Answered Review QuestionsCell Structure and Function

Cell Structure

Location-Structure Function Prokaryote/Eukaryote

Cell membrane (Plasma membrane)

Forms outer boundary of cell;

Forms membrane-bound organelles

Semi-permeable (restricts the access of certain compounds and ions)

Aids in maintaining the complex internal organization of a cell

Both

Cytoplasm Everything between the nuclear envelope (nucleoid region in prokaryotes) and the cell boundary

Site of most chemical reactions of life

Both

Cytosol The semi-fluid portion of the cytoplasm

Both

Nucleus 10% of the volume of the cell Mission control—manages protein synthesis

Eukaryotes only

Nucleolus Small dense spheres within the nucleus (often 2-3 visible)—tightly coiled regions of the DNA

Genes for ribosomal RNA (building block of ribosomes)

Eukaryotes only

Nuclear envelope

Porous double-membrane organelle;

Forms outer boundary of nucleus

Protects the DNA

mRNA exits the nucleus through pores after transcription

Eukaryotes only

Bound ribosomes

Small dense granules (each has a large and a small subunit) made of proteins and rRNA;

Attached to endoplasmic reticulum;

Can become free;

Part of the endomembrane system

Site of protein synthesis

Ribosomes build proteins

Eukaryotes only

Free ribosomes

Small dense granules (each has a large and a small subunit) made of proteins and rRNA;

Suspended in cytosol;

Can become bound

Site of protein synthesis

Ribosomes build proteins

Both

Rough endoplasmic reticulum

Network of membranous tubes dotted with bound ribosomes;

Loosely surrounds the nucleus;

Part of the endomembrane system

Modify proteins

Many proteins are modified here by cleaving the polypeptide, forming quaternary structures, removing amino acids or adding non-protein substances (e.g. enzymes often require a metallic ion to work)

Eukaryotes only

Smooth endoplasmic reticulum

Network of membranous tubes;

Loosely surrounds the nucleus;

Part of the endomembrane system

Makes carbohydrates and lipids

(e.g. the SER of liver cells convert glucose to glycogen, and make triglycerides and cholesterol)

Eukaryotes only

Transport vesicle

Membrane-bound bubble;

Buds off both RER and SER;

Part of endomembrane system

Moves modified proteins, lipids, and carbohydrates to cis face of Golgi apparatus

Eukaryotes only

Golgi apparatus Network of membranous tubes;

Located closer to cell boundary than ER;

Cis face toward nucleus;

Trans face toward cell membrane;

Part of the endomembrane system

Receives compounds from ER;

Attaches a chemical “address label” for compounds destined for export

Eukaryotes only

Secretory vesicle

Membrane-bound bubble;

Buds off trans face of Golgi apparatus;

Part of endomembrane system

Moves finished compounds to cell membrane for export

Eukaryotes only

Lysosome Membrane-bound bubble containing hydrolytic enzymes;

Buds off Golgi apparatus

Cell’s stomach;

Merges with food vacuole and digests organic compounds;

Autophagy (recycles old and damaged organelles and cytosol);

Apoptosis (programmed cell death/self-destruction)

Eukaryotes only

Food vacuole Membrane-bound bubble;

Buds off cell membrane

Transports food particles and captured microbes from outside the cell into cytoplasm;

Fuses with lysosome

N/A

Mitochondrion Double membrane bound organelle;

Inner membrane called cristae;

Semi-fluid interior called matrix;

Has own DNA and protein-making machinery

Descendent of free-living prokaryote

Aerobic cellular respiration;

Harvests chemical energy from organic monomers and stores the energy in ATP

Eukaryotes only

Chloroplast Double membrane bound organelle;

Inner membrane discs called thylakoids;

semi-fluid space surrounding thylakoids called stroma;

Has own DNA and protein-making machinery

Descendent of free-living prokaryote

Photosynthesis;

Harnesses light energy and uses it to build sugar

Eukaryotes only

(Plants and Photosynthesizing Protists)

Cytoskeleton All through cytoplasm

Three filament types (Listed below)

Gives shape to cell; Supports organelles;

Aids in motion and cell division;

Moves material (organelles) through cytoplasm

Actin Filaments One kind of cytoskeletal element;

Most often located just below cell membrane;

Twisting strand of globular actin subunits

Movement (e.g. Amoeba pseudopods, cytoplasmic streaming, formation of cleavage furrow, microvilli extension and retraction)

Eukaryotes only

Microtubules One kind of cytoskeletal element;

Spread through out cytoplasm;

Small hollow tube built of tubulin dimers

Internal monorail system for moving organelles through cytoplasm;

components of centrosome, centrioles, cilia, and flagella;

Microtubules are the spindle fibers that move the chromosomes in cell division

Eukaryotes only

Intermediate filaments

One kind of cytoskeletal element;

Spread through out cytoplasm;

Anchored to cell membrane and organelles

Scaffolding that supports organelles;

Gives shape to cells

Eukaryotes only

Centrosome (Microtubule Organizing Center [MTOC])

Within cytoplasm;

In animal cells the location is covered by a pair of centrioles

Region of the cytoplasm that makes spindle fibers for cell division

Eukaryotes

Centriole Small pair of hollow tubes;

Built of microtubules

Organized into a 9+0 arrangement

Covers centrosome in animal cells

Associated with cell division but not necessary

Eukaryotes (Animal cells)

Cilia Small oar-like structure projecting outside the cell membrane;

Built of microtubules (9+2 arrangement);

Basal body has 9+0 arrangement like centriole

Synchronized rhythmic rowing;

Movement for single-celled microbes;

Ciliary escalator in trachea

Eukaryotes

Flagella Long whip-like tail projecting outside the cell membrane;

Built of microtubules (9+2 arrangement);

Basal body has 9+0 arrangement like centriole

Wiggles back and forth moving cell through liquid;

Sperm cells have a flagellum

Both (prokaryotic flagella are different in

structure and motion [rotary])

Central Vacuole

Large membranous sac in plant cells;

Takes up most of the space in cytoplasm

Maintains structural integrity of plant cells (turgidity);

Water storage;

Alkaloid storage;

Pigment storage

Eukaryotes (Plants only)

Perioxisome Small membrane bound organelle in aerobic eukaryotes

Catalase enzymes in organelle convert hydrogen peroxide (slightly toxic intermediate metabolite of superoxide free radical breakdown) to water and oxygen gas

Eukaryotes

PLASMA MEMBRANE

NUCLEUS, NUCLEAR ENVELOPE, NUCLEAR PORES

GENERALIZED ANIMAL CELL

GENERALIZED PLANT CELL

BOUND AND FREE RIBOSOMES

RER AND SER

GOLGI APPARATUS

LYSOSOME

MITOCHONDRION

CHLOROPLAST

PEROXISOME

CENTRIOLES

FLAGELLA AND CILIA

MICROTUBULES

ACTIN FILAMENT

INTERMEDIATE FILAMENT

Trace the path of the production of a protein from the DNA in the nucleus to its secretion outside the cell. (endomembrane system). Explain the function of each member.

Proteins are synthesized by the bound ribosome. The resulting protein is modified (glycoprotein is attached, plus any other modifications) by the rough endoplasmic reticulum. A small section of the RER containing the protein pinches off the end enclosing the protein inside a transport vesicle. The transport vesicle moves to the Golgi apparatus where it fuses with the cis face of the Golgi apparatus. The protein receives a chemical address label (glycoprotein is modified) as it is moved through the layers of membranous sacs of the Golgi apparatus. On the trans face of the Golgi apparatus the finished protein is enclosed inside a secretory vesicle that moves to the cell membrane and dumps the protein out of the cell.

Secretory vesicle

Lipids or carbohydrates are synthesized by the smooth endoplasmic reticulum. A small section of the SER containing the compound pinches off the end enclosing the protein inside a transport vesicle. The transport vesicle moves to the Golgi apparatus where it fuses with the cis face of the Golgi apparatus. The compound receives a chemical address label (glycoprotein is modified) as it is moved through the layers of membranous sacs of the Golgi apparatus. On the trans face of the Golgi apparatus the finished compound is enclosed inside a secretory vesicle that moves to the cell membrane and dumps the compound out of the cell.

Explain the endosymbiosis theory.Mitochondria and chloroplasts have many characteristics that make them look like prokaryotic cells (see table below). Lynn Margulis hypothesized that these two energy-producing organelles were once free-living prokaryotes with a special talent that were engulfed but not digested by a larger prokaryote. A mutalistic relationship developed. The smaller aerobic cellular respiring bacterium was protected and in return the larger symbiont was supplied with energy. In plants and photosynthesizing protists, symbiotic cyanobacteria were added to the mix making the larger symbionts autotrophic.

Contrast plant and animal cells. See comparison below.