The Cell

Question 1

Describe the importance of microscopy in the study of cellular biology

Answer 1

Microscopes are used to examine microorganisms in cellular biology and to study cells themselves and how they function in a living organism

Question 2

Describe the role of cells in organisms

Answer 2

-Provide structure and support for the body
-Facilitate growth through mitosis
-Take in nutrients from food and convert those nutrients into energy
-Carry out specialized functions
-Contain the body’s hereditary material and can make copies of themselves.

Question 3

Discuss the 3 principles of cell theory

Answer 3

Cell Theory:
-The cell is the basic unit of life
-All organisms are made of one or more cells
-All cells arise from pre-existing cells, “Omnis Cellula e Cellula”

Therefore, all cells today represent a continuous line of descent from the first living cells

Question 4

Describe factors that limit cell size

Answer 4

-Most cells are relatively small due to reliance on diffusion of substances in and out of cells

-As the cell increases in size, its surface area-to-volume ratio decreases. (^2 vs ^3)

-The cell will either divide or die to minimize volume and maximize surface area.

-Cells must have a high surface area to volume ratio to maintain homeostasis

Question 5

Rate of cellular diffusion affected by

Answer 5

-Surface area available
-Temperature
-Concentration gradient
-Distance
-Size of diffusing substance

Question 6

Categorize structural and functional similarities in cells

Answer 6

-Protein synthesis
-Cytoplasm
-Ribosomes
-Plasma membrane (phospholipid bilayer)

Question 7

Describe the organization of prokaryotic cells

Answer 7

-Circular DNA present in the nucleoid
-Ribosomes
-Cytosol
-Plasma membrane
-Cell wall: contains peptidoglycan
-Capsule: Mediates adherence of bacteria to particular surfaces. Capsules are known to protect bacteria from engulfment by predatory phagocytes and from attack by antimicrobial agents
-Fimbriae: extensions of the plasma membrane; involved in attachment to surfaces; major determinants of bacterial virulence because they allow cells to attach to tissues and to resist attack by phagocytic white blood cells
-Pilus: mainly function in gene transfer
-Flagellum

Question 8

Describe eukaryotic cells

Answer 8

-Eukaryotic cells are bigger and more complex
-Possess a membrane bound nucleus
-Hallmark is cellular compartmentalization achieved through membrane bound organelles and the endomembrane system
-Genome consists of several linear chromosomes

Question 9

Use the fluid mosaic model to describe the structure of the plasma membrane

Answer 9

A mosaic of proteins floats in or on the fluid lipid bilayer like boats on a pond.

Question 10

Discuss the structure and function of the nucleus in eukaryotic cells

Answer 10

Structure:
-Nucleolus: region where rRNA synthesis takes place
-Chromatin: DNA plus associated proteins
-Nuclear envelope separates the nucleoplasm from the cytoplasm and has 2 phospholipid bilayers
-Nuclear pores control passage of materials in and out

Function:
The nucleus keeps eukaryotic DNA molecules organized and separated from cytoplasm. Therefore, it controls all cell activities.

Question 11

Describe structure of ribosomes and their role in protein synthesis

Answer 11

Structure:
Ribosomes are catalytic and made up of a large subunit (top) and small subunit (bottom). Made of RNA and protein. They can be found in the cytooplasm or bound to the ER.

Function:
During protein synthesis, ribosomes assemble amino acids into proteins. Where protein synthesis occurs!!

Question 12

Describe the structure and function of the chloroplast

Answer 12

Structure:
-Present in all cells of plants and some other eukaryotes
-Contain the green pigment chlorophyll
-2 membranes
-Thylakoids are membranous stacks that form grana

Function:
Photosynthesis

Also:
Mitochondria and chloroplast are complimentary. The products of respiration are the reactants of
photosynthesis and vice versa

Question 13

Explain the probable origin of chloroplasts

Answer 13

Endosymbiotic Theory: Postulates that chloroplasts and mitochondria used to be prokaryotic cells that became trapped in evolving eukaryotic cells

Evidence:
-Mitochondria and ribosomes reminiscent of prokaryotic cells
-Divide by binary fission
-Size is similar to bacteria
-Contain plasmid DNA and ribosomes

Question 14

Prokaryotes vs Eukaryotes

Answer 14

-No nucleus (circular DNA in nucleoid) vs nucleus
-0.1-10 micrometers vs 10-100 micrometers
-70S vs 80S
-Peptidoglycan vs cellulose walls
-Corkscrew flagellum powered by H+ gradient vs complex flagella

Question 15

Describe the structure and function of the mitochondria

Answer 15

Structure:
-Bound by membranes: outer, inter membrane, inner membrane with cristae, and matrix.
-On the surface of the inner membrane and also embedded in it are proteins.
-Have their own DNA reminiscent of prokaryotic circular chromosomes (Endosymbiotic Theory).

Function:
-Cellular Respiration/ Factory of ATP

Question 16

Eukaryotic organelles with membranes

Answer 16

-Nucleus
-ER
-Golgi body
-Vesicles
-Mitochondria
-Chloroplast
-Lysosome: intracellular digestion
-Peroxisome: inactivating toxins
-Vacuole: storage

Question 17

Compare and contrast animal cells with plant cells.

Answer 17

Plants:
-cell wall composed primarily of cellulose
-chloroplast
-no flagella or cilia (except plant sperm cells)
-large central vacuole
-plasmodesmata
-store glucose as starch
-usually lack centrioles

Animals:
-no cell wall
-no chloroplasts
-can sometimes have flagella or cilia
-store glucose as glycogen
-centrosomes and lysosomes

Question 18

Describe the endomembrane system and list the components

Answer 18

-A system of intracellular membranes that are directly or indirectly connected
-One of the fundamental distinctions between eukaryotes and prokaryotes
-Divides cells into different compartments so that different functions can occur
-Nuclear envelope
-Endoplasmic reticulum
-Golgi apparatus
-Lysosomes
-Vesicles
-Plasma membrane

Question 19

Recognize the relationship between the endomembrane system and its functions

Answer 19

1. Vesicle containing proteins buds from rough ER, diffuses through cell, and buds to cis face of Golgi apparatus
2. The proteins are modified and packaged into vesicles for support.
3. The vesicle may travel to the plasma membrane, releasing its contents to the extracellular environment.

Question 20

Describe the cytoskeleton

Answer 20

The cytoskeleton is a system of protein fibers that criss-cross the cytoplasm, providing structural support, shape, and in some cases locomotion.

Question 21

Compare the roles of microfilaments, intermediate filaments, and microtubules.

Answer 21

Fibers that make up cytoskeleton:

-Microfilaments: also called actin filaments are thinnest parts (7 nm). Maintain/change cell shape, cell motility and division, muscle contractions. Actin subunit

-Intermediate filaments: fibers with diameters in middle range (8-12 nm), maintain cell shape, anchor nucleus and certain organelles, form nuclear lamina. Keratin subunit

-Microtubules: thickest of the three components

Question 22

Compare and contrast cilia and flagella

Answer 22

-flagella are responsible for movement, have long structures that extend beyond cell surface , and there can be multiple
-cilia: undulate or beat, shorter than flagella, used for movement and to move substances past surface in multicellular organisms

Question 23

List and describe examples of the ways animal and plant cells communicate with adjacent cells.

Answer 23

At tight junctions, membranes of neighboring cells are pressed together, preventing leakage of extracellular fluid.

Desmosomes (anchoring junctions:
A very strong spot weld
between cells. It is created by the
linkage of cadherins and intermediate filaments.

Gap junctions (communicating junctions):
A gap junction is a protein-lined pore that allows water and small molecules to pass between adjacent animal cells to provide cytoplasmic channels between adjacent cells

Plasmodesmata:
A plasmodesma is a channel between the cell walls of two plant cells allowing materials to pass between cytoplasms of cells
-Function similar to gap junctions in animal cells
-Water, nutrients, and signaling molecules can flow from cell to cell

Question 24

List the different classes of RNA and their functions.

Answer 24

mRNA- messenger RNA- specifies the amino acid sequence of a protein

tRNA- transfer RNA- adaptor molecule between amino and codon, tRNA carries amino to the ribosome during translation

rRNA- ribosomal RNA- has both structural and catalytic roles in ribosome

Question 25

Peroxisome

Answer 25

Peroxisomes oxidize amino acids and fatty acids, generating toxic hydrogen peroxide, which is then broken down by catalase. Catalase sometimes forms a crystal with the peroxisome.

Question 26

Central Vacuole

Answer 26

Plants:
Accumulates water and helps the cell elongate. Stores ions, organic compounds, water soluble pigments. Tonoplast is single membrane of vacuole.

Question 27

Centrioles

Answer 27

-They occur in pairs perpendicular to each other
-9 triplets of microtubule arrangements
-Nontubulin proteins hold them together

Question 28

Centrosome

Answer 28

-Region surrounding centrioles in most animal cells
-Micro-tubule organizing center

Question 29

Rough ER

Answer 29

Primary function the same in all cells
-Ribosomes attach to surface which deliver proteins into the ER membrane or lumen
-Starts synthesis of glycoproteins
-Distributes transport vesicles
-Is a membrane factory for the cell, makes phospholipids
-The ER membrane synthesizes nearly all of the major classes of lipids, including both phospholipids and cholesterol, required for the production of new cell membranes.

Question 30

Smooth ER

Answer 30

Primary function varies within cell types:
-Storage of calcium ions in muscle cells
-Detoxification of medicines and poisons
-Synthesis of carbohydrates, steroid hormones, and lipids

Question 31

Golgi apparatus

Answer 31

Structure:
-Flattened stacks of interconnected membranes called “cisternae”
-Cis face, receiving; trans face, delivery side

Functions:
-Vesicles transport molecules to destination
-Packaging and distribution of molecules synthesized in one location and used in another

Question 32

Lysosomes

Answer 32

-Membrane-bound vesicles
-Arise from Golgi apparatus
-Destroy cells or foreign matter cell has engulfed by phagocytosis
-Enzymes catalyze breakdown of macromolecules

Question 33

List the extracellular structures

Answer 33

-cell wall
-glycocalyx
-extracellular matrix

Question 34

Describe the cell wall

Answer 34

-layers of polysaccharide that provide structural support and rigidity to the cell
-plants: cellulose
-bacteria: various polysaccharides and peptidoglycan
-fungi: chitin
-most algae: various polysaccharides

Question 35

Describe the glycocalyx

Answer 35

Structure:
An outer filamentous coating of carbohydrate-
rich molecules on the surface of certain cells

Functions:
-Protection: cushions the plasma membrane and protects it from physical and chemical injury
-Cell Adhesion: Binds cells together so that the tissues don’t fall apart
-Defense against cancer: Changes in the glycocalyx of cancerous cells enable the immune system to recognize and destroy them
-Immunity
-Fertilization
-Transplant Compatibility: Forms the basis for compatibility of blood transfusions, tissue grafts, and organ transplants.

Question 36

ECM

Answer 36

-Secrete an elaborate mixture of
glycoproteins into the space around them
-Form a protective layer over the cell
surface
-Integrins link ECM to cell’s cytoskeleton

Question 37

Microtubules

Answer 37

Structure:
-Hollow tubes
-Consist of tubulin

Function:
-Maintenance of cell shape
-Cell motility
-Organelle movements
-Chromosome movements in cell division

Question 38

Organelles

Answer 38

Specialized parts of the cell that have unique jobs

Question 39

What structure makes ribosomes?

Answer 39

The nucleolus

Question 40

Where is the genome of a prokaryote located?

Answer 40

The nucleoid