What is a cell?

• Each cell has a plasma membrane, cytoplasm, and a nucleus (in eukaryotic cells) or a nucleoid (in prokaryotic cells)

• Surface-to-volume ratio limits cell size

What is cell theory? • Three key points of the cell theory:

– organisms consist of one or more cells– smallest unit that retains the capacity

for life– arises from the growth and division of

another cell

How do we see cell?

• Different microscopes use light or electrons to reveal details of cell shapes or structures

What is the structure of membrane?

• Each cell membrane is a boundary (lipid bilayer)– controls flow of

substances across it

cytoplasm membraneprotein

extracellularenvironment

one layerof lipids

Fluid mosaic modelMembrane is composed of phospholipids, sterols, proteins, and other componentsPhospholipids drift within the bilayer

one layerof lipids

What are membrane proteins?

• Many proteins are embedded in or attached to cell membrane surfaces– Receptors,

transporters, communication proteins, and adhesion proteins

• Plasma (outer) membrane also incorporates recognition proteins

What are prokaryotic cells?• Bacteria and

archaeans– The simplest cells– The groups with

greatest metabolic diversity

• Biofilms – Shared living

arrangements of prokaryotes

• Cell wall– Surrounds plasma

membrane• Flagella

– Used for motion• Pili

– Protein filaments used for attachment

– “Sex” pilus transfers genetic material

What are eukaryotic cells?

• Start with a nucleus and other organelles– Carry out

specialized functions inside a cell

Let’s explore the nucleus• Nucleus separates DNA

from cytoplasm– Chromatin (all

chromosomal DNA with proteins)

– Chromosomes (condensed)

• Nucleolus assembles ribosome subunits

• Nuclear envelope encloses nucleoplasm– Pores, receptors,

transport proteins

What is the endomembrane system ?

• Endoplasmic reticulum (ER) – An extension of the nuclear envelope– RER modifies new polypeptide chains– SER makes lipids; other metabolic

functions• Golgi bodies

– Further modify polypeptides– Assemble lipids

What else does it do?• Vesicles

– Endocytic and exocytic: Transport or store polypeptides and lipids

– Peroxisomes: Digest fatty acids and amino acids; break down toxins and metabolic by-products

– Lysosomes: Intracellular digestion (animals)– Central vacuole: Storage; fluid pressure (plants)

Other organelles!

• Mitochondria – Break down organic

compounds by aerobic respiration (oxygen-requiring)

– Produce ATP• Chloroplasts

– Produce sugars by photosynthesis

Cell wall only in plant cells!

• prokaryotes, protists, fungi, all plant cells have cell wall around their plasma membrane– Protects, supports,

maintains cell shape

– Primary and secondary cell walls

• Plasmodesmata across cell walls connect plant cells

Cytoskeleton only in animal cells!

1. Microtubules2. Microfilaments3. Intermediate filaments– Organizes– Moves cell parts– Reinforces cell shape– Interactions between – motor proteins – microtubules

• cilia, flagella,

– pseudopods • can move cell

Other features!

• Plant cuticle• Protective surface

secretion, limits water loss

• Connect cells of animals– adhering junctions– tight junctions– gap junctions

Plant vs animal cell