Cell Biology - The Living Cell (1989)

blue um imagine yourself Gliding Over A Quiet Pond you are literally surrounded by life [Music] let's do it [Music] [Music] simple or complex all of these living things have one thing in common they are all made of cells cells of complex organisms are specialized for different tasks these create tiny pores that open and close to allow a leaf to exchange gases with the atmosphere examining other plant parts turns up surprises like these cells the end cell releases a sticky glue that discourages stem climbing insects cross-sectioning a stem shows the honeycomb of cells that support the plant and the various kinds of specialized cells that make up its plumbing system If plants are flowering it's possible to explore the cells that make up the flower these stamen hairs are actually bead-like chains of large cells keep within a flowers female organ the ovary is the cell that will begin a new plant an egg cell plant cells have two kinds of structures not found in animal cells one is the cell wall cell walls give plants their amazing strength and resiliency the other structure is not found in animal cells are rounded bodies called plastids chromoplasts are plastids that give fruits and flowers their color leukoplasts are placids that store carbohydrates the green plastids found in leaf cells are chloroplasts the bodies where photosynthesis occurs through photosynthesis plant nutrients are produced and oxygen released [Music] so plastids and cell walls distinguish plant cells from animal cells but animals have more kinds of specialized cells like blood cells bone cells muscle cells nerve cells liver cells skin cells over 200 kinds of cells in a vertebrate animal in small clear invertebrates many kinds of animal cells can be examined in their live state [Music] a Daphne's heart pumps clear circulatory fluid through its body the blood cells we see are leukocytes white blood cells they have the same function as leukocytes in humans providing immunity and engulfing harmful bacteria Daphne as appendages are moved by muscle cells the same kind found in human skeletal muscles other cells tune in on touch or smell and others on light all of these specialized cells in complex animals originate from a single cell a fertilized egg sharing daphnia's world are single cells that live independently as individual organisms these protists are usually classified in the Kingdom of their own separate from plants and animals protists are complex cells that can move about respond and feed there are thousands of different kinds each with its own methods of feeding and locomotion [Music] a cell whether from a plant animal or protist is organized into three distinct regions nucleus cytoplasm and the plasma membrane by controlling the molecular traffic entering and leaving the cell the plasma membrane allows a cell to maintain a stable internal environment that is chemically different from its surroundings the plasma membrane encloses the cytoplasm which includes everything inside the cell but the nucleus it's made up partly of a watery fluid called the cytosol containing a complex mix of dissolved substances suspended in the cytosol are a great number of small bodies of various kinds called organelles identifying these organelles with the electron microscope and determining their functions has been one of the great achievements of Cell Biology what looked like beans dancing about in the cytoplasm under the light microscope showed complex inner structure when examined with the electron microscope these are mitochondria energy transforming organelles found in all plant animal and protist cells within a mitochondrion building block molecules are broken down using oxygen energy from these compounds is transferred to the energy carrier molecule ATP the vast numbers of ATP molecules generated in mitochondria provide most of the energy for the chemical reactions that take place in a cell another cytoplasmic organelle called a lysosome makes available some of the molecules used for energy the Interior Space of a lysosome is filled with digestive enzymes that break down large food molecules releasing their building blocks which can then be picked up by mitochondria and oxidized in protests that engulf food lysosomes dump their enzymes into food vacuoles where digestion takes place within every living cell are networks of membranes that partition the cytoplasm and compartmentalize the cell's production of proteins and other products for example surrounding the nucleus can be seen folded membranes embedded in these membranes are tiny particles called ribosomes ribosomes are organelles which Aid in the manufacture of new cell proteins this ribosome studded membrane surrounding the nucleus is called the endoplasmic reticulum connected with the endoplasmic reticulum is a region of densely folded membrane called the Golgi apparatus membranes of the Golgi apparatus confuse with the cell's outer membrane allowing products to be exported out of the cell examining cells under the light microscope scientists found it hard to see how certain cells could be both flexible and still maintain their General shapes a major Discovery using the electron microscope was that cytoplasm contained a hidden framework of organelles a sort of cytoskeleton made of protein filaments and tubules one kind of protein filament is found in tough but flexible skin cells tagged with fluorescent dyes these protein filaments appear like this the protein molecules are twisted into cable-like girders while protein filaments give cells shape other proteins are involved in cell movement in muscle cells two kinds of protein filaments interact to produce a contraction there is a central filament made up of myosin molecules which are long thin proteins with bulbous ends or heads surrounding these fibers are bundles of filaments made from a different kind of elongated protein molecule actin using energy supplied by ATP from nearby mitochondria the myosin heads Bend producing a sliding displacement of the surrounding actin filaments the sliding sections of these protein filaments are the moving bands seen in muscle cells [Music] other cytoplasmic proteins form delicate tubular structures these sliding microtubules are major players in almost all cell movements whether they move materials around inside of a cell or move the whole cell but the most impressive action is produced by the microtubules that power cilia the whip-like hairs that Propel single-celled organisms through the water [Music] a section through a group of cilia shows the arrangement of microtubules that slide on each other to produce the bending action this wheel-like pattern of microtubules is the same in all cilia whether they provide Locomotion for a single-celled organism or move dust and mucus away from the lungs in the respiratory tract of a human the activities of the cytoplasm are largely controlled from a third major cell region the nucleus housed safely within it are giant information molecules the cell's DNA when a cell is not reproducing its DNA is more or less evenly distributed throughout the nucleus and in constant chemical communication with the cytoplasm pores in the nuclear membrane allow this two-way traffic [Music] when a cell is getting ready to divide its DNA coils up and forms structures first seen in cells that have been stained chromosomes duplicate sets of chromosomes are parceled out giving each cell a complete set of genetic instructions when cells are not dividing the only obvious feature seen within the nucleus is a small dark staining body called the nucleolus the nucleolus manufactures the main components of ribosomes [Music] the fact that all nucleated cells whether plant animal or protist are fundamentally alike suggests that they all evolved from a common type of ancestral cell but what were early cells like there is evidence of cellular life in layered fossils dated at around three and a half billion years fossils were probably formed by layers of organisms resembling bacteria bacteria are prokaryotic cells cells without nuclei they have a cell wall but few organelles of the kind found in cells with nuclei eukaryotic cells it now appears that prokaryotic cells like these were the major form of life for around 2 billion years the question is how did the giant leap in cell complexity from prokaryote to Eukarya come about just how did cells acquire their organelles an interesting theory has been proposed to explain the origins of such important organelles as chloroplasts and mitochondria the theory hinges on the idea of symbiosis the living together of two different kinds of life a common example is seen in this giant cell stentor these trumpet-shaped protists often cluster on underwater stems and are easily visible to the naked eye the green color is due to thousands of algae cells living in stentor cytoplasm in this protected environment they share food which they make by photosynthesis with their large host cell it's an example of cooperation between cells in which both kinds benefit such relationships must also have occurred when the first cells with nuclei the first eukaryotic cells appeared we can imagine primitive nucleated cells playing host to a variety of smaller bacteria-like organisms some of these prokaryotes made food by photosynthesis others supplied energy by breaking down food molecules and others yet joined in over time providing Locomotion in exchange for the nutrients and protection offered by a larger host cell in this way the symbiotic Theory May account for the presence of chloroplasts mitochondria cilia perhaps some of the other organelles found in nucleated cells but however they originated microfossils show that by around a billion years ago the Waters of planet Earth were teeming with a new kind of larger cell a cell with a nucleus and organelles [Music] colonies of cells appeared The evolutionary bridge between single cells and early multicellular life forms and from this pool of primitive organisms sprang the varieties of life that inhabit Earth today animals plants and modern forms of single cell life [Music]