STRUCTURES AND FUNCTIONS OF

EUKARYOTIC CELLS

STRUCTURES AND FUNCTIONS OF EUKARYOTIC CELLS

Recall: The kingdoms fungi, protista, plantae and animalia are all composed of eukaryotic cells

Similarities:

- Membrane bound nucleus with DNA

- Cell membrane composed of a phospholipid bilayer

- Cytoplasm filled interior (everything outside the nucleus but within the cell membrane – cytosol, organelles, molecules, ions)

ANIMAL CELL

PLANT CELL

NUCLEUSContains DNA

CHROMATIN: uncondensed DNA mixed with proteins

CHROMOSOME: condensed DNA molecule with an equal mass of protein

- Quantity varies between species (Ex: Humans have 46)

- Only visible during cell division

NUCLEUS

NUCLEUSNUCLEOPLASM: thick fluid filling the nucleus

NUCLEAR MATRIX: network of protein fibres providing internal structure and support

NUCLEUSNUCLEOLUS: non-membrane bound, denser region in the nucleus filled with RNA and proteins

NUCLEAR ENVELOPE: double membrane composed of a phospholipid bilayer which surrounds the nucleus

LUMEN: space between the bilayer

NUCLEAR PORE COMPLEXES: groups of proteins that form openings in the nuclear envelope; allow small particles and ions to travel freely

NUCLEUS

ENDOPLASMIC RETICULUM (ER)

Complex membrane-bound tubules and sacs attached to the nuclear envelope

SMOOTH ENDOPLASMIC RETICULUM (SER): endoplasmic reticulum without ribosomes

- Site of synthesis for lipids and lipid containing molecules

- Site specific functions (Ex: liver SER detoxifies drugs and alcohol, gonad SER produces testesterone and estrogen)

ROUGH ENDOPLASMIC RETICULUM (RER): ER surface studded with ribosomes

- Site of protein synthesis

ENDOPLASMIC RETICULUM (ER)

ENDOPLASMIC RETICULUM (ER)

RIBOSOMESStructure composed of RNA and proteins

Structure is different in eukaryotic and prokaryotic cells

Responsible for protein synthesis

a) Ribosomes attached to RER: proteins for cell membrane and cell export

b) Free floating ribosomes: proteins carrying out functions in the cytosol

RIBOSOMES

RIBOSOMES

GOLGI APPARATUSStack of curved membrane sacs

Packages, processes, sorts and distributes proteins, lipids and other substances within a cell

Produce lysosomes (animal cells only)

LYSOSOMESMembrane-enclosed sacs containing over 40 digestive enzymes (pH ~5)

- Catalyze hydrolysis reactions, break down macromolecules for parts to be reused in cell

- Break down old or no longer needed parts in cell

- Break down bacteria and other foreign particles

PEROXISOMESMembrane enclosed sacs containing enzymes that catalyze redox redox reactions

- Break down biological molecules and toxic molecules

- Found in large numbers in the liver to oxidize and break down alcohol

- Commonly produce hydrogen peroxide (H2O2) and so contain catalase to break it down into water and oxygen gas

- Can sometimes synthesize molecules (Ex: liver peroxisomes produce cholesterol and bile)

PEROXISOMES

VESICLES AND VACUOLES

VESICLE: membrane bound sacs used for the transport and storage of substances in the cell

- Formed by pinching off from cell membranes and organelle membranes

- Can fuse with cell membranes and organelle membranes to release their contents

• Animal Cell: Many small vesicles

• Plant cell: Single large central vesicle (Vacuole)

VESICLES AND VACUOLES

VACUOLEFound in plant cells

Stores water, ions, sugars, amino acids, and macromolecules

Contains enzymes that break down macromolecules and wastes

Determines turgor pressure in plants

ENDOMEMBRANE SYSTEM: PROTEIN MODIFICATION AND TRANSPORT

Consists of:

- Nuclear envelope

- Endoplasmic Reticulum

- Golgi Apparatus

- Vesicles

Function: synthesizing, product-processing and transportation section of cell; compartmentalizes cell

ENDOMEMBRANE SYSTEM: PROTEIN MODIFICATION AND TRANSPORT

ENDOMEMBRANE SYSTEM: PROTEIN MODIFICATION AND TRANSPORT

- Ribosomes on RER synthesizes polypeptides which are released into the lumen of RER

- Polypeptides travel through SER where they are stored and processed

- When ready for transport, pieces of SER pinch off into vesicles containing the protein

- Vesicles transport from SER to cis face of golgi apparatus

- Vesicle contents are released into the golgi apparatus where some proteins are stored and others are further modified

- Pieces of golgi apparatus pinch off from the trans face of the golgi apparatus and travel to the cell membrane or other destinations in the cell

ENDOMEMBRANE SYSTEM: PROTEIN MODIFICATION AND TRANSPORT

- Also used in transport of lipids and lipid containing molecules from SER

CHLOROPLASTSOrganelles containing the photosynthetic pigment chlorophyll, which absorbs light energy (plant cells only)

- Double membrane, own DNA

STROMA: thick liquid in the inner membrane

THYLAKOIDS: flattened disks containing chlorophyll

GRANUM: stack of thylakoids

MITOCHONDRIABreak down high-energy organic molecules to convert stored energy into usable energy

- Double membrane, own DNA

CRISTAE: folds of inner membrane

MATRIX: fluid filled space in inner membrane

CELL WALLRigid layer surrounding plant, fungi, and many types of protists

- Provides protection and support

- Composed of polysaccharides and/or glycoproteins

CYTOSKELETONInternal network of protein fibres that extend through the cytoplasm

- Provides structure and anchors cell membrane and organelles in place

- Act as tracks for vesicles and other organelles to move along

- For some cells, provides appendages that enable the cell to propel itself

CYTOSKELETON

CILIA AND FLAGELLAAppendages on the outside of of some eukaryotic cells

Composed of an internal shaft made of microtubules covered with an outer membrane that is a continuation of the cell membrane

Used for movement

FLAGELLA: One or two longer appendages

CILIA: many shorter appendages

CILIA AND FLAGELLA