Chapter 6 - A tour of the Cell

Question 1

How do light microscopes work

Answer 1

use visible light and glass lenses to magnify and project images
- The lenses refract the light in a way that the image is magnified
- Allows us to study living cells
- Been revitalized recently by the addition of fluorescent markers and super resolution microscopy

Question 2

Parameters in Microscopy

Answer 2

• Magnification: the ratio of an objects image size to its actual size
  • Resolution: the clarity of the image; the minimum distance two points can be separated by and still be distinguished as separate points
    ○ Have a resolution of about 0.2 um
  • Contrast: the difference in brightness between the light and dark areas of an image
    ○ Enhanced through staining

Question 3

Electron Microscope

Answer 3

focuses a beam of electrons through the specimen or onto its surface for higher resolution imaging
- In order to prepare the specimen, it often leads to cells being killedT

Question 4

Types of EM

Answer 4

• Scanning Electron Microscopes: Scans the surface of the sample which excites electrons, which these secondary electrons are then detected by a device which translates the electrons into an image of the specimen’s surface which appears to be 3d
  ○ especially useful for the detailed study of the topography of a specimen
• Transmission Electron Microscope: aims an electron beam through a thin section of the specimen, which has been stained with atoms of heavy molecules and have attached to cellular structures, creating an image of the internal structure of cells
  ○ A new type was developed called Cryo-electron Microscopy which allows specimens to be preserved at extremely low temperatures, which allows visualization of structures in their cellular environments

Question 5

Cell Fractionalization

Answer 5

a technique for determining cell structure and function by taking cells apart and separating major organelles and other subcellular structures

• Requires a centrifuge which spins the disrupted cells, while differential centrifuge separates components based on their size
  ○ At faster speeds, the smaller the components form the supernatant, at slower speeds, the pellets consist of larger components

Question 6

Parts of an Animal Cell

Answer 6

• Nucleus:
  ○ Nuclear envelope:
  ○ Nucleolus:
  ○ Chromatin:
  
  • Endoplasmic Reticulum:
  • Cytoskeleton:
  • Mitochondria:
  • Lysosomes:
  • Golgi Apparatus:

Question 7

Parts in a Plant Cell

Answer 7

• Nucleus
  ○ Nuclear Envelope
  ○ Nucleolus
  ○ Chromatin
  
  • Rough ER and Smooth ER
  • Golgi Apparatus
  • Mitochondrion
  • Plasma Membrane
  • Cell Wall:
  • Plasmodesmata:
  • Chloroplasts:
  • Cytoskeleton
    Central Vacuole

Question 8

Nucleus

Answer 8

contains the genetic material in the form of chromosomes in eukaryotic cells
- Directs protein synthesis and is enclosed by the nuclear envelop which is a lipid bilayer with perforated pores

Question 9

Nuclear Lamina

Answer 9

lines the nuclear envelope besides at the pores and is a network array of protein filaments which maintain the shape by mechanically supporting the envelope
- Assisted by the nuclear matrix which extend throughout the nuclear interior
- Both help organize genetic material so it functions effectively

Question 10

Nucleolus

Answer 10

a structure in the nucleus consisting of chromosomal regions containing and synthesizing rRNA molecules as well as assembling Ribosomes
- Can be two or more depending on species and stage of cells reproductive life cycle

Question 11

Ribosomes

Answer 11

complexes made of rRNA and proteins which carry out protein synthesis
- Not considered organelles and lack a membrane

• can either be free floating in the cytosol and create proteins that function in the cytosol
  
  • Can also be bound ribosomes which create proteins destined for membrane insertion, organelle packaging and secretion

Question 12

Endomembrane system:

Answer 12

carries out protein synthesis, protein transport in and around the membrane and organelles, the metabolism and movement of lipids as well as detoxification of poisons
- Membranes are connected either physically or through vesicular transfer

Includes:
- nuclear envelope,
- endoplasmic reticulum,
- golgi apparatus,
- lysozomes,
- various type of vesicles and vacuoles
- plasma mebrane

Question 13

Endoplasmic Reticulum

Answer 13

an extensive network of membranes that are called cisternae
- its a membrane which separates the internal compartment known as the lumen/cisternal space from the cytosol

• both smooth and rough ER

Question 14

Function of Smooth ER

Answer 14

• Important in synthesizing lipids, including oils, steroids and new membrane phospholipids
• help detoxify drugs and poisons by usually adding hydroxyl groups to drug molecules making them more water soluble and able to be flushed out
• stores calcium ions in the ER lumen of muscle cells

Question 15

Functions of RER

Answer 15

• Synthesizes and secretes proteins such as glycoproteins; proteins with carbohydrates covalently bonded to them
• Is a membrane factory for the cell and grows by adding membrane proteins and phospholipids to its own membrane

Question 16

Golgi Apparatus

Answer 16

consists of stacks of flat membranous sacs that modify, store and route products of the ER(proteins)
- Extensive in cells specialized for secretion
- Has distinct cis and tran faces for the membranous stacks which are respectively the receiving and secreting sides
○ Cis means same side, referring to the same side as ER

Question 17

Functions of the GOlgi

Answer 17

• Products which pass through the golgi are modified in the transit from cis to tran sides
  • Golgi also manufactures molecules like polysaccharides
  • Involved in sorting and exporting of molecules by tagging them to direct where they go in or out of the cell through vesicles

Question 18

Cisternal Maturation Model

Answer 18

states the cisternae progress forward from cis to trans regions, carrying and modifying molecules as they move
- Reality may be that there is movement in the outer regions while the inner remains still

Question 19

Lysosomes

Answer 19

membranous sac of hydrolytic enzymes which many eukaryotic cells use to hydrolyze macromolecules
- Excessive leakage from large number of lysosomes can destroy a cell by self-digestion, 1 breaking down will not
- Created by the rough ER and transferred to the Golgi for processing

Question 20

Process of Lysosome Digestion

Answer 20

• Phagocytosis:
  ○ engulf smaller organisms which allows the food vacuole to be fused to a lysosome
  ○ Enzymes digest the food and products such as sugars, amino acids pass into the cytosol
  • Autophagy: cell renewal/recycling
    ○ a damaged organelle, becomes surrounded by a double membrane which a lysosome then fuses with
    ○ Lysosome enzymes dismantle the inner membrane and enclosed material resulting in small organic compounds being released into the cytosol for reuse

Question 21

Lysosome Storage Disease

Answer 21

when hydrolytic enzymes are lacking leading to the accumulation of indigestible material and interferences with cellular activities

Question 22

Vacuoles

Answer 22

large vesicles derived from the endoplasmic reticulum and golgi apparatus which has specialized functions in different cells
- Have elective membranes which transport solutes

Types:
- food vacuoles
- contractile vacuoles
- hydrolytic vacuoles
- central vacuoles

Question 23

Mitochondrion

Answer 23

the sites of cellular respiration which uses oxygen to drive the production of ATP by extracting energy from bonds between sugars, fats and other fuels

• Found in nearly all eukaryotic cells including plant and fungi cells
• The number of mitochondria’s in a cell directly correlates with the cell levels metabolic activity
  Can move around, change shape and fuse and divide into fragments; it’s a dynamic organelle

Question 24

Structure of Mitochondrion

Answer 24

• Each of the two membranes enclosing are phospholipid bilayers with unique collections of embedded proteins

inner foldings called cristae which due to their folding, give the inner membrane a large surface area, enhancing its productivity of cellular respiration

• Intermembrane space is the narrow region between the inner and outer membrane
• Mitochondrial matrix is enclosed by the inner membrane which contains many different enzymes as well as mitochondrial DNA and ribosomes

Question 25

Chloroplasts

Answer 25

- Chloroplast: found in plants and algae, are the site of photosynthesis which converts solar energy to chemical energy by absorbing sunlight and using it to synthesis sugars from Co2 and water. - Contain chlorophyl, and other enzymes and molecules associated with the photosynthetic production of sugar - dynamic in behavior like mitochondria

Question 26

Structure of Chloroplasts

Answer 26

- The contents are partitioned from the cytosol by an envelope consisting of two membranes, separated by a narrow intermembrane space - Inside the membranous system are thylakoids in the form of flattened, interconnected sacs which can be stacked into granums and contain chlorophyl pigments - The fluid outside the thylakoids is the stroma which contains Chloroplast DNA as well as ribosomes and enzymes

Question 27

Peroxisomes

Answer 27

a single membrane which contain enzymes that remove hydrogen atoms from various substrates and transfer oxygen - Creates hydrogen peroxide(H2O2) which in itself is toxic, but the organelle contains an enzyme which converts it to water - detoxifies in the liver - uses oxygen to break down fatty acids as fuel for cellular respiration

Question 28

Cytoskeleton

Answer 28

a network of fibers extending throughout the cytoplasm and serve a variety of mechanical, transport and signaling functions - Prokaryotes also have similar cytoskeletons made up of proteins - Made up of 3 fibres; microtubes, microfilaments, intermediate filaments

Question 29

Functions of Cell Cytoskeleton: Support

Answer 29

- The most obvious function of the cytoskeleton is to give mechanical support to the cell and to maintain its shape - Especially important for animal cells which lack cell walls - Provides anchorage for other organelles and cystolic enzymes. - Extremely dynamic and can be quickly dismantled and set up in a new location, changing the shape of the shell

Question 30

Functions of Cytoskeleton: Cell Motility

Answer 30

the interaction with Motor Proteins to induce changes in cell location and the movement of cell parts - Outside the cell, cytoskeletal elements and motor proteins work to move whole cells - Inside the cell, vesicles use motor proteins 'feet to walk' along a track provided by the cytoskeleton.

Question 31

Components of the cytoskeleton

Answer 31

Microtubules:a hollow rod composed of tubulin proteins which make up part of the cytoskeleton in all eukaryotic cells - grow in length by adding tubulin dimers and can be disassembled when needed Microfilaments: a twisted double chain of actin proteins which make up the cytoskeleton and work with myosin to cause cell contractions - Can occur as linear or form structural networks when it binds with certain proteins - Structural role is to bear tension Intermediate Filaments: found in the cell of animals and made of keratin proteins coiled together which are specialized for bearing tension and are more permanent - Intermediate in size between Microtubules and microfilaments

Question 32

Function of Microtubules

Answer 32

- Support and shape the cell and serve as tracks with motor proteins can move along - Guide vesicles from the ER to the Golgi and from the Golgi to the Plasma membrane - Involved in the separation of chromosomes during cell division

Question 33

Function of Microfilaments

Answer 33

-help support the cells cortex; shape -They are known for their role in cell motility: - actin and myosin filaments interact to cause contractions of muscular cells - In some white blood cells and protists, actin and myosin are also involved in movement of cells which crawl along surfaces through pseudopodia - In plant cells, actin-protein interactions contribute to cytoplasmic streaming

Question 34

Function of Intermediate Filaments

Answer 34

- Sturdy and play a role in reinforcing the cell shape - fixesand achors the position of organelles and nucleus

Question 35

Cilia

Answer 35

Cilia: a short appendage containing microtubules - Usually occur in large numbers on cell surface

Question 36

Types of Cilia

Answer 36

- Motile cilia are specialized for locomotion or moving fluid past the cell - Formed from a core of 9 outer doublet microtubules and two inner single microtubules unsheathed in an extension of the plasma membrane(9+2 arrangement) - Primary cilium are non-motile and are arranged in a 9+0 arrangement acting as a single receiving antenna

Question 37

Dyneins

Answer 37

found in cilia and flagella it’s a large motor protein extending between microtubule doublets with ATP hydrolysis driving the changes in dynein shape leading to the bending of cilia and flagella - Typically has 'two feet' with one attached while the other reattaches one step further

Question 38

Cell Wall

Answer 38

a protective layer external to that of the plasma membrane which protects the cell, maintains its shape and prevents excessive uptake of water

Question 39

process of developing a cell wall

Answer 39

- Originally a young plant cell secretes a primary cell wall; a relatively thin and flexible wall which is glued to adjacent primary cell walls by the middle lamella - When the cell stops growing some strengthen its wall by secreting hardening substances while others create a secondary cell wall; often deposited in several laminated layers with a strong and durable matrix that affords cell protection and support

Question 40

Extracellular Matrix

Answer 40

the meshwork surrounding animal cells consisting of glycoproteins, polysaccharides and proteoglycans - Super important in regulating cell life by communicating through integrins - Can influence the activity of genes in the nucleus through chemical and mechanical signals - Can coordinate the behavior of all cell tissue through triggering signaling pathways and changing the set of proteins

Question 41

Cell Junctions in Plants

Answer 41

- Plasmodesmata: an open channel through the cell wall which connect the cytoplasm of adjacent cells allowing the transfer of water, small solutes and larger molecules to pass through - Appear to move through with the help of the cytoskeleton

Question 42

Types of Junctions in Animal Cells

Answer 42

- Tight Junctions: prevents the leakage of material through the space between cells - Desmosomes: functions as rivet, fastening cells together - Gap Junctions: consisting of proteins surrounding a pore allowing the passage of materials between cells which are similar to plasmodesmata however they are not lined with a membrane