Chapter 3 - Cellular Level

Question 1

Define cell and list the 3 major components

Answer 1

Cell: living structural and functional unit enclosed by a membrane divided into 3 main parts:

1. Plasma membrane: separates the cells internal membrane from the external environment
2. Cytoplasm: consists of cytosol (ICF) and organelles
3. Nucleus: a large organelles that contains chromosomes (single DNA molecule) with thousands of genes

Question 2

What is the fluid-mosaic model?

Answer 2

The molecular arrangement of the plasma membrane resembles a continually moving sea of fluid lipids that contain a mosaic of different proteins

Question 3

What are the 4 functions of the plasma membrane?

Answer 3

1) Acts as a barrier separating inside or outside of cell
2) Controls the flow of substances into and out of cell
3) Helps identify the cell to other cells (eg immune cells)
4) Participates in intercellular signalling

Question 4

Describe the basic structure of the lipid bilayer

Answer 4

2 back-to-back layers made up of 3 types of lipid molecules: Phospholipids, cholesterol, and glycolipids

Question 5

How do phospholipids orient themselves in the lipid bilayer?

Answer 5

They are amphipathic

Hydrophilic heads face outward and hydrophobic fatty acid tails in each half of the bilayer point toward one another forming a nonpolar hydrophobic region

Question 6

Integral vs. peripheral proteins

Answer 6

Integral: extend into or through the lipid bilayer (most are transmembrane)

Peripheral: not as firmly embedded - attached to the polar heads of phospholipids or integral proteins

Question 7

Define glycoprotein and glycocalyx

Answer 7

glycoprotein: integral proteins with C groups that protrude into the ECF

Carbohydrate portions form an extensive sugary glyccalyx that enables cells to recognize one another

Question 8

What are the functions of membrane proteins? (ion, carrier, receptor, enzyme, linker, cell-identity)

Answer 8

Ion channels (integral): forms pore that specific ions can flow through

Carriers (integral): transports specific substances across membrane by undergoing a change in shape

Receptors (integral): Recognizes specific ligand (molecule that binds to receptors) and alters cell’s function in some way

Enzymes (integral & peripheral): catalyze specific chemical reactions

Linkers (integral & peripheral): Anchor filaments inside and outside membrane, providing stability and shape for cell

Cell-identity markers (glycoprotein): distinguishes you cells from anyone else’s and recognize and respond to potentially dangerous foreign cells

Question 9

Describe membrane permeability

Answer 9

Highly permeable to non-polar molecules
Moderately permeable to small, polar uncharged molecules
Impermeable to ions and large, uncharged polar molecules

The more hydrophobic or lipid-soluble, the greater permeability

Question 10

Concentration vs. Electrical gradient (membrane potential)?

Answer 10

Concentration: difference in the concentration of a chemical from one place to another

Electrical: inner surface of the plasma membrane is more negatively charged & the outer surface is more positively charged. This difference in electrical charge is called an electrical gradient. Since it is across a membrane it is termed the membrane potential.

Question 11

What’s the electrochemical gradient?

Answer 11

The combined influence of the concentration gradient and electrical gradient is the electrochemical gradient.

A substance will move downhill from where it’s more concentrated to where it’s less concentrated to reach equilibrium. A positively charged substance will move towards a negatively charged substance and vice versa.

Question 12

Passive vs. active transport across a membrane?

Answer 12

Passive: substance moves down its gradient using only its own kinetic energy (energy of motion)

Active: cellular energy is used to drive the substance ‘uphill’ against its gradient (ATP or using vesicles)

Question 13

WHat is diffusion?

Answer 13

A passive process in which random mixing of particles occurs in a solution because of the particles’ kinetic energy.

Both solutes and solvents undergo diffusion. Solute molecules will diffuse towards an area of low concentration and eventually they become evenly distributed and reach equilibrium

Question 14

5 Factors that influence the diffusion rate of substances across a membrane

Answer 14

Steepness of concentration gradient: greater steepness, faster diffusion

Temperature: higher temp, faster diffusion

Mass of the diffusing substance: the larger the mass the slower the diffusion

Surface area: larger SA, faster diffusion rate

Diffusion distance: greater distance, slower diffusion

Question 15

What is simple diffusion? Which molecules use this process?

Answer 15

Passive process. Substances move freely through the lipid bilayer without the help of membrane transport proteins.

Non-polar, hydrophobic molecules (O, CO2, N gases, steriods, fatty acids, fat soluble vitamins, small uncharged polar molecules like water and urea) pass via simple diffusion

Question 16

What is facilitated diffusion?

Answer 16

An integral membrane protein (either channel or carrier) assists a specific substance across a membrane. Usually solutes that are too polar or highly charged

Question 17

What’s channel-mediated facilitated diffusion?

Answer 17

A solute moves down its concentration gradient across the lipid bilayer through a membrane channel (likely an ion channel)… passage of small inorganic molecules too hydrophilic to penetrate the nonpolar interior of the lipid bilayer

Question 18

What’s a gated channel?

Answer 18

When a part of the channel acts as a gate or a plug, changing shape in one way to open to pore and another to close

Question 19

What’s carrier-mediated facilitated diffusion?

Answer 19

A carrier moves a solute down its concentration gradient across the plasma membrane. Solute binds to specific carrier on one side of membrane and is released on other side. The rate of carrier mediated diffusion is determined by the steepness of the concentration gradient across the membrane.

Question 20

What is the transport maximum?

Answer 20

Once all carriers are occupied the transport maximum is reached, exhibiting saturation (like a sponge)

Question 21

Define osmosis. What are the two ways water molecules pass through the membrane

Answer 21

Type of diffusion in which there is net movement of a solvent through a selectively permeable membrane; only occurs when membrane is permeable to water but not certain solutes

1. By moving between neighbouring phospholipid molecules in the lipid bilayer via simple diffusion
2. By moving through aquaporins, integral membrane proteins that function as water channels

Question 22

Discuss the principles of osmosis using a U-shaped tube

Answer 22

Water is poured into the left and a solute solution is poured into the right

Water moves into the right tube (down its concentration gradient)

The membrane prevents diffusion of the solute so the volume increases in the right leading to hydrostatic pressure

Hydrostatic and osmotic pressure forces the water back into the left until equilibrium is reached

Question 23

Hydrostatic vs. osmotic pressure

Answer 23

Hydrostatic: pressure from the increased volume forces water back from where it came

Osmotic: pressure exerted from the impermeable solute (the higher the solute concentration, the higher the pressure)

Question 24

What is Tonicity?

Answer 24

As water moves by osmosis, their volume increases or decreases

Tonicity is a measure of the solution’s ability to change the volume of cells by altering their water content.

Question 25

Isotonic vs. hypotonic vs hypertonic solution

Answer 25

Isotonic: Any solution in which a cell maintains its normal shape and volume

Hypotonic: Solution with lower concentration of solutes than the than the cytosol causing water molecules to enter faster than they leave (swell & burst - hemolysis)

Hypertonic: Solution with higher concentration of solutes than the cytosol causing water molecules to leave the cells faster then they enter (shrink - crenation)

Question 26

What is Active transport?

Answer 26

Energy required for carrier proteins to move solutes across the membrane against their concentration gradient.

Question 27

WHat are the 2 sources of cellular energy to drive ACTIVE TRANSPORT?

Answer 27

1) energy obtained from the hydrolosys of ATP (Primary active transport)
2) Energy stored in an ionic concentration gradient (secondary active transport)

Question 28

What is Primary Active Transport?

Answer 28

Energy derived from hydrolysis of ATP changes the shape of a carrier protein which “pumps” a substance across a plasma membrane against its concentration gradient

Question 29

Describe the sodium-potassium pump?

Answer 29

3 Na+ ions from the cytosol bind to the inside of the Na-K pump

Na+ binding triggers ATP to be split into ADP + P and the energy causes a shape change, expelling the 3 Na+ ions

2 K+ ions from the ECF bind to pump and cause P to be released into the cytosol

P release causes shape change, moving 2 K+ into the cell

Question 30

What is secondary active transport?

Answer 30

They use energy stored in an ionic concentration gradient (Na+ or H+), indirectly consuming ATP obtained in primary active transport pumps

Question 31

Antiporters vs. symporters

Answer 31

Secondary active transport mechanisms

Antiporters carry two substances across the membrane in opposite directions

Symporters carry two substances across the membrane in the same direction

Question 32

What are the 3 types of endocytosis?

Answer 32

receptor-mediated endocytosis, phagocytosis, and bulk-phase endocytosis

Question 33

What are the 6 steps of receptor-mediated endocytosis?

Answer 33

1) BINDING: A ligand binds to receptor on the membrane forming a receptor-LDL complex within a clathrin-coated pit tirggering invagination (fold inward)
2) VESICLE FORMATION: The invaginated edges fuse and a small piece of membrane pinches off
3) UNCOATING: vesicle loses its clathrin coat
4) FUSION WITH ENDOSOME: Uncoated vesicle fuses with endosome (within the endosome the LDL particles separate from the receptors)
5) RECYCLING OF RECEPTORS TO PLASMA MEMBRANE: Receptors are put into vesicles and returned the membrane
6) DEGRADATION IN LYSOSOMES: Vessicles holding LDL particles bud off endosome and fuse with a lysosome. Digestive enzymes break down the large protein and lipid molecules of LDL particle into amino acids, fatty acids, and cholesterol. These smaller molecules leave the lysosome.

Question 34

Define Phagocytosis and describe the process

Answer 34

A form of endocytosis in which phagocytes (macrophages and neutrophils)engulfs large solid particles (worn-out cells, bacteria, viruses etc.)

A particle binds to a receptor on the phagocyte causing it to extend pseudopods (projections of its plasma membrane and cytoplasm). Pseudopods surround the particle outside the cell and fuse to form a phagosome (vesicle), which enters the cytoplasm. Phagosome fuses with lysosomes and lysosomal enzymes break down injested material

Any undigested material remain indefinitely in a residual body vesicle

Question 35

Define bulk-phase endocytosis

Answer 35

aka pinocytosis: form of endocytosis in which tiny droplets of ECF are taken up

Membrane invaginate, taking ECF, forming a vesicle. The vesicle fuses with a lysosome where enzymes degrade the solutes

Question 36

Describe exocytosis

Answer 36

Secretory vesicles bind with the membrane and release their confects into the ECF

Question 37

Describes transcytosis

Answer 37

Vesicles undergo endocytosis on one side of the cell, move across the cell, and then undergo exocytosis on the opposite side

Question 38

What are the functions of cytoskeleton? What are the 3 types of filaments that contribute to its structure?

Answer 38

A network of protein filaments that extends throughout the cytosol to 1) help determine a cells shape and 2) aid movement of organelles within the cell

1. Microfilaments: thinnest elements that generate movement and provide mechanical support ; anchor cytoskeleton to integral proteins; support microvilli
2. Intermediate filaments: found in areas of mechanical stress; help to stabilize the position of organelles
3. Microtubule: largest element comprised of tubular that help determine cell change and function in the movement of organelles

Question 39

Describe the structure and function of the centrosome (organelle)

Answer 39

Located near the nucleus, consists of a pair of centrioles (cyndrical structures arranged in a circle) and pericentriol material (hundreds of ring-shaped tubulin complexes)

Functions: pericentriolar material builds microtubules in non-diviimd cells are forms the mitotic spending during cell division

Question 40

Describe the structure and function of the cilia and flagella (organelle)

Answer 40

Cilia: short hair-like projections that extend from the surface of the cell that move fluids along

Flagella: similar in structure but must longer and moves in a wavelike pattern to move an entire cell (sperm cell)

Question 41

Describe the structure and function of the ribosome (organelle)

Answer 41

Sites of protein synthesis that structurally consists of 2 subunits: large subunit and small subunit

Ribosomes associated with the ER synthesize proteins destined for insertion in the membrane or secretion from the cell

Free ribosomes synthesize proteins used in the cytosol

Question 42

Describe the structure and function of the endoplasmic reticulum (rough vs. smooth) (organelle)

Answer 42

The ER is a network of membranes in the form of flattened sacs that extends from the nuclear envelope and projects throughout the cytoplasm

Rough ER: continuous with the nuclear membrane and studded with ribosomes; synthesizes glycoproteins and phospholipids that are transferred into cellular organelles

Smooth ER: extends from the rough ER to form a network of membrane tubules; syntheses fatty acids and steroids, inactivates/dtoxifies harmful substances in liver, allows free glucose to enter bloodstream, and stores & releases Ca2+ which triggers muscle contraction

Question 43

Describe the structure and function of the golgi complex (organelle)

Answer 43

Proteins synthesized by the ribosomes on the rough ER are transported to other cells - the first step is through the Golgi complex which cnonists of 3-20 cisternae (small, flattened sacs that are curved and stacked like a pita)

Question 44

Describe the process of proteins passing through and exiting the golgi complex though maturation of the cisterna

Answer 44

1. proteins are syntheized by ribsomes on the right ER and pacakaged into transport vesicles
2. Transport vesicles crreate the entry face of the golgi complex and release proteins into its lumen (space)
3. Proteins move from the entry face into one or more medial cisterna where enzymes modify proteins into glycoproteins/glycolipids and lipoproteins
4. Products of the medial cisterna move into the lumen of the exit face where they are further modified, sorted, and packaged
5. Some proteins leave the exit face via secretory vesicles which deliver the proteins to the plasma membrane for exocytosis; some leave via membrane vesicles where they are incorporated into the membrane; others leave via transport vesicles that will carry proteins to another destination

Question 45

Describe the structure and function of a lysosome (organelle)

Answer 45

Membrane-enclosed vesicles that form the golgi complex - contain as many as 60 types of digestive and hydrolytic enzymes

They digest substances that enter via endocytosis & transport final products into cytosol; carry out autophagy; carry out autolysis (destruction of pathological cells)

Question 46

Describe the structure and function of a peroxisome (organelle)

Answer 46

aka microbodies contain several oxidases (oxidative enzymes) that remove H atoms from organic substance and oxidize toxic substances

They are abundant in the liver and contain an enzyme catalase that decomposes hydrogen peroxide - without these by-products of metabolism would cause cellular death

Question 47

Describe the structure and function of a proteasome (organelle)

Answer 47

tiny barrel-shaped structure that contains proteases (proteolytic enzymes) that break down unneeded, damaged, or faulty proteins

Question 48

Describe the structure and function of a mitochondrion (mitochondria) (organelle)

Answer 48

It is a site of aerobic cellular respiration reactions that produce most of a cell’s ATP

A mitochondrion consists of an outer and inner mitochondrial membrane (inner consists of folds called mitochondrial cristae) with a small fluid space in between (cavity enclosed by the mitochondrial matrix)

They play an important role in apoptosis - release cytochrome C that initiates a cascade that brings about apoptosis

Question 49

Describe the nucleus and the following components:

• nuclear envelope
• nuclear pore
• nucleolus
• gene
• chromatin & nucleosome
• genome
• chromatid

Answer 49

Nucleus: spherical shaped structure within a cell

Nuclear envelope: a double membrane that separates the nucleus from the cytoplasm (both membranes are lipid bilayers

Nuclear pore: openings in the nuclear envelope that are 10x size of a channel protein that allows passive diffusion of small ions and molecules

Nucleolus (nucleoli): spherical clusters of protein, DNA, and RNA not enclosed in a membrane that are the site of rRNA synthesis

Gene: control cellular structure and direct cellular activity which are arranged along 23 pairs of chromosomes

Chromatin: long large molecule of DNA that is coiled together

Nucleosome: Chromatins have a bead-on-a-string structure - each bean is a nucleosome that consists of a double-stranded DNA wrapped around a histone

Genome: total genetic info carried in a cell

Chromatids: Just before a cell divides the DNA replicates and the loops condense even more forming a pair of chromatids

Question 50

Describe the basic sequence of events that occurs in protein synthesis (proteome)

Answer 50

Proteome refers to all of an organisms proteins

In the process of gene expression, a genes DNA is used as a template for synthesis of a specific protein via transcription & translation

Transcription: in the nucleus, the genetic info of the base triplets in DNA serve as a template for coping the info into a complementary sequence codon

Translation: nucleotide sequence in mRNA molecule specifies the amino acid sequence of a protein

Question 51

Somatic vs. Reproductive cell division

Answer 51

Cell division is the process by which cells reproduce themselves - there are 2 types:

Somatic: undergoes a nuclear division called mitosis and a cytoplasmic division called cytokinesis to produce genetically identical cells

Reproductive: the mechanism that produces gametes, cells needed for generation of sexually reproducing organisms

Germ cells are gametes (sperm or oocyte) and a somatic cell is any cell in the body that is not a gem cell

Question 52

Describe the steps in transcription (gene expression)

Answer 52

Enzyme RNA polymerase attaches to the beginning of gene and catalyzes transcription

Bases pair in a complementary patterns (A=U, T = A, G=C, C=G)

Transcription ends at a special nucleotide called a terminator and RNA detaches

The mRNA product then passes through a nuclear pore into the cytoplasm, where translation takes place

Question 53

Describe the steps in translation (gene expression)

Answer 53

Ribosomes carry out translations: the small subunit has a binding site for mRNA and the larger subunit has 3 binding sites for tRNA (P, A, E)

1. Initiator tRNA attaches to start codon
2. Large & small ribosomal subunits join to form a functional ribosome and initiator tRNA fits into P site
3. Anticodon of incoming tRNA pairs with the next mRNA codon at A site
4. Amino acid on tRNA at P site forms a peptide bond with amino acid at A site
5. The 2-peptide protein created from the formation of the peptide bond becomes attached to tRNA at the A site
6. Ribosome shifts by one codon: tRNA at P enters E site and is released; tRNA at A site is now at P site
7. Protein synthesis stops when the ribosome reaches stop codon on mRNA

Question 54

List cell cycle in somatic cells

Answer 54

Interphase (G1, S, G2 phase) -> Mitotic phase (prophase, metaphase, anaphase, telophase) -> Cytokinesis

Question 55

Describe the events in interphase of somatic cells

Answer 55

Interphase: cell replicates; consists of 3 phases:

G1 phase (8-10hr): Metabolically active cell duplicates most of its organelles and cytosolic components replication of chromosome begins

S phase (~8hr): Replication of DNA and centrosomes

G2 phase: cell growth, enzyme and protein synthesis continue; replication of centrosomes complete

Question 56

What is G0 phase?

Answer 56

Cells that remain in G1 for a very long time and said to be in the G0 phase – most nerve cells are in the G0 phase

Question 57

Describe the events in the mitotic phase of somatic cells

Answer 57

Mitotic phase: parent cell produces identical cells and consist of nuclear division and cytoplasmic division

Nuclear division: occurs in 4 stages:
1) Prophase: chromatin fibers condense into paired chromatids (held by centrosome); nucleolus and nuclear envelope disappear; each centrosome moves to an opposite pole of the cell

2) Metaphase: centromeres of chromatid line up at the metaphase line
3) Anaphase: centromeres split; identical sets of chromosomes move to opposite poles of cell
4) Telophase: nuclear envelopes and nucleoli reappear; chromosomes resume chromatin form; mitotic spindle disappears

Cytoplasmic division (cytokinesis): contractile ring forms cleavage furrow around centre of cell, dividing cytoplasm into separate and equal portions

Question 58

When does cytokinesis begin?

Answer 58

In late anaphase when the formation of a cleavage furrow, a slight indentation of the plasma membrane, and is completed after telophase

Question 59

Discuss the stages in reproductive cell division

Answer 59

Interphase - diploid cells starts to replicate and as a result consists of 2 sister chromatids

Meiosis occurs in 2 successive stages: meiosis I and meiosis 2

Meiosis 1 begins once chromosomal replication is complete and consists of 4 phases:

1) Prophase I: sister chromatids pair off resulting in four chromatids which synapse to form a structure called a tetrad - parts of the chromatids may be exchanged either with homologous chromatids or non-sister (crossing-over)
2) Metaphase I: tetrads line up along the metaphase plate
3) Anaphase I: Homologous chromosome separate (sister chromatids remain together)
4) Telophase I: each cell has one of the replicate chromosomes from each homologous pair of chromosomes

Meiosis II also konstis of 4 phases - each of the haploid cells formed during meiosis I divides; the result being 4 haploid gametes that are genetically different from the starting cell

Question 60

Describe how cells differ in size and shape

Answer 60

Cell size is measured by micrometers and cells vary drastically

Shapes of cells also vary considerably and the shape is related to function