Cell Structure and Function

1. 1–100µm

2. Why is there a limit to cell size?

a. Surface-to-volume ratio

b. Distance from surface to center

Cell Size

adult human

tallest trees

chicken egg

frog embryo

most eukaryotic cells

mitochondrionmost bacteria

virus

proteins

atoms

diameter of DNAdouble helix

Prokaryotic—no nucleus, circular DNA, ribosomes

Eukaryotic—larger, nucleus, linear chromosomes, membranous organelles

Cell types

Prokaryotic Cells

Have no membrane-bound organelles

Include true bacteria On earth 3.8 million years Found nearly everywhere

Spores in each breath; intestines

Naturally in soil, air, hot springs

ribosomes

cell wall

plasma membrane

food granule

prokaryoticflagellum

cytoplasm

nucleoid (DNA)

Eukaryotic Cells

Have numerous internal structures

Various types & formsPlants, animals, fungi, protists

Multicellular organisms

flagellum

cytoplasmrough endoplasmicreticulum

ribosome

microtubules

lysosome

mitochondrion

Golgi complex

plasmamembrane

intermediatefilaments

vesicle

smooth endoplasmicreticulum

free ribosomevesicle

nuclear porechromatin (DNA)

nucleolusnuclear envelope

nucleus

chloroplast

central vacuole

rough endoplasmicreticulum

ribosomes

microtubules(part of cytoskeleton)

cell wall

mitochondrion

Golgi complex

plasmamembrane

intermediatefilaments

smooth endoplasmicreticulum

free ribosome

vesicle

nuclear porechromatin

nucleolus

nuclear envelope

nucleus

Eukaryotic Cell Structure

Cytoplasm is the clear, gelatinous fluid inside of a cell

Eukaryotic cell structure

Nucleus is control center of the cell

1. Membrane bound (nuclear envelope)

2. Contains nucleoli; synthesizes ribosomal RNA

3. DNA in chromosomes (DNA and proteins)

nuclear pores

chromatin

nucleolus

nuclear envelope

nuclear pores

nucleus

chromosome

chromatin

Eukaryotic cell structure

Organelles

Endoplasmic reticulum consists of folded membranes attached to the nucleus

Rough ER is site of protein synthesis and protein secretion

0.5 micrometers

smooth endoplasmic reticulum

vesicles

ribosomes

rough endoplasmic reticulum

0.5 micrometers

Eukaryotic Cell Structure

Organelles (cont.)

Ribosomes assemble amino acid into polypeptide chains

• a. Associated with the ER

• b. Composed of RNA and proteins

0.5 micrometers

ribosomes

rough endoplasmic reticulum

0.5 micrometerssmooth endoplasmic reticulum

vesicles

Eukaryotic Cell StructureOrganelles (cont.)

Golgi apparatus are membranous sacs associated with ER

• a. Processing and transport of proteins, lipids

• b. Synthesis and transport of polysaccharides

Golgi complex

vesiclesfrom ER

vesiclesleavingGolgi complex

Eukaryotic Cell Structure

Vacuoles: membrane-bound compartments that are temporary storage of materials

Animal cells do not usually contain vacuoles, if they do they are very small

Plant cells usually use them for water storage

Eukaryotic cell structure

Organelles (cont.)

Lysosomes are Golgi-derived vesicles containing digestive enzymes

Digest excess or worn out organelles, food particles, and engulfed viruses or bacteria

Golgi complex

vesiclesfrom ER

vesiclesleavingGolgi complex

Eukaryotic Cells: Organelles Energy sources for cell activities

Mitochondria provide energy for cellular functions (respiration)

• a. Membrane bound, numerous

• b. Matrix/cristae

• c. Have their own DNA and ribosomes; self-replicate

5 micrometers

Eukaryotic Cells: Organelles Energy sources for cell activities

• Chloroplasts—function in photosynthesis

1) Green—contain chlorophyll pigment

2) Stroma/grana (thylakoid stacks)

3) Have their own DNA and ribosomes; self-replicate

4) Up to 100 per cell

Eukaryotic Cells: Organelles

CytoskeletonInternal infrastructure

Surface structures

extensions of the plasma membrane aid in movement of simple organisms

tubulinsubunit

actinsubunits

subunit

Cytoskeleton

Microtubules-thin hollow cylinders made of protein

Microfilaments- smaller, solid protein fibers

They work together to maintain the shape of the cell

Centrioles

Organelles found in the cells of animals and most protists

Occur in pairs and are made up of microtubules

Play an important role in cell division

Cilia and Flagella

Cilia are short, numerous projections that look like hairs

Flagella are longer projections that move with a whip-like motion

Both are used for locomotion or feeding

Prokaryotes & Eukaryotes

Similarities & differences

Both surrounded by plasma membrane, but very different

Prokaryotes – Archaebacteria and Eubacteria

Eukaryotes – everything else

Plant & Animal Cells

Similarities

Both constructed from eukaryotic cells

Both contain similar organelles

Both surrounded by cell membrane

Plant & Animal Cells

Differences

Plants have• Cell wall – provides strength & rigidity• Have chloroplasts, photosynthetic

Animals have• Other organelle not found in plants

(lysosomes formed from Golgi)• Centrioles, important in cell division

Brief Look at Viruses

Viruses are acellular

Not considered to be living

Cause serious diseases in most organisms