Module 2.1: Cell structure, function, and transport

membrane proteins

receptors, enzymes, cell-cell recognition, cell-cell joining, attachment sites, transport molecules

cell-cell joining

intercellular junctions → adhere to one another; communication

types of junctions

tight, desmosomes, gap

tight junctions

integral membrane proteins; impermeable → prevent fluids and molecules from passing

desmosomes

uses Cadherins to interlock like a zipper → prevent cells from tearing apart

hemidesmosomes

desmosomes that link cell to basal lamina → tissue doesn’t float away from site

gap junctions

small tunnels formed by connexons → small molecules can pass through one cell to another

anchorage dependence

surface proteins linking cells together; if lost = apoptosis

resting membrane

more Na in extracellular, more K intracellular

passive membrane transport

no energy needed → due to kinetic properties

results in high to low movement

types of passive transport

simple diffusion, facilitated diffusion, osmosis

simple diffusion

substance diffuses directly through membrane

simple diffusion determined by

extent of concentration gradient, molecular size, temp

substances that can simple diffuse

O2, CO2, steroid hormones, fatty acids, small amount of water

facilitated diffusion

membrane protein assists in transport

carrier proteins

bind to substance → conformational change → carried across membrane

channel protein

facilitated diffusion; when open → substance passes through

types of channels

leaky (always open) + gated

osmosis

movement of water in selectively permeable membrane

due to difference in solute

tonicity

ability of solution to change shape/plasma membrane tension by affecting internal water volume

isotonic solution

osmolarity inside and outside cell is the same

hypertonic solution

osmolarity is higher inside the cell = water flows out, cell shrink

hypotonic solution

osmolarity is lower inside cell = water flows in; cell grows

active membrane transport

ATP needed to move stuff across membrane

primary active transport

direct use of ATP

secondary active transport

ions move across by primary transport → energy stored and is then used by secondary transport

vesicular transport

moves substances that are too large for membrane

transcytosis

moves into then out of cell

vesicular trafficking

moves from one area of a cell to another inside the same cell

exocytosis

transport out of cells

endocytosis

transport into cell

phagocytosis

projections on membrane engulf particle = phagosome

pinocytosis

cell drinking; non specific

plasma membrane folds in on itself; brings in fluid and solutes

establishing ion in membrane potential

K and Na

K diffuses out of cell through leakage channel → brought back through electrical gradient

Na diffuses in bcz of negative environment

Na/K pump

brings 3 Na out and 2 K in

how does Na/K pump maintain RMB

rate of Na out = rate Na diffusion in

nuclear envelope

double membrane enclosing nucleoplasm; outer continuous with ER and inner layer maintains shape

nuclear pores allow stuff to pass in and out

nucleoli

dark staining center of nucleus; involved in synthesis of ribosomal RNA

chromatin consists of

30% DNA

60% histone proteins

10% RNA chains forming or are newly formed

nucleosomes

DNA wrapped around proteins (histones)

chromosmes are

condensed chromatin → protect fragile strands

transcriptions

mRNA = copy of DNA template strand

mRNA transferred out of nucleus to cytoplasm and ribosome for translation

mRNA synthesis

DNA wrapped by histones becomes unwrapped = allows for transcription

transcription regulators bind to DNA and begins mRNA synthesis

translation

mRNA is translated by rRNA to make polypeptide chain

tRNA anticodon binds to mRNA codon

posttranslational modification

forming polypeptide can enter rough ER → sugar groups can be added or shape is altered