Download investigation 2

INVESTIGATION 2
Structure and Function of the Cell
By: Madison Shelpuk
&
Connor Erickson
Internal Organization
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Cells contain a variety of internal structures called organisms.
Organelle is a cell component that performs specific functions for the cells.
An entire cell is surrounded by a thin membrane, called cell membrane.
Inside the cell are a variety of organelles, which are surrounded by their own membranes.
Nucleus is the large organelle near the center of the cell.
Eukaryotes are organisms whose cells contain a membrane- bound nucleus and other organelles.
Prokaryotes are unicellular organisms that lock a membrane- bound nucleus and other organelles.
Cell Membrane
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Selectively permeable is when the cell membrane controls the ease which substances easily crosses the membrane.
The structure of the cell membrane depends on the functions the cell performs.
Membrane Lipids
•One of the major types of liquids in the cell membrane is phosphoric.
•Cells are bathed in an aqueal or watery environment. Since the inside of the cells is also an aqueous environment, both
sides of the cell membrane are surrounded by water molecules.
Membrane Proteins
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Peripheral proteins are proteins that are attached to the surfaces of the cell membrane. They are located on both the interior
surface and the exterior surface of the cell membrane.
Integral proteins are proteins that are embedded in the bi- layer.
Because the cell membrane is selectively- permeable, cells must have mechanisms for transporting molecules through the
lipid bi-layer.
Fluid Mosaic Model of the Cell
Membranes
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Scientists use the fluid mosaic model to describe the cell membrane.
The lipid bi-layer behaves more like a fluid than a solid.
Organelles
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Between the cell membrane and the nucleus lies the cytoplasm, which contains the various organelles of the cell.
Cytosol are organelles that are bathed in a gelatin- like aqueous fluid.
The name organelle comes from the idea that these structures are to cells what an organ is to the body (hence the name
organelle, the suffix -elle being a diminutive). Organelles are identified by microscopy, and can also be purified by cell
fractionation.
Mitochondria
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Mitochondria are scattered throughout the cytosol, which are relatively large organelles.
Mitochondria are he sites of chemicals reactions that transfer energy from organic compounds to the ATP.
Cristae are the inner membrane, that has many long folds. The Cristae greatly enlarge the surface area of the inner
membrane, providing more space for the chemical reactions that occur in the mitochondria.
Ribosomes
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Most numerous organelles in most cells.
Unlike most organelles, ribosomes are not surrounded by a membrane.
They are made up of proteins and RNA.
Inside the cell’s nucleus, proteins and RNA are packaged into ribosomes, which are transported to the
cytosol.
Some ribosomes remain free within the cytosol, while some become attached to an organelle called the
endoplasmic reticulum.
Proteins to be used within the cytosol are produced on the ribosomes that are free in the cytosol. Proteins
exported from the cytosol are produced on the ribosomes that are attached to the endoplasmic reticulum.
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Endoplasmic Reticulum
• ER is a system of membranous tubules and sacs.
• ER functions as a path along which molecules move from one part of the
cell to another.
• The amount of ER inside a cell depends on the cell’s activity.
• A cell usually contains two types of ER:
– Smooth ER:
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Involved in the synthesis of steroids in gland cells, regulation of calcium levels, and breakdown of toxic
substances.
– Rough ER
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Prominent in cells that make large amounts of proteins to be exported from the cell.
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Golgi Apparatus
• Golgi Apparatus is the processing, packaging,
and secreting organelle of the cell.
• Golgi apparatus is a system of membranes.
• Working with the ER, the golgi apparatus
modifies proteins for exporting the cell.
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Lysosomes
• Small, spherical organelles that enclose hydrolytic enzymes within single
membranes. These enzymes can digest proteins, carbohydrates, lipids,
DNA, and RNA. They also digest old organelles, viruses, and bacteria.
• Lysosomes are common in animals, fungi, and protists, but not in plant
cells.
• Lysosomes play a role during early development in the embryo.
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Cytoskeleton
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The structure of a cell.
Not surrounded by membranes.
Participates in movement of organelles within the cytosol.
There are two major components of the cytoskeleton:
– Microfilaments
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Threads made of a protein called actin
Contribute to cell movement and play a role in the contraction of muscle cells.
– Microtubles
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Largest strands, hollow tubes.
When a cell is about to divide, bundles of microtubles come together and expand across the cell. These
bundles are called spindle fibers which assist in the movement of chromosomes during cell division.
Cilia and Flagella
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Cilia and Flagella are hairlike organelles that extend from the surface of the cell,
where they assist in movement.
They can be found in many eukaryotic cells.
When these organelles are short and numerous, they are cilia. The movements of
cilia propel the tiny organisms through the water to find food or escape from
predators.
When these organelles are long and less numerous, they are flagella. On many
cells, including sperm cells, only one flagella is present. By whipping back and
forth, flagella can swiftly propel around.
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Nucleus
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The nucleus is often the most prominent structure within a eukaryotic cell.
It maintains it’s shape with the help of the nuclear matrix.
The nucleus is surrounded by a double membrane called the nuclear envelope.
Inside the nuclear envelope are strands of chromatin, a combination of DNA and
protein. When a cell is about to divide, the chromatin strands coil up and become
densely packed, forming chromosomes.
The nucleus stores hereditary information in its DNA.
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Plant Cells - Cell Wall
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Plant cells are covered by a rigid cell wall that lies outside the cell membrane. It is rigid which
helps support and protect the plant.
The walls contain long chains of cellulose, which is embedded in proteins and other
carbohydrates and harden the entire structure. Pores in the wall allow ions and molecules to
exit and enter the cell.
When a plant cell is being formed, a primary cell wall develops outside the membrane which
may expand more and more and when it reaches full size, a second wall may develop.
When you hold a piece of wood, you are touching secondary walls. The cells inside the walls
have died and disintegrated.
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Vacuoles
• Vacuoles are another common characteristic of plant cells.
• Vacuoles are fluid-filled organelles which store enzymes and
metabolic wastes.
• They can store some wastes which are toxic and must be kept
away from the rest of the cell.
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Plastids
• Another distinguishing feature of plant cells, the plastids are organelles
that are surrounded by two membranes and contain DNA. Some plastids
store starch or fats, while others contain pigments, which absorb visible
light.
• The most familiar type of plastid is the chloroplast, which encloses a
system of sacs called thylakoids.
• Chloroplasts convert the energy of sunlight into chemical energy. This
conversion occurs during photosynthesis.
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