LIFESCI 7A Lecture Notes - Lecture 2: Non-Coding Rna, Membrane Protein, Central Dogma Of Molecular Biology
WEEK 2:
1.3: The Cell
○ cell: The simplest self-replicating entity that can exist as an independent unit of life.
■ contain a stable blueprint of (genetic) information in molecular form
■ have a discrete boundary (membrane) that separates the interior of the cell from its
external environment
■ have the ability to harness materials and energy from the environment.
● Nucleic acids store and transmit information needed for growth, function, and reproduction.
○ deoxyribonucleic acid (DNA): A linear polymer of four subunits; the information archive in all
organisms.
○ Proteins: The key structural and functional molecules that do the work of the cell, providing
structural support and catalyzing chemical reactions. The term “protein” is often used as a
synonym for “polypeptide.”
○ ribonucleic acid (RNA): A molecule chemically related to DNA that is synthesized by proteins
from a DNA template.
○ transcription: The synthesis of RNA from a DNA template.
○ translation: Synthesis of a polypeptide chain corresponding to the coding sequence present in
a molecule of messenger RNA.
○ central dogma: The theory that information transfer in a cell usually goes from DNA to RNA to
protein.
○ gene: The unit of heredity; the stretch of DNA that affects one or more traits in an organism,
usually through an encoded protein or noncoding RNA.
■ the DNA sequence that corresponds to a specific protein product.
○ replication: The process of copying DNA so genetic information can be passed from cell to cell
or from an organism to its progeny.
● Membranes define cells and spaces within cells
○ plasma membrane: The membrane that defines the space of the cell, separating the living
material within the cell from the nonliving environment around it.
○ nucleus (of a cell): The compartment of the cell that houses the DNA in chromosomes.
■ prokaryote: An organism whose cell or cells does not have a nucleus. Often used to
refer collectively to archaeons and bacteria.
■ eukaryote: An organism whose cells have a true nucleus.; include eukaryotes and
single celled protists
■ cytoplasm: The contents of the cell other than the nucleus.
○ Bacteria (prokayrotic): One of the three monophyletic domains of life, consisting of single-celled
organisms with a single circular chromosome but no nucleus that divide by binary fission and
differ from archaeons in many aspects of their cell and molecular biology.
○ Archaea (prokaryotic): One of the three domains of life, consisting of single-celled organisms
with a single circular chromosome and no true nucleus that divide by binary fission and differ
from bacteria in many aspects of their cell and molecular biology.
■ Can flourish under seemingly hostile conditions
○ Eukarya (eukaryotic): The eukaryotes; one of the three domains of life, in which cells have a
true nucleus and divide by mitosis.
● Metabolism converts energy from the environment into a form that can be used by cells.
○ Organisms acquire energy from just two sources—the sun and chemical compounds; chemical
reactions to break down molecules, releasing energy
○ all organisms use energy stored as ATP
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■ adenosine triphosphate (ATP): The molecule that provides energy in a form that all
cells can readily use to perform the work of the cell. ATP is the universal energy
currency for all cells.
○ Many metabolic reactions are similar in different organism (suggests that metabolism developed
very early on in evolution because it’s so fundamental)
5.1: Structure of Cell Membranes
● Lipids are hydrophoic molecules
○ Instead of being made up by building blocks like the other three macromolecules, lipids all share
a property: being hydrophobic
■ Defined by a property rather than structure; very diverse
○ triacylglycerol: A lipid composed of a glycerol backbone and 3 fatty acids.
■ Used for energy storage
■ fatty acid: a long chain of carbon atoms attached to a carboxyl group (–COOH) at one
end
● saturated: Describes fatty acids that do not contain double bonds; the maximum
number of hydrogen atoms is attached to each carbon atom, “saturating” the
carbons with hydrogen atoms.
● metabolism: The chemical reactions occurring within cells that convert
molecules into other molecules and transfer energy in living organisms.
● unsaturated: Describes fatty acids that contain carbon–carbon double bonds.
■ glycerol: A 3-carbon molecule with OH groups attached to each carbon.
○ van der Waals forces: The binding of temporarily polarized molecules because of the attraction
of opposite charge
■ Because of van der waals forces, saturated, long fatty acids have a much higher melting
point than unsaturated and short fatty acids
● MORE interactions and closer together=higher melting point
○ Steroid: A type of lipid (ex: cholesterol).
○ Phospholipid: A type of lipid and a major component of the cell membrane.
● Cell membranes are composed of two layers of lipids
○ Phospholipids (cont).: Made up of gycerol backbone attatched to a phosphate group (hydrophilic
head) and two fatty acid chains (hydrophobic tail)
■ amphipathic: Having both hydrophilic and hydrophobic regions.
■ In aqueous solution, phosophoipids come together so that the heads are facing outward
to the water and the tails are inward; depending on size of head/tail, they can form
● micelle: A spherical structure in which lipids with bulky heads and a single
hydrophobic tail are packed.
● bilayer: A two-layered structure of the cell membrane with hydrophilic “heads”
pointing outward toward the aqueous environment and hydrophobic “tails”
oriented inward, away from water.
● Liposomes: looks like a double-layered sphere
● Cell membranes are dynamic: continually moving, forming, and re-forming during the lifetime of a cell.
○ fluid: Describes lipids that are able to move in the plane of the cell membrane.
■ Tighter packing of lipids reduce mobility; saturated fatty tails are less fluid than
unsaturated
○ cholesterol: An amphipathic lipid that is a major component of animal cell membranes
■ Hydrophilic: hydroxyl group (-OH); hydropphobic (hydrocarbon chain+rings)
■ Regulates membrane fluidity depending on temp
● High temps: reduces mobility bc rigid ring structure interacts with fatty tails
● Low temps: acts as spacer that prevents lipids from packing too tightly
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