Inside the Cell:Part 1

Dr. Corl

BIOL 105

September 9, 2013

Inside the Cell:

Introduction

• The Cell Theory:– All organisms are composed of cells– All cells are derived from preexisting cells

• All cells have:– Nucleic acids (to store genetic information)– Proteins (e.g. enzymes which speed up reactions)– Carbohydrates (provide chemical energy)– Plasma membrane (aka cell membrane)

Prokaryotes vs. Eukaryotes

• Two broad groupings of life, based on cell structure:

– Prokaryotes (e.g. bacteria)• Lack a membrane-bound nucleus.

– Eukaryotes (e.g. plants and animals)• Have a membrane-bound nucleus (nuclear

envelope)

Prokaryotic Cells

• Plasma membrane:– Encased by a cell wall:

• Helps protect the cell inside.

– Surrounds the cytoplasm:• Interior contents of the cell.

• Flagellum:– Spins to help cell move.

• Fimbriae:– Numerous needlelike

projections.– Help cell to adhere to other

cells or surfaces.

Prokaryotic DNA

• Most genes are contained within a single, circular, DNA-containing chromosome.

• NO nuclear membrane.• Prokaryotes may also have a few other genes contained within small,

circular plasmids.

Prokaryotic Ribosomes

• Ribosomes:– Made up of RNA and protein molecules.– Important for manufacturing proteins.

Differences Between Prokaryotes and Eukaryotes

• Eukaryotic cells:– House DNA in a membrane-bound nucleus.– Are usually much larger than prokaryotic cells.– Contain extensive internal membranes.– Have a diverse and dynamic cytoskeleton.

Membranearound nucleus

No nucleus

Compartmentalization into Organelles

• Due to large size of eukaryotic cells:

– Volume is compartmentalized into many smaller membrane-bound organelles.

– Different organelles perform different functions. For example:

• Chloroplasts: conduct photosynthesis• Lysosomes: contain digestive enzymes

Typical Animal Cell

Typical Plant Cell

Nucleus

• Contains a cell’s genetic information:– Stored in the DNA sequences of chromosomes.

Nucleus

• Bounded by double membrane: nuclear envelope.• Contains a nucleolus: where ribosomal RNA is synthesized.

• Composed of proteins and RNA.• Found scattered in the cytosol (the fluid portion of the cytoplasm).• Involved in protein synthesis.

Ribosomes

Rough Endoplasmic

Reticulum (ER)

• Network of membrane-bound sacs and tubules, lined with ribosomes.

• Many proteins are synthesized here.

Golgi Apparatus

• Consists of flattened membranous sacs (cisternae).• Receives products from rough ER and processes them.• Sends finished products to cell surface (and other locations).

Smooth Endoplasmic

Reticulum

• Lacks ribosomes.• Site of lipid biosynthesis. May store Ca2+ ions.

Endomembrane System

• Primary center for protein and lipid synthesis in the cell.

• Consists of:– Rough endoplasmic reticulum.– Smooth endoplasmic reticulum.– Golgi apparatus.– Lysosomes.

Lysosomes

• Have a relatively acidic lumen (interior: pH = 5).• Contain many digestive enzymes (acid hydrolases):

– Involved in digesting various molecules into monomers.

Delivering Materialto Lysosomes

Receptor-mediated

Endocytosis

EndocytosisEndocytosis:

– Any pinching off of the plasma membrane that results in uptake of material from outside the cell.

– 3 types of endocytosis:

• 1.) Phagocytosis• 2.) Pinocytosis

– Cell “drinks” in small droplets of extracellular fluid when cell membrane folds inwards and pinches off.

• 3.) Receptor-mediated

endocytosis

Vacuoles

• Plant and fungi have large vacuoles.

• Store water, ions, and nutrients.

Peroxisomes

• Perform oxidative reactions:– Reactions that remove

electrons from molecules.

• Peroxisomal enzymes:– Help metabolize fatty

acids into smaller molecules.

– Help detoxify many toxins, including alcohol.

– Include catalase, which breaks down H2O2.

Mitochondria

• Have two membranes, their own DNA and their own ribosomes.

• Involved in producing ATP, the cell’s energy currency.

Chloroplasts

• Found in plant and algal cells.• Have two membranes and their own DNA.• Involved in photosynthesis:

– Converting light energy into chemical energy.

Chloroplasts

• Interior dominated by thylakoid membranes:– Stacks of thylakoids: grana.– Interior of thylakoids: lumen.

• Stroma: fluid surrounding thylakoids.

Cytoskeleton and Cell Wall

• Cytoskeleton:– Fibers which gives the cell shape and structural stability.

• Cell Wall:– Protects the cell. – Found in fungi, algae, and plants.

Cell Structure and Function

• A cell’s structure correlates with its function.– Testis cell:

• Lipid exporting cell - has lots of smooth ER.

– Plant leaf cell:• Sugar manufacturing cell - has lots of chloroplasts.

Summary Table

Summary Table

Typical Animal Cell

Typical Plant Cell

Review Questions

• How do prokaryotic cells differ from eukaryotic cells?

• Describe the components of the endomembrane system.

• What cellular components are found in the nucleus?

• Contrast the function of the mitochondrion versus the chloroplast.