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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
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