Unit 1: Origins Of Life

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Plasma Membrane

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> Only allows certain molecules to enter or leave cell.
> Separates internal metabolic reactions from external environment.
> Allows cell to excrete wastes and to interact with its environment.

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Membrane Lipids

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- Made mainly of phospholipids. (Phospholipids -> have a polar hydrophilic head and 2 nonpolar hydrophobic fatty acid tails.)
- Phopholipid bilayer- phosolipid heads turn outward, tails stay inward, away from water.
- Eukaryotes contain lipids, called sterols between tails.

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sterols

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Sterol function: makes the membrane more firm and prevents membrane from freezing at low temps.

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Membrane Proteins

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-Integral proteins- Often have carbohydrates attached which act as labels on cell surfaces. Some labels help cells recognize each other and stick together. Integral proteins actively transport molecules into cell. Some act as channels or pores that allow certain substances to pass. Others bind to a molecule on the outside of cell then transport it through the membrane. And others act as sites where chemical messengers (hormones) can attach.
-Other proteins (receptor proteins and transport proteins) extend across the plasma membrane and are exposed to both exterior and interior environments of cell.
-Proteins that extend across the membrane are able to detect environmental signals and transmit them inside of cell.
-Peripheral Proteins- lie only on one side of membrane and are not embedded in it.

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Nucleus

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-Most functions of a eukaryotic cell are controlled by nucleus.
-filled with a jellylike liquid -> nucleoplasm.
-Houses and protects cells’ genetic info.
-Chromatin- DNA exists in the form of long, thin structures when cell is not dividing.
-When a cell is about to divide, DNA condenses to form chromosomes. Chromosomes are structures in the nucleus made of DNA and protein.
-Site where DNA is transcribed into ribonucleic acid (RNA) RNA moves through nuclear pores to the cytoplasm

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nucleoplasm

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Nucleoplasm holds the contents of nucleus and is similar in function to cytoplasm.

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Nuclear Envelope

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-A double membrane that surrounds the nucleus.
-Made up of 2 phospholipid bilayers.
-Covering the surface are tiny, protein-lined holes, which are called nuclear pores.
-Pores provide passageways for RNA and other materials to enter and leave the nucleus.

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Nucleolus

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-Denser area of nucleus
-Site where DNA is concentrated when it is in the process of making ribosomal RNA.

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Ribosomes

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made of protein and RNA
-Small, roughly spherical organelles that are responsible for building protein.
-Does not have a membrane
-Ribosome assembly begins in the nucleolus and is completed in the cytoplasm.
-One large and one small subnit come together to make a functioning ribosome.
-Some are free within the cytosol
-Others are attached to the rough endoplasmic reticulum.

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Mitochondria

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-Tiny organelles that transfer energy from organic molecules to adenosine triphosphate (ATP). ATP ultimately powers most of the cell’s chemical rxns. (Active cells- muscle cells= lots of mitochondria. Not active cells- fat-storing cells, few mitochondria)
-Has an inner and outer phospholipid membrane. Outer membrane separates the mitochondrian from the cytosol. Inner membrane has many folds, called cristae.

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Cristae

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Cristae contain proteins that carry out energy-harvesting chemical rxns.

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Mitochondrial DNA

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-Have their own DNA and can reproduce only by the division of preexisting mitochondria.
-Scientists think mitochondria originated from prokaryotic celld that were incorporated into ancient eukaryotic cells.
-Symbiotic relationship provided prokaryotic invaders with a protected place to live and provide the eukaryotic cell with increased supply of ATP.

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Endoplasmic Reticulum (ER)

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-A system of membranous tubes and sacs, called cisternae.
-Functions primarily as an intracellular highway, a path along which molecules move from one part of the cell to another.

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Rough Endoplasmic Reticulum

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-System of interconnected, flattened sacs covered with ribosomes.
-Produces phospholipids and proteins
-Most abundant in cells that produce large amounts of protein for export. (Digestive glands and antibody-producing cells.)

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Smooth Endoplasmic Reticulum

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-Lacks ribosomes and has a smooth appearance.
-Most cells contain very little smooth ER.
-Builds lipids such as cholesterol.

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Golgi Apparatus

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-System of flattened, membranous sacs.
-Sacs nearest the nucleus receive vesicles from the ER containing newly made proteins or lipids.
-Vesicles travel from one part of the Golgi apparatus to the next and transport substances as they go.
-The stacked membranes modify the vesicle contents as they move along.
-The proteins get “address labels” that direct them to various other parts of the cell. During this modification, the apparatus can add carbohydrate labels to proteins or alter new lipids in various ways.

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Vesicles

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-Small, spherically shaped sacs that are aurrounded by a single membrane and that are classified by their contents.
-Often migrate to and merge with the plasma membrane. As they do, they release their contents to the outside of the cell.

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Lysosomes

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- Vesicles that bud from the Golgi apparatus and that contain digestive enzymes.
-Responsible for breaking down cells when it is time for cells to die.
-Within a cell, lysosomes digest worn-out organelles in a process called autophagy.
-The digestion of damaged or extra cells by the enzymes of their own lysosomes is called autolysis.

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Peroxisomes

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-Similar to lysosomes but contain different enzymes and are not produced by the Golgi apparatus.
-Abundant in liver and kidney cells, where they neutralize free radicals (oxygen ions that can damage cells) and detoxify alcohol and other drugs.
-Named for the hydrogen peroxide they produce when breaking down alcohol and killing bacteria.
-Break down fatty acids, which mitochondria can then use as an energy source.

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Protein Synthesis

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1.) Proteins are assembled by ribosomes on rough ER
2.) Vesicles transport proteins to the Golgi apparatus
3.) Golgi modifies proteins and packages them in new vesicles.
4.) Vesicles release proteins that have destinations outside the cell
5.) Vesicles containing enzymes remain inside the cell as lysosomes, peroxisomes, endosomes, etc.

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Cytoskeleton

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-Acts as a system of internal tracks, on which items move around inside the cell.

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Microtubules

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- Hollow tubes made of protein called tubulin.
-Holds organelles in place,
- maintain a cell’s shape
- act as tracks that guide organelles and molecules as they move within the cells.

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Microfilaments

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Contribute to cell movement, including the crawling of white blood cells and the contraction of muscle cells.

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Intermediate Filaments

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-Rods that anchor the nucleus and some other organelles to their places in the cell.
-Maintain the internal shape of nucleus.

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Cilia and Flagella

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-Hairlike structures that extend from the surface of the cell, where they assist in movement.
-Cilia are short and are present in large numbers on certain cells, flagella are longer and are far less numerous on the cells where they occur.
-Both have a membrane on their outer surface and an internal structure of nine pairs of mircrotubules around two central tubules.

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Centrioles

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- Consists of 2 short cylinders of microtubulesand are situated in the cytoplasm near the nuclear envelope.
-Occur in animal cells, where they organize the microtubules of the cytoskeleton during cell division.