phase
Mitotic Phase - PMAT
Possible G0 Phase

Interphase = G1, S, and G2

Question 37

What is Mitosis?

Answer 37

Mitosis occurs when nucleus of cell divides
Results in distribution of 2 sets of chromosomes into 2 separate nuclei
Divided into 4 steps (PMAT):
Prophase
Metaphase
Anaphase
Telophase

Question 38

What is Prophase?

Answer 38

Chromatin condenses into chromosomes
Nuclear membrane disappears
Centrosomes move to opposite poles

Late Prophase:
Mitotic spindle (microtubules) form and attach to chromosomes at Kinetochore

Question 39

What is Metaphase?

Answer 39

Centromeres of chromosomes line up at the metaphase plate

Question 40

What is Anaphase?

Answer 40

Centromeres of chromosomes split
Sister chromatids move towards opposite poles of the cell

Late Anaphase:
Cleavage furrow forms

Question 41

What is Telophase?

Answer 41

Mitotic spindle dissolves
Chromosomes regain their chromatin appearance
New nuclear membrane forms

Question 42

What is Cytokinesis?

Answer 42

Cleavage furrow grows
Eventually cytoplasm of parent cell fully splits
Forming 2 identical cells

Interphase starts when this is complete

Question 43

What is Interphase?

Answer 43

Period between cell divisions
Chromosomes not visible under light microscope

Question 44

What is G1 Phase of Interphase?

Answer 44

Cell duplicates organelles
Replication of chromosomes begin
If stay too long called G0 Phase

Question 45

What is S Phase of Interphase?

Answer 45

Replication of DNA and centrosomes

Question 46

What is Mitotic Phase?

Answer 46

Parent cell produces identical cells with identical chromosomes
Chromosomes visible under light microscope

Question 47

How is Meiosis I Prophase I different than Mitosis?

Answer 47

Tetrads form by synapsis of sister chromatids of homologous chromosomes

Crossing-over between non-sister chromatids

Question 48

How is Meiosis I Metaphase I different than Mitosis?

Answer 48

Pairing of homologous chromosomes at metaphase plate instead of single chromosomes

Question 49

How is Meiosis I Anaphase I different than Mitosis?

Answer 49

Separation of homologous chromosomes instead of sister chromatids
(sister chromatids remain together here)

Question 50

How is Meiosis I Telophase I different than Mitosis?

Answer 50

2 non-identical cells formed

Question 51

What is Meiosis II?

Answer 51

Meiosis II looks similar to Mitosis, but results in 4 haploid cells that are non-identical

Question 52

What is the Resting membrane Potential?

Answer 52

1- K+ diffuses out of cell down their concentration gradient via leakage channels, making inner plasma membrane face negatively charged

2- K+ also moves into the cell because attracted to negatively charged inner plasma membrane face

3- Negative membrane potential (-90mV) established when K+ moving out equals K+ moving into cell

Question 53

How does Cell Communication work?

Answer 53

1- Ligand (1st messenger, could be neurotransmitter or hormone) binds to receptor
Receptor changes shape and activates

2- Activated receptor binds to a G protein and actives it
G protein changes shape and release GDP and bind to GTP (energy source)

3- Activated G protein activates or deactivates an Effector protein
Effector protein changes shape

4- Activated Effector enzymes catalyze reactions that produce 2nd messenger (like Cyclic AMP - cAMP, or Ca2+)

5- 2nd messenger activate other enzymes or ion channels
cAMP usually activates protein Kinase enzymes

6- Kinase enzymes activate other enzymes
Kinase enzymes transfer phosphate groups from ATP to specific proteins and activate a series of other enzymes that trigger various metabolic and structural changes in the cell

Question 54

What is a Microfilament?

Answer 54

Strands made of spherical protein subunits called Actin

Question 55

What is an Intermediate Filament?

Answer 55

Tough, insoluble protein fibers constructed like woven ropes composed of Tetramer (4) Fibrils

Question 56

What is a Microtubule?

Answer 56

Hollow tubes of spherical protein subunits called Tubulin