CELLS

BY: MS. REIS

Prokaryotic Cells

• Does not have a “true” nucleus

• Lacks membrane bound organelles

• Usually unicellular• Bacteria are

prokaryotic

•

Eukaryotic Cells

• Includes animals, plants, fungi and protists• DNA contained in membrane-bound

nucleus• Contains cell membrane comprised of a

phospholipid bilayer (double layer)• Cytoplasm is the jelly-like interior

consisting of everything outside the nucleus but within the cell membrane.

• Cytosol is the fluid

Eukaryotic Cells

Cell Membrane• Phospholipid

bilayer• Selectively

permeable – allows some materials in while keeping other materials out of the cell

Nucleus• organelle bounded by a double –

layered porous membrane called the nuclear membrane/envelope.

• control center of the cell • Contains the cell’s genetic

material or DNA (deoxyribonucleic acid)

• Nucleolus - darker area within the nucleus that manufactures rRNA (ribosomal ribonucleic acid) present in ribosomes

Nucleus• The nuclear envelope

contains many openings called pores.

• Small particles such as water and ions travel freely through the openings, but the passage of macromolecules such as RNA is controlled by the pores

• The nuclear envelope is connected to the endoplasmic reticulum

Cytoplasmic Organelles

Endoplasmic Reticulum (ER) – small tubules or canals branching from the nucleus that allow the transportation of materials within the cell

Smooth ER – ribosomes absent, synthesize lipids

Rough ER – ribosomes present, synthesize proteins that are part of membranes or intended to be exported from the cell

Ribosomes – synthesize proteins that function in the cytosol

The Endomembrane System

• Consists of the nuclear envelope, the endoplasmic reticulum, the Golgi apparatus, and vesicles

• These organelles are connected and work together to carry out many processes in the cell

The endomembrane system modifies and transports proteins

Functions of the Endomembrane System

• Ribosomes on the surface of the ER produce polypeptides and released into the lumen

• Manufactured polypeptides travel to smooth ER, where they are stored and processed. When proteins are ready for transport, smooth ER pinches off to form vesicles containing the proteins.

Endomembrane System• Vesicles from the smooth ER travel across the cell to

the cis face of the Golgi Apparatus. The vesicles merge with the membrane of the Golgi Apparatus and release their contents.

• Golgi Complex- Flattened stacks of membrane that receive, modify and transport proteins from the ER.

•

Endomembrane System

• When the modified proteins are ready for transport, pieces of the Golgi pinch off from the trans face to form vesicles. The vesicles transport the proteins to the cell membrane or other destinations.

Lysosomes Peroxisomes• Membrane bound

sacs performing a digestive function

• Contains enzymes to digest food, wastes, invading bacteria and breaks down old organelles

• Present in animal cells only

• Golgi apparatus produces lysosomes

• Tay – Sachs disease

• Membrane bound sacs performing a digestive function

• Enzymes in peroxisomes are oxidases that catalyze redox reactions

• Liver contains many peroxisomes to break down alcohol

• Form by budding off from ER

• Present in animal cells only

Vacuoles• Functions include

storage and support through turgor pressure (the pressure exerted by water on cell membrane and cell wall).

• fluid-filled space that stores water, food and wastes.

• Very large organelle in plant cells, but small in animal cells

Plastids: Chloroplasts

• Make food for the cell through photosynthesis• Chloroplasts contain chlorophyll to trap light

energy needed for photosynthesis• Present in plant cells but not in animal cells• Chromoplasts – type of plastid that stores

orange and yellow pigments found in fruits and flowers

• Amyloplasts – type of plastid that stores starch in potatoes.

Chloroplast Structure• Stroma – fluid of the

chloroplast containing enzymes

• Thylakoids – disks containing chlorophyll

• Grana (sng: granum)-

stack of thylakoids

Mitochondria• Provides stored energy

(ATP) for the cell in a process called cellular respiration

• Cristae – inner folds provide large surface area containing enzymes to speed up cellular respiration.

• Matrix – inner liquid solution

• Intermembrane Space – space between outer membrane and cristae

Endosymbiotic Theory• Both mitochondria and chloroplasts contain their

own DNA (mt DNA is circular like that of bacteria), reproduce on their own and are about the same size of a bacteria.

• Dr. Lynn Margulis in 1960 proposed that mitochondria and chloroplasts were once separate organisms: bacterial cells and algal cells respectively that invaded other eukaryotic cells approximately 1.4 billion years ago

Cell Wall

• Composed mainly of cellulose in plant cells

• Provides structure and support for the cell

• Present in plant cells, fungus and bacteria but not in animal cells.

• The antibiotic penicillin prevents the formation of bacterial cell walls.

Cytoskeleton

• 3 types of protein fibers: microfilaments, intermediate filaments,microtubules

• Extend throughout the cytosol to maintain cell shape, anchor organelles and facilitate movement of organelles

Plant Cell vs Animal Cells

Plant Cells Animal Cells

Cell wall and Chloroplasts

present absent

Vacuole large small

Peroxisomes and

Lysosomes

absent present

Shape boxed spherical

Red Blood Cells

• Red blood cells are formed in bone marrow. These oxygen carrying cells expel their nuclei to make more room for oxygen in the cell.

• DNA testing in blood uses white blood cells instead.

Cilia and Flagella

• Are appendages that develop on the outside of eukaryotic cells

• Flagellum – whiplike tail used for cell movement

• Cilia – tiny hairs also used for locomotion

• In humans cilia allow particles to move out of the respiratory tract

• In paramecia cilia propel food toward a feeding groove