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Ch. 3: Cells - The Living Units

Terms in this set (38)

cell theory
- cells are basic structural + functional units of life
- activity of an organism depends on activities of its cells
- biochemical activities of a cell are dictated by their sub cellular structures
- the continuity of life has a cellular basis
basic characteristics of cells
- all cells composed mainly of carbon, nitrogen, oxygen, hydrogen
- all cells have same basic parts + some common facts
- generalized human cell contains plasma membrane, cytoplasm + nucleus
plasma membrane composed of
double layer of lipid molecules in which proteins are embedded
phospholipid heads
hydrophilic
line up to face inner and outer surfaces of membrane
phospholipid tails
hydrophobic
line up facing each other in interior of bilayer
phospholipid bilayer
contain glycolipids, cholesterol, lipid rafts
glycolipids
5% of membrane
lipids with attached sugar groups
THEY MAKE CELL POLAR
cholesterol
20% of membrane
helps stabilize membrane
lipid rafts
20% of membrane
platforms for cell receptors needed for cell signaling
integral proteins
type of membrane protein
transmembrane proteins - they cross the whole membrane
make channels that allow for small water-soluble molecules + ions to travel into + out of cell
peripheral proteins
type of membrane protein
not embedded into membrane
FUNCTION AS ENZYMES
cell junctions
places where cells are anchored together
three types: tight junctions, desmosomes, gap junctions
tight junctions
integral proteins between adjacent cells, forming impermeable junction that prevents molecules from passing through extracellular space between cells
desmosomes
mechanical couplings that are scattered along the sides of adjoining cells that prevent their separation + reduce chance of tearing when a tissue is stressed
gap junctions
hollow cylinders of protein between cells that allow selected small molecules + ions to pass between adjacent cells

often used in conduction of action potentials between cells
cell membrane
selectively permeable - allows nutrients to enter cell + waste to leave, but restricts movement of other substances in or out of cell
passive process
requires no energy (ATP) to move substances down their concentration gradient
ex: simple diffusion, carrier-mediated difffusion, channel-mediated diffusion, osmosis
high concentration to low concentration
active process
requires energy (ATP) to move substances across cell membrane
ex: primary active transport, secondary active transport, vascular transport, endocytosis
diffusion
movement of molecules down a concentration gradient
rate of diffusion
dependent on size of molecule + temperature
simple diffusion
diffusion through plasma membrane, without using a channel or carrier
restricted to movement of very small molecules or lipids
facilitated diffusion
sugars, amino acids, or ions are moved through plasma membrane by binding to protein carriers in membrane or by moving through channels
osmosis
diffusion of water
active transport
moves substances AGAINST their concentration gradient
requires energy generally in form of ATP
low concentration to high concentration
primary active transport
uses ATP to move substances against their concentration gradient
ex: Na+/K+ pump --> 3 Na+ molecules go out of cell as 2 K+ molecules come in (MUST KNOW DIAGRAM)
secondary active transport
energy used to transport molecules is from energy stored in ionic gradients created by primary active transport
roles of cell membrane receptors
contact signaling
chemical signaling
voltage-gated membrane channel proteins
contact signaling
involves TOUCH between membrane receptors of NEIGHBORING cells to facilitate recognition between cells
chemical signaling
involves the binding of a chemical signal to a membrane receptor, resulting in initiation of cellular responses
voltage-gated membrane channel proteins
in excitable tissues (like neurons or muscle cells) certain ion channels in cell membrane open or close in response to a change in membrane potential, allowing electrical signaling between cells
chromatin
chromatin = DNA (30%) + histone proteins (60%) + RNA (10%)

when a cell is preparing to divide chromatin condenses into dense, rodlike chromosomes

DNA WRAPPED AROUND HISTONE PROTEINS
cell growth + replication
two major time periods: interphase (growth period/DNA replication) + cell division (mitosis/cytokinesis)
subphases of interphase
gap 1 phase (G1): cell is synthesizing proteins + actively growing
S1 phase: DNA is replicated
gap 2 phase (G2): enzymes + other proteins are synthesizes and distributed throughout the cell
cell division
mitosis - division of the nucleus
cytokinesis - division of the cytoplasm
mitosis
central dogma
DNA replicated --> transcribed into mRNA strand --> translated into proteins
practice problem **
DNA: 5': TACAGTCCGTAGATC: 3'
mRNA: ?
tRNA: ?
protein sequence: ?
terms to know **
DNA replication
transcription
translation
mitosis
cell cycle
chromatin structure
the nucleus
osmosis
diffusion
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