Chapter 3 cells Flashcards
cell theory
The cell is the smallest structural and functional living unit
all cells come from existing cells
Organismal functions depend on individual and collective cell functions
Biochemical activities of cells are dictated by their specific subcellular structures
Continuity of life has a cellular basis
membrane lipids
75% phospholipids (lipid bilayer)
5% glycolipids
20% cholesterol
glycolipids
for cell recognition
Lipids with polar sugar groups on outer membrane surface
cholesterol
Increases membrane stability and fluidity
Integral proteins
Firmly inserted into the membrane (most are transmembrane) Functions: Transport proteins (channels and carriers), enzymes, or receptors
tight junctions
Prevent fluids and most molecules from moving between cells
Impermeable junctions prevent molecules
from passing through the intercellular space.
Examples: kidneys, , bile duct
Desmosomes
Rivets” or “spot-welds” that anchor cells together
structure support, keep cell from pulling apart
gap junctions
Transmembrane proteins form pores that allow small molecules to pass from cell to cell
Communicating junctions allow ions and small mole-cules to pass
For electrical synapses (not in skeletal muscle)
For movement of ions
Passive processes
No cellular energy (ATP) required
Substance moves down its concentration gradient
diffusion, facilitated diffusion, osmosis
active processes
Energy (ATP) required
Occurs only in living cell membranes
What determines whether or not a substance can passively permeate a membrane
Lipid solubility of substance
( easier to remember: If water soluble or polar, simple diffusion won’t work)
Channels of appropriate size
Carrier proteins
facilitated diffusion
Certain lipophobic molecules (e.g., glucose, amino acids, and ions) use carrier proteins or channel proteins, both of which: Exhibit specificity (selectivity) Are saturable; rate is determined by number of carriers or channels Can be regulated in terms of activity and quantity
Facilitated Diffusion Using Carrier Proteins
Transmembrane integral proteins transport specific polar molecules (e.g., sugars and amino acids)
Binding of substrate causes shape change in carrier
Facilitated Diffusion Using Channel Proteins
Aqueous channels formed by transmembrane proteins selectively transport ions or water
Two types:
Leakage channels
Always open
Gated channels
Controlled by chemical or electrical signals
osmosis
Movement of solvent (water) across a selectively permeable membrane
Water diffuses through plasma membranes:
Through the lipid bilayer
Through water channels called aquaporins (AQPs)
Membrane permeable to both solutes and water
Solute and water molecules move down their concentration gradients
in opposite directions. Fluid volume remains the same in both compartments
Membrane permeable to water, impermeable to solutes
Solute molecules are prevented from moving but water moves by osmosis.
Volume increases in the compartment with the higher osmolarity.
tonicity
The ability of a solution to cause a cell to shrink or swell
isotonic
A solution with the same solute concentration as that of the cytosol
remains same
hypertonic
A solution having greater solute concentration than that of the cell, cell loses water and shrinks
hypotonic
A solution having lesser solute concentration than that of the cell, cell swells and can lysis
Two types of active processes
Active transport
Vesicular transport
Both use ATP to move solutes across a living plasma membrane
Active Transport
Requires carrier proteins (solute pumps)
Moves solutes against a concentration gradient
Primary Active Transport
Energy from hydrolysis of ATP causes shape change in transport protein so that bound solutes (ions) are “pumped” across the membrane
na k pump
Secondary Active Transport
Depends on an ion gradient created by primary active transport
Energy stored in ionic gradients is used indirectly to drive transport of other solutes
Cotransport
Cotransport—always transports more than one substance at a time
Symport system
Two substances transported in same direction
Antiport system
Two substances transported in opposite directions
Vesicular Transport
Transport of large particles, macromolecules, and fluids across plasma membranes
Requires cellular energy (e.g., ATP)
Exocytosis
Exocytosis—transport out of cell
endocytosis
transport into cell
Receptor mediated vesicular
phagocytosis and pinocytosis
selective
Transcytosis
Transcytosis—transport into, across, and then out of cell
Substance (vesicular) trafficking
Substance (vesicular) trafficking—transport from one area or organelle in cell to another
Phagocytosis
Phagocytosis—pseudopods engulf solids and bring them into cell’s interior
Macrophages and some white blood cells
pinocytosis
Fluid-phase endocytosis (pinocytosis)—plasma membrane infolds, bringing extracellular fluid and solutes into interior of the cell
Nutrient absorption in the small intestine
exocytosis
Hormone secretion Neurotransmitter release Mucus secretion Ejection of wastes vesicle binds to membrane, ruptures, spills contents out
membrane potential
Separation of oppositely charged particles (ions) across a membrane creates a membrane potential (potential energy measured as voltage)
resting membrane potential
Voltage measured in resting state in all cells
Results from diffusion and active transport of ions (mainly K+)
and na
Generation and Maintenance of RMP
The Na+ -K+ pump continuously ejects Na+ from cell and carries K+ back in
Some K+ continually diffuses down its concentration gradient out of cell through K+ leakage channels
Membrane interior becomes negative (relative to exterior) because of large anions trapped inside cell
Roles of Membrane Receptors
contact signalling
chemical signaling
g protein linked recptors
contact signaling
Contact signaling—touching and recognition of cells; e.g., in normal development and immunity
chemical signaling
Chemical signaling—interaction between receptors and ligands (neurotransmitters, hormones and paracrines) to alter activity of cell proteins (e.g., enzymes or chemically gated ion channels)
g protein linked receptors
ligand binding activates a G protein, affecting an ion channel or enzyme or causing the release of an internal second messenger, such as cyclic AMP
(cascade reactions)
cell cycle
Defines changes from formation of the cell until it reproduces
Includes:
Interphase
Cell division (mitotic phase)
interphase
Period from cell formation to cell division
Nuclear material called chromatin
Four subphases:
G1 (gap 1)—enzymes for dna rep
G0—gap phase in cells that permanently cease dividing (QUIESCENT)
S (synthetic)—DNA replication
G2 (gap 2)—preparation for division (enzymes) spindle fiber
mitosis
growth repair, everywhere
meiosis
sexual reproduction, making gametes, reproductive organs
cell division
mitosis four stages,
prophase, metaphase, anaphase, telophase
dna replication
helicase unwinds dna
DNA polymerase only works in one direction
Continuous leading strand is synthesized
Discontinuous lagging strand is synthesized in segments
DNA ligase splices together short segments of discontinuous strand
control of cell division go signals
Critical volume of cell when area of membrane is inadequate for exchange
Chemicals (e.g., growth factors, hormones, cyclins, and cyclin-dependent kinases (Cdks))
control of cell division stop signals
Contact inhibition
Growth-inhibiting factors produced by repressor genes
Protein Synthesis
DNA is the master blueprint for protein synthesis
Gene: Segment of DNA with blueprint for one polypeptide
Triplets of nucleotide bases form genetic library
Each triplet specifies coding for an amino acid
Gene:
Segment of DNA with blueprint for one polypeptide
Messenger RNA (mRNA)
Carries instructions for building a polypeptide, from gene in DNA to ribosomes in cytoplasm
carry codon
Transfer RNAs (tRNAs)
Bind to amino acids and pair with bases of codons of mRNA at ribosome to begin process of protein synthesis
anticodons
Transcription
Transfers DNA gene base sequence to a complementary base sequence of an mRNA
transcription three steps
initiation, elongation, termination
initiation
With the help of transcription factors, RNA polymerase binds to the promoter, pries apart the two DNA strands, and initiates mRNA synthesis at the start point on the template strand
elongation
As the RNA polymerase moves along the template strand, elongating the mRNA transcript one base at a time, it unwinds the DNA double helix before it and rewinds the double helix behind it.
termination
mRNA synthesis ends when the termination signal is reached. RNA polymerase and the completed mRNA transcript are released.
Translation
Converts base sequence of nucleic acids into the amino acid sequence of proteins
codon
Each three-base sequence on DNA is represented by a codon
Codon—complementary three-base sequence on mRNA
translation process
mRNA attaches to a small ribosomal subunit that moves along the mRNA to the start codon
Large ribosomal unit attaches, forming a functional ribosome
Anticodon of a tRNA binds to its complementary codon and adds its amino acid to the forming protein chain
New amino acids are added by other tRNAs as ribosome moves along rRNA, until stop codon is reached
Ubiquitin
(regulatory protein in all tissues) tags damaged or unneeded soluble proteins in cytosol; they are digested by enzymes of proteasomes
Active transport process
Nucleus, to rough ER, vesicle, golgi, vesicle, plasma membrane for exocytosis
Transcription factors
Enzymes and proteins
Loosen histones (help package dna into chromosome)
Binds to promoter
Mediates bonding of RNA polymerase to promoter
Transcription rna polymerase
Unzips and copies dna by itself, stops at termination codon
Only copy one strand with right gene
Only unwound in rna polymerase
Translation process
Mrna attaches to ribosome
Anticodon attaches to codon
Adds amino acids to forming protein
Stops at stop codon
Homeostasis process order
Stimulus Receptor Afferent pathway Control center Efferent pathway Effector Return to balance
Glycoproteins
Recieve signal
Glycolipid
Cell recognition
