Cell Structure and Function

Chapter 3

The Cell--Considerations• Basic unit of life

• Protection and support

• Movement

• Communication

• Metabolism and energy release

• Inheritance

Cell TheoryAll living things are made up of

cell(s)

Cells are smallest living unit of structure and function for all organisms

All cells arise from preexisting cells

(No spontaneous generation)

Why Are Cell So Small?

Sizes of living things

Prokaryotes vs Eukaryotes

• Prokaryotes– “Before nucleus”– DNA in nucleoid region– Ribosomes– Cell membrane– No membrane–bound

organelles

• Eukaryotes– “True nucleus”– DNA in double

membrane bound nucleus

– Ribosomes– Cell membrane– Membrane –bound organelles

Typical Bacterium---A Prokaryote

Typical Animal Cell-A Eukaryote

Plasma Membrane

Animal cell anatomy

Plant cell anatomy

Nucleus--The Brains of the Cell

Nucleus

• DNA dispersed throughout• Consists of :

– Nuclear envelope: Separates nucleus from cytoplasm and regulates movement of materials in and out

– Chromatin: Condenses to form chromosomes during cell division

– Nucleolus: Assembly site of large and small ribosomal units

Ribosomes

• Sites of protein synthesis

• Composed of a large and small subunit

• Types– Free– Attached to

endoplasmic reticulum

Composition of eukaryotic and

prokaryotic ribosomes

Cryoelectron microscopy–based image of the E. coli ribosome at ~25 Å resolution.

Mol. Biol. Gene, Fig. 14-21

The Endomembrane System

• Nuclear envelope

• Endoplasmic reticulum

• Golgi apparatus

• Vesicles

Endoplasmic Reticulum• Types

– Rough• Attached ribosomes• Proteins produced

and modified– Smooth

• No attached ribosomes

• Manufacture lipids• Cisternae or Lumen:

Interior spaces isolated from rest of cytoplasm

Golgi Apparatus—Traffic Cop

• Modification, packaging, distribution of proteins and lipids for secretion or internal use

• Flattened membrane sacs stacked on each other

Function of Golgi Apparatus

Action of Lysosomes

Peroxisomes and Proteasomes

• Peroxisomes– Smaller than lysosomes– Contain enzymes to break down fatty and

amino acids– Hydrogen peroxide is a by-product of

breakdown

• Proteasomes– Consist of large protein complexes– Include several enzymes that break down

and recycle proteins in cell

Energy Management Organelles

• Mitochondria

–Aerobic Respiration

• Chloroplasts

–Photosynthesis

Circle of Life

Carbon compounds, O2

CO2, H2O

Respiration

Photosynthesis

Energy

Energy

Mitochondria

Chloroplasts

Complex>>Simple

Mitochondria—Powerhouse of the Cell• In all eukaryotes• Major site of ATP

synthesis• Membranes

– Outer– Cristae: Infoldings of

inner membrane

• Matrix: Substance located in space formed by inner membrane

Chloroplast

Animal cell anatomy

Plant cell anatomy

The Cytoskeleton• Function:

– Maintenance of cells shape– Movement within cytoplasm– Cell movement – Intracellular communication?

• Three components – Actin filaments– Microtubules– Intermediate filaments

FUNCTION:

CYTOSKELETON= complex network of filamentous proteins extending throughout the cytoplasm

Three types of filaments: Microtubules Microfilaments Intermediate Filaments

Cell shape

Motility:crawling,chemokinesis chemotaxisendo- and exo-cytosis)

Anchoring of organelles and cellular structures

Organelle movement

Cell polarity

Tensile strength

Chromosome movement

helical structure, diameter ~ 7 nm EX. intestinal microvilli

ACTIN FILAMENTS

MICROFILAMENTSACTIN STRUCTURES IN CELLS:

MICROVILLI STRESS FIBRESFOCAL ADHESIONS

LAMELLIPODIAFILOPODIA(or MICROSPIKES

CONTRACTILERING(cell division)

hollow cyllinders, diameter ~ 25 nm, emanating from the MTOC

Microtubule structure

Made of and β Tubulin

rope-like fibres, diameter ~ 10 nm, nuclear, cytoplasmic, connecting cell-cell junctions

Structure of intermediate filaments

micro-tubule

s

micro-filaments

intermediate

filaments

Cytoskeleton Elements

Centrioles

Centrioles• In specialized zone

near nucleus: Centrosome

• Each unit consists of microtubules

• Before cell division, centrioles divide, move to ends of cell and become spindle fibers

Cilia and flagella

• Cilia (small and numerous) and flagella (large and single)

–9 + 2 pattern of microtubules

– Iinvolved in cell movement.

–Each has a basal body at its base.

• Plant cells lack centrioles

Structure of a flagellum or cilium

Prokaryotes vs Eukaryotes

• Prokaryotes– “Before nucleus”– DNA in nucleoid region– Ribosomes– Cell membrane– No membrane–bound

organelles

• Eukaryotes– “True nucleus”– DNA in double

membrane bound nucleus

– Ribosomes– Cell membrane– Membrane –bound organelles

Evolution of the eukaryotic cell- Endosymbiotic Hypothesis

SUMMARY• Cell Theory• Physics of Cell Size• Eukaryotes

– Nucleus– Membrane Bound Organelles

• ER• Golgi• Vesicles, ex. Lysosomes

– Energy Management Organelles– Cytoskeleton– Prokaryotes– Endosymbiosis