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Biology – Kevin Dees
Chapter 6A Tour of the Cell
Biology – Kevin Dees
• The cell is the basic unit of life• Although cells differ substantially from one
another, they all share certain characteristics that reflect a common ancestry and remind us of the unifying theme of evolution
• Three main parts of a cell– Plasma membrane– Cytoplasm– Genetic control
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Biology – Kevin Dees
History of the cell
• First ‘microscopes’ – 1590 - technology• The term ‘cell’ was first coined by Robert
Hooke in 1665.• Little knowledge was gained about cell
structure –function until the 1950’s– WHY???– Technology
Biology – Kevin Dees
Microscopes• Essential tool for studying the cell
– Light microscopes –• Ratio of image size to actual size –
magnification• Measure of clarity – resolution• Many of the essential components of cells
were too small for adequate resolution by a light microscope
– Electron microscopes – much higher magnification and resolution • Electron microscopes made the detailed
study of cell ultrastructure possible
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Biology – Kevin Dees
Biology – Kevin Dees
Comparison of Light , Transmission electron and Scanning Electron microscopy
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Biology – Kevin Dees
Recall, that there are two basic categories of cells:
• Prokaryotic cells – organisms in the Domain Archaea and Bacteria are prokaryotic in structure
• Eukaryotic cells – plants, animals, fungi, etc..
Biology – Kevin Dees
Prokaryotic cells
• Very simple – contain:– Plasma membrane– Cytoplasm– Genetic control
• No nucleus –prokaryotic chromosome is not enclosed in a membrane!!!!!
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Biology – Kevin Dees
Eukaryotic cells
• True nucleus – genetic material is surrounded by membrane.
• Typically larger than prokaryotic cells but still small
• Why are cells small?• Large living things typically do not have
larger cells? Why??
Biology – Kevin Dees
Plasma membrane• Forms a selective barrier to allow the controlled passage
of materials in and out of the cell• Phospholipid bilayer with proteins• Forms the surface area of a cell
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Biology – Kevin Dees
Surface area regulates cell size• Materials must pass in-out of cell.• Must pass through plasma
membrane
Biology – Kevin Dees
Comparison of typical animal and plant cells
• Recall the three components that all share have in common:– Plasma membrane– Cytoplasm– Genetic control
• We are going to survey generalized animal and plant cells– Look for similarities and differences between
the two
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Biology – Kevin Dees
General Animal cell
• Plasma membrane
• Microvilli
• Flagellum
• Cytoplasm
• Mitochondrion
• Cytoskeleton
• Centrosome – pair of centrioles
Biology – Kevin Dees
General Animal cell
• Endoplasmic reticulum– Rough ER– Smooth ER
• Ribosomes
• Golgi complex
• Lysosome
• Peroxisome
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Biology – Kevin Dees
General Animal cell
• Nucleus– Nuclear
envelope– Nuclear pores– Nucleolus– chromatin
Biology – Kevin Dees
General Plant cell
• Cell wall– plasmodesmata
• Central vacuole– Tonoplast-turgor
pressure• Chloroplast
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Biology – Kevin Dees
A closer look at the nucleus
• Nuclear envelope• Nuclear pores
– Nuclear pore complex– Transport of materials
• Nucleolus– Ribosome production
• Genetic material– Chromatin– Chromosomes
• During cell division– Humans – 23 pair of
chromosomes in somatic cells; 23 single in gametes
• Why??????
Biology – Kevin Dees
• Made of ribosomal RNA and proteins– Large and small subunits form ‘sandwich’
• Carry out protein synthesis• Not surrounded by a membrane• Free ribosomes – floating in the cytoplasm
– Synthesize proteins that have a function in the cytoplasm• Bound ribosomes – attached to ER or nuclear envelope
– Synthesize proteins for insertion into cell membranes, lysosomes, or export from cell
A closer look at ribosomes
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Biology – Kevin Dees
• Endomembrane system includes the SER, RER, the nuclear envelope, the Golgi apparatus, various vesicles and vacuoles and the plasma membrane
• SER– Synthesis of lipids,
steroids, phospholipids– Detoxification
• RER– Important in protein
synthesis– produces more
‘membrane’ for the cell• Transport vesicles
A closer look at the endomembrane system
Biology – Kevin Dees
• The cis face is located near the ER– Transport vesicles from the ER move materials to the Golgi
• The trans face is located away from the ER – Gives rise to vesicles which move away from the Golgi
A closer look at the Golgi apparatus
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Biology – Kevin Dees
• Lysosomes – found in animal cells– Membranous sacs of
hydrolytic enzymes for intracellular digestion
• Phagocytosis –creation of food vacuole and subsequent digestion
• Autophagy – recycles cellular components
Biology – Kevin Dees
• Vacuoles - storage sacs– Food vacuoles– Central vacuole
found only in plant cells
• Tonoplastmembrane
• Turgor pressure –water
– Storage of electrolytes
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Biology – Kevin Dees
• Mitochondria– Cristae– Mitochondrial matrix– Free ribosomes and mitochondrial DNA– Site of aerobic cellular respiration and majority of
ATP production
Biology – Kevin Dees
• Chloroplasts – Found in plant cells only
• Site of photosynthesis within the cell• Chlorophyll and other pigments• Chloroplast DNA and ribosomes• Thylakoid membranes• Grana – stacks of thylakoids• Stroma – fluid filled area outside the thylakoids
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Biology – Kevin Dees
Elements associated with the cytoskeleton - Functions for support, motility and
regulation• Centrosome –
animals cells– Pair of centrioles– Creation of the
mitotic spindle used during cellular division
Biology – Kevin Dees
• Cilia
• Flagella
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Biology – Kevin Dees
Cell wall of plants
• Composed of primarily cellulose
• Structure for plant cell• Plasmodesmata
– Connections between plant cells
• Middle lamella – joins adjacent plant cells
Biology – Kevin Dees
Cellular junctions• Plant cells
– Plasmodesmata• Animal cells
– Tight junctions• Continuous seal
– Gap junctions• Communication
between cells– Desmosomes
• ‘rivets’