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 Fluid mosaic model Membrane is composed of phospholipids, sterols, proteins, and other components Phospholipids drift within the bilayer extracellular environment one layer of lipids membrane protein one layer of lipids cytoplasm

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 Chloroplasts 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! Microtubules Microfilaments 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