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Cells: The Living Units

Describe two important functions of the Golgi apparatus

To modify, sort and package proteins

Why can we say that a cell without a nucleus will ultimately die?

Can't make proteins

Can't replace enzymes or other cell structures which are continuously recycled

Can't replicate

Are Brownian motion, diffusion, and osmosis seen only in living tissue?


Passive processes that do not require energy

Occur in the absence of any cellular processes.

What forces maintain a steady state "resting" membrane potential?

Both diffusion and active transport mechanisms operate within the cell membrane to maintain a resting membrane potential

Briefly describe the glycocalyx

Sticky, carbohydrate-rich area on cell surface.

Binds cells together

Provides a highly specific biological marker by which cells can recognize each other

Explain the term genetic code. What does it code for? What are the letters of the code?

The genetic code is the information encoded in the nucleotide base sequence of DNA.

A sequence of three bases, called a triplet, specifies amino acid in a protein.

The letters of the code are the four nucleotide bases of DNA designated as A, T, C, and G.

Why are the free radicals so dangerous to cells and how are they dealt with by the body?

Highly reactive chemicals

Cause havoc in any cellular environment by reacting with things they should not.

Cells with peroxisomes have enzymes specific to reducing free radicals into less reactive chemicals.

In all living cells hydrostatic and osmotic pressures exist. Define these pressures and explains how they are used in the concept of tonicity of the cell?

Hydrostatic pressure: pressure of water exerted on the cell membrane

Osmotic pressure: created by different concentrations of molecules in a solution separated by the cell membrane

Pressures are exerted on the membrane

Used by the cell to change the shape of the cell

Regulate substances entering and exiting the cell

Brings about polarity of the cell

What is the common route of entry for flu viruses into a cell?

Receptor-mediated exocytosis.

Attaches to the receptors or to the substances

Receptors accept to "hitch a ride" into the cell

Other than the nucleus, which organelle has its own DNA?


How are the products of free ribosomes different from membrane-bound ribosomes?

Free ribosomes: Make soluble proteins that function in the cytosol.

Membrane-bound ribosomes: Produce proteins that are to be used on the cell membrane or exported from the cell

How are peroxisomes different from lysosomes?

Oxidases that use oxygen to detoxify harmful substances.
Neutralize free radicals.
Divide by budding.

Hydrolytic enzymes that destroy anything they come in contact with.
Manufactured by the Golgi apparatus.

Briefly name the subphases of interphase and tell what they do

G1 - growth phase. The cell is metabolically active and the centriole begins to divide at the end of this phase

S - DNA replicates itself. New histones are made and assembled into chromatin

G2 - Enzymes and proteins are synthesized and centriole replication is completed. This is the final phase of interphase.

List the steps in the process of transcription


What are nucleolar organizer regions?

Nuclear regions containing the DNA that issues genetic instructions for synthesizing ribosomal RNA

How is the resting potential formed? How is it maintained?

It is formed by diffusion of ions resulting in ionic imbalances that polarize the membrane.

It is maintained by active transport processes.

List possible causes of aging

Chemical insults and free radical formation (wear & tear)

Diminished energy production by free radical-damaged mitochondria

Progressive disorders in the immune system

Genetic programming

What factors contribute to the fragility of the lysosome and subsequent cell autolysis?

Cell injury

Cell oxygen deprivation

Excessive amounts of vitamin A in the cell

Why can we say that cells are protein factories?

Most of the metabolic machinery of the cell is involved in protein synthesis

Structural proteins constitute most of the cell dry material

Functional proteins direct all cellular activities

What are cell exons and introns?

Exons are amino acid-specifying informational sequences in genes
Introns are noncoding gene segments that provide a resevoir of ready-to-use DNA segments for genome evolution and a source of a large variety of RNA molecules

What are lipid rafts? What are their function?

They are assemblies of saturated phospholipids associated with sphingolipids and cholesterol.

They are concentrating platforms for molecules needed for cell signaling

Produces ATP aerobically


Site of enzymatic breakdown of phagocytized material


Packages proteins for insertion in the cell membrane or for exocytosis

Golgi apparatus

Site of synthesis of lipid and steroid molecules

Smooth ER

Forms the mitotic spindle


Replicate for cell division


Source of cell autolysis


Nonpolar region of phospholipid

Polar tail


Attached to the end of outside of polar head

Polar region of phospholipid

Polar head

Peripheral protein

Outside of polar head

Integral protein

Embedded within the bilayer

Identification "tags" for the cell


Hydrophilic portion

Polar head

Forms part of the protein synthesis site in the cytoplasm

Ribosomal RNA

Act as "interpreter" molecules that recognize specific amino acids and nucleotide base sequences

Transfer RNA

Attaches the correct amino acid to its transfer RNA

Synthetase enzymes

Provides the energy needed for synthesis reactions


Found in the cytoplasm, this structure specifies the exact sequence of amino acids of the protein to be made

Messenger RNA

May be attached to the ER or scattered in the cytoplasm

Ribosomal RNA

Chromosomes decoil to form chromatin


Chromosomal centromeres split and chromosomes migrate to opposite ends of the cell


Nuclear membrane and nucleolus disintegrate

Late prophase

Chromosomes align on the spindle equator


Centrioles move to opposite ends of cell

Early prophase

Plays a role in the synthesis of steroid-based hormones and proteins

Endoplasmic Reticulum

The actual site of protein synthesis


Hollow cytoskeletal elements that act as organizers for the cytoskeleton


Dense spherical bodies in the nucleus that are the synthesis sites for ribosomal RNA


Houses DNA and RNA


Help prevent molecules from passing through the extracellular space between adjacent cells

Tight junctions

Type of anchoring junction


Communicating junction


Present in electrically excitable tissues


Abundant in tissues subjected to great mechanical stress


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