All About Cells
This post includes notes about cells!
Acronyms:
DNA: deoxyribonucleic Acid
ATP: Adenosine triphosphate
Cell Wall:
Definition: A cell wall is a thick, rigid, non-living layer that surrounds the cell membrane in plants and fungus only. It’s made of a tough material called cellulose.
Function: It helps protect and support the cell and control the amount of water entering the cell.
Cell Membrane:
Definition: A cell membrane is a thin, skin-like, flexible membrane that surrounds the cell.
Function: Cell membrane allows nutrients into the cell and to allow wastes leave the cell. It also helps hold the cell together.
Solutions:
Hypertonic Solutions: (high) When a cell is placed in a hypertonic solution, the water diffuses out of the cell, causing the cell to shrivel.
Hypotonic Solutions: (low) When a cell is placed in a hypotonic solution, the water diffuses into the cell, causing the cell to swell and possibly explode.
Isotonic Solutions: (equal) When a cell is placed in an isotonic solution, the water diffuses into and out of the cell at the same rate. The fluid that surrounds the body cells is isotonic.
Nucleus:
Definition: A nucleus is a dark, spherical structure often found near the centre of the cell.
Function: Nucleus controls the cell’s activities by sending chemical messages to various cell structures.
Details: The cell nucleus is enclosed by a nuclear membrane, which controls what enters and leaves the nucleus. The nucleus also contains a nucleolus, where ribosomes are made.
Mitochondria (mitochondrion):
Definition: Mitochondria is a smooth, sausage shaped organelle with interior hollow canals.
Function: It provides cells with energy.
Chloroplast:
Definition: A smooth, egg shaped organelle with interior pouches that contain the green pigment chlorophyll.
Function: It uses sunlight from the Sun to make carbohydrates during photosynthesis.
E.R. (endoplasmic reticulum)
Definition: The endoplasmic reticulum may be rough or smooth. It’s said to be rough when it has many ribosomes attached to its surface.
Function: Materials are transported through these canals to differ parts of the cell or outside of the cell.
Golgi Apparatus
Definition: Golgi apparatus looks like a stack of pancakes. It’s a storage for protein.
Function: When it’s packed with protein, it moves toward the cell membrane and attaches itself to the membrane. It releases vesicles that are filled with protein. The protein can be used inside or outside of the cell.
Ribosome
Definition: Ribosome put protein together and work with golgi apparatus.
Function: produce protein.
Proteins
proteins are made of amino acids. They are important for muscle building, the immune system, and they act as enzymes since enzymes are made of proteins.
Vacuoles
Definition: Vacuoles are smooth, balloon-like structures filled with clear liquid.
Function: Vacuoles are storage places for surplus food, waste, and other substances that the cell cannot use right away.
Vesicles
Definition: Vesicles are tiny sacs that transport material within or outside the cell.
Function: Transport vesicles help move materials, such as proteins and other molecules, from one part of a cell to another.
Lysosomes
Lysosomes are sacs that contain protein. It’s made by the vesicles from golgi apparatus.
They can break down large molecules and other cell parts. Small molecules can be re-used as building blocks. Damaged and worn-out cells are destroyed by their own lysosomes.
Diffusion & Osmosis
Diffusion: particles in a concentrated area spread out into areas where there are fewer particles.
Osmosis: The diffusion of solvent through a selectively permeable membrane is called osmosis.
Selectively permeable: a part of the material can cross.
Permeable: a membrane that lets all materials cross.
Impermeable: a membrane that lets nothing cross.
Multicellular: live in a variety of environments, eat a variety of foods, able to grow large, more complex bodies.
Unicellular: cannot grow very large, take all materials through the cell membrane, and live in watery, food-rich surroundings.
Active Transport
Active transport:
Definition: The movement of molecules across a cell membrane from a region of lower concentration to a region of higher concentration—against the concentration gradient. It requires cell energy.
Function: Particles move from an area of low concentration to an area of high concentration. This reverses the movement caused by diffusion.
Carrier proteins:
Definition: They control substances entering and leaving the cell during active transport.
Function: The carrier protein attracts the substance, moves it through the membrane, and releases it on the opposite side.
ATP (Adenosine triphosphate)
Definition: It is the main energy currency of the cell.
Function: ATP is the main carrier of energy that is used for all cellular activities. When ATP is hydrolyzed and converted to adenosine diphosphate (ADP), energy is released.
Sodium/Potassium Pump
Definition: this is a protein pump found in the cell membrane.
Function: helps maintain a resting potential. (The cell is more negative inside.)
Details: the pump is moving against the concentration gradient. So this requires ATP energy.
Process: 1. Open on the intracellular side then bind 3 sodium ions.
2. ATP transfers its phosphate to the protein. When the protein is phosphated,
it changes its configuration so that it opens to the extracellular side.
3. 2 potassium ions bind to the pump.
4. The phosphate group is released from the protein. So the potassium is inside
again.
Endocytosis
Definition: The process by which cells take in materials.
The three types of endocytosis:
Phagocytosis: The cell consumes a large food particle or bacteria.
Pinocytosis: The cell engulf in fluid that contains solute particles and nutrients.
Receptor mediated endocytosis: the cell has receptors that attach themselves to specific molecules that can fit into the hook of the receptor.
Exocytosis
The cell uses vesicles to export materials out of the cell
Mitosis
Definition: During cell division, the genetic material duplicates and then divides into two identical sets of chromosomes.
Chromosomes:
Definition: become visible only when a cell is about to divide. Chromosomes contain DNA (deoxyribonucleic acid).
Duplicate at INTERPHASE
Placed in the middle at METAPHASE
Pulled apart at ANAPHASE
Form two new nuclei at TELOPHASE
Spindles+centriole
Phases of mitosis:
Prophase (“pro” for “beginning”): DNA condenses into chromosome, nuclear envelope disappears.
Metaphase (“m” for “middle”): Identical chromosomes (sister chromatids) align at the center of the cell (equatorial plate). Sister chromatids are held together by a centromere.
Anaphase (“a” for “away”): Centromere divide (one for each chromatid). Sister chromatids separate. Microtubules form spindle fibers that attach to the centromere of each sister chromatids pulling them to opposite ends of the cell. The cells become elongated.
Telophase: Chromatids arrive at opposite poles of the cell.
Description: The very first step is prophase. The nucleus is still there and it’s going to do way later on. The chromosomes are condensing (thickening and visible). The next stage is metaphase. The chromosomes line up in the middle of the cell. The nucleus has been disassembled, it’s no longer there. In anaphase, the chromosomes move away, they are moving to opposite sides of the cell. Spindles are the fibres that help move the chromosomes to the ends. The last stage of mitosis is telophase, where the chromosomes are at the complete opposite ends and new nuclei are forming on each side to make these two cells. Cytokinesis is responsible for the final separation into two cells by splitting the cytoplasm.
Other phases in the cell cycle:
Interphase (before mitosis): the cell is getting ready to divide. It grows in size and all DNA is replicated.
Cytokinesis (after mitosis): cell membrane pinches inward to divide the cytoplasm forming two daughter cells that are genetically identical to the parent cell.
Daughter cells: The two new cells formed by the division.
Carcinogens:
Definition: the factors that cause cancers.
Examples: chemicals, radiation, inherited factors, certain viruses and repeated damage to the body
Cell Theory
All organisms are made of cells.
Cells are the basic unit of life.
Every cell comes from a pre-existing cell (that happens because of regeneration and mitosis)
Specialized Cells (Cell Specialization):
Cell differentiation: the process of a cell becoming a particular type of cell
A stem cell: an unspecialized cell. It has the potential to become any type of cell.
Embryonic stem cells: come from human embryos (either from umbilical cords, placenta or from aborted embryos).
Adult stem cells: There are some in skin, blood and neural tissues.
Note that this only applies to multicellular organisms.
Examples:
Nerve cells have long, branched fibers running from the main part of the cell to carry nerve signals to different parts of the body.
Red blood cells have a thin, disklike shape to pick up large amounts of oxygen (the bigger the surface area, the easier)
Water-conducting cells of a plant are tubelike, with thick walls and a network of holes that let water pass through them easily
Onion skin cells are flat and brick-shaped, so they can fit closely together to form a continuous protective layer.
Balchandani, V. (1999). Sciencepower 8. Toronto, Ontario: McGraw-Hill Ryerson.
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