5/29/2014 1 1. Plasma membrane - forms the cell’s outer boundary - separates the cell’s internal environment from the outside environment - is a selective barrier - plays a role in cellular communication 2. Cytoplasm - all the cellular contents between the plasma membrane and the nucleus - cytosol - the fluid portion, mostly water - organelles - subcellular structures having characteristic shapes and specific functions
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1. Plasma membrane - forms the cell’s outer boundary - separates the cell’s internal environment
from the outside environment - is a selective barrier - plays a role in cellular communication
2. Cytoplasm - all the cellular contents between the plasma
membrane and the nucleus - cytosol - the fluid portion, mostly water - organelles - subcellular structures having
characteristic shapes and specific functions
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3. Nucleus - large organelle that contains DNA - contains chromosomes, each of which consists of a single molecule of DNA and associated proteins - a chromosome contains thousands of hereditary units called genes
Flexible yet sturdy barrier The fluid mosaic model - the arrangement of
molecules within the membrane resembles a sea of lipids containing many types of proteins
The lipids act as a barrier to certain substances
The proteins act as “gatekeepers” to certain molecules and ions
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Consists of a lipid bilayer - made up of phospholipids, cholesterol and glycolipids
Integral proteins - extend into or through the lipid bilayer
Transmembrane proteins - most integral proteins, span the entire lipid bilayer
Peripheral proteins - attached to the inner or outer surface of the membrane, do not extend through it
Glycoproteins - membrane proteins with a carbohydrate group attached that protrudes into the extracellular fluid
Glycocalyx - the “sugary coating” surrounding the membrane made up of the carbohydrate portions of the glycolipids and glycoproteins
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Some integral proteins are ion channels Transporters - selectively move substances
through the membrane Receptors - for cellular recognition; a ligand
is a molecule that binds with a receptor Enzymes - catalyze chemical reactions Others act as cell-identity markers
The cell is either permeable or impermeable to certain substances
The lipid bilayer is permeable to oxygen, carbon dioxide, water and steroids, but impermeable to glucose
Transmembrane proteins act as channels and transporters to assist the entrance of certain substances, for example, glucose and ions
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Passive processes - substances move across cell membranes without the input of any energy; use the kinetic energy of individual molecules or ions
Active processes - a cell uses energy, primarily from the breakdown of ATP, to move a substance across the membrane, i.e., against a concentration gradient
Steepness of concentration
gradient Temperature Mass of diffusing
substance Surface area Diffusion distance
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Net movement of water through a selectively permeable membrane from an area of high concentration of water (lower concentration of solutes) to one of lower concentration of water
Water can pass through plasma membrane in 2 ways:
1. through lipid bilayer by simple diffusion 2. through aquaporins, integral membrane
proteins
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Osmosis
Solutes are transported across plasma membranes with the use of energy, from an area of
lower concentration to an area of higher Concentration Sodium-potassium pump
The cell cycle is a sequence of events in which a body cell duplicates its contents and divides in two
Human somatic cells contain 23 pairs of chromosomes (total = 46)
The two chromosomes that make up each pair are called homologous chromosomes (homologs)
Somatic cells contain two sets of chromosomes and are called diploid cells
Interphase - the cell is not dividing - the cell replicates its DNA - consists of three phases, G1, S, and G2,
replication of DNA occurs in the S phase Mitotic phase - consists of a nuclear division (mitosis) and a cytoplasmic division (cytokinesis) to form two identical cells
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Prophase - the chromatin fibers change into chromosomes
Metaphase - microtubules align the centromeres of the chromatid pairs at the metaphase plate
Anaphase - the chromatid pairs split at the centromere and move to opposite poles of the cell; the chromatids are now called chromosomes
Telophase - two identical nuclei are formed around the identical sets of chromosomes now in their chromatin form
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Division of a cell’s cytoplasm to form two identical cells
Usually begins in late anaphase The plasma membrane constricts at its
middle forming a cleavage furrow The cell eventually splits into two daughter
Meiosis occurs in two successive stages: meiosis I and meiosis II
Each of these two stages has 4 phases: prophase, metaphase, anaphase, and telophase
Summary - Meiosis I begins with a diploid cell and ends with two cells having the haploid number of chromosomes; in Meiosis II, each of the two haploid cells divides, the net result is four haploid gametes that are genetically different from the original diploid starting cell