Exam 2 of Cell Bio (ch 11, 12,15,9)

Cell membrane is

semi-permeable, forms selective barriers, and allows cells to maintain their own aqueous environment

Do both eukaryotes and prokaryotes have cell membranes?

YESSSS

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Eukaryotes have INTERNAL membranes as well though

What is the cell membrane made of?

Phospholipid bilayer and proteins

Phosphatidylcholine

common phospholipid in membrane; amiphatic

Unsaturated phospholipids

KINKY = more fluid (less packed)

Saturated phospholipids

Straight = less fluid (packed/rigid af)

Purpose of phospholipid bilayers in the membrane

form stable compartments (polar on outside, nonpolar on inside)

Allows for membrane fluidity

Forms a CLOSED system of the cell

Cholesterol

major component of membranes; rigid ring REDUCES membrane flexibility/fluidity

Organelle membranes have 2 sides:

cytosolic (outside) and internal side (lumen)

Transporter proteins

move phospholipids around in membranes

Membrane assembly in ER

Phospholipid synthesis adds to cytosolic side of bilayer (UNEVEN)

Scramblase transfers phospholipids RANDOMLY to make growth even

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Bilayer growth is SYMMETRIC

Membrane addition in golgi

NOT random

Phospholipid compositions are different on lumen side vs cytosolic side (distinct sides)

Flippase causes bilayer to be ASYMMETRIC

Functions of membrane proteins

receive information

Import and export small molecules

Movement and expansion

Types of membrane proteins

Transporters/channels

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Anchors (adhere cell)

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Receptors

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Enzymes

Membrane proteins associate differently with membrane due to

amino acid side chains

Types of membrane protein associations

Transmembrane (span membrane)

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Monolayer-associated (attach to 1 side of membrane)

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Lipid Linked (linked to membrane via lipids)

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Protein attached (proteins anchor proteins to membrane)

Transmembrane proteins

typically form a pore (hydrophobic on outside facing bilayer and hydrophilic on inside to make a tunnel for molecules to come into cell)

protein stabilization in lipid bilayer is due to

protein-protein interactions:

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\-Cell cortex barriers

\-cell to cell adhesion

\-extracellular matrix

\-diffusion (tight junctions)

proteins can be regionally restricted by

tight junctions

tight junctions

pinch and hold cell to restrict protein movement

eukaryotic cells have membrane modifications (carbohydrate) that aid in

cell signaling

cell recognition

cell to cell association

Types of membranes in cells

Bilayer (cell membrane) or intracellular membranes

Solutes cross membrane based on

size, charge, and solubility

Na+ and Cl- are higher (inside/outside) cell?

OUTSIDE

K+ and anions are higher (inside/outside) cell?

INSIDE

Small nonpolar molecules (hormones, O2, steroids) pass through membrane

easily

Small uncharged polar molecules (H2O) pass through membrane

fairly easily

Larger uncharged polar molecules (amino acids, nucleotides) pass through membrane

not easily

Ions pass through membrane

not easily- usually require help

Simple diffusion

movement of solutes from high conc → low conc (no energy)

channels

movement of solutes from high conc → low conc (no energy- passive trasnport)

transporters

movement of solutes from high conc → low conc (no energy-passive transport )

Pumps

movement of solutes from low conc → high conc (energy- ACTIVE transport)

Inside of cell is (neg/pos)?

NEGATIVE

Outside of cell is (neg/pos)?

POSITIVE

Sodium/Potassium pump

requires energy; pumps 3 Na+ out of cell and 2 K+ in to cell

Ouabain

inhibits Na/K pump by preventing K+ from binding

Symport

moves molecules in same direction (glucose-Na)

antiport

moves molecules in different directions (Na/K pump)

Uniport

moves 1 solute down its concentration gradient

Glucose-Na+ symport

moves Na+ and glucose into cell

Purpose of membrane bound organelles in eukaryotes

\-establish compartments within cell

\-compartments allow for specialized functions

Double membrane organelles in eukaryotes

nucleus, mitochondria,

How might nucleus double membrane have formed?

Protein sorting purpose

proteins are transported to their appropriate location(s)

Types of protein sorting

nuclear, across membranes, vesicles

Nuclear sorting

requires energy; protein remains folded

Across membrane sorting

requires energy; protein is unfolded

vesicles sorting

requires energy; protein remains folded

\-pass through nuclear pore

Purpose of signal sequences

determine where protein is transported to

no signal sequence

protein stays in cytosol

is signal sequence removed at end?

yes- once protein reaches final destination

Protein translocators

transport proteins across membranes

Nuclear pore structure

have disordered regions that form a mesh

\-large molecules cannot pass easily, but small molecules can

\-large molecules require receptors and energy (GTP) to cross

Nuclear localization signal

directs protein from cytosol to nucleus (signal sequence)

How receptors work in nuclear pore

receptors bind target protein

protein links to nuclear pore fibrils

protein crosses pore

How do proteins enter mitochondria?

series of recognition interactions:

\-signal sequence on protein binds to receptor on mitochondria surface

\-protein translocator helps protein cross outer membrane (protein is unfolded)

\-protein translocator helps protein cross inner membrane (unfolded)

\-cleave signal sequence

\-chaperone proteins help protein refold

How do proteins enter ER?

\-Signal recognition proteins (SRP) bind to ribosome/ER complex

\-SRP receptor recognizes SRPs

\-translocator proteins bring protein(s) into ER

\-Translation occurs in ER

\-Transfer polypeptide across bilayer

How do vesicles work?

They have phospholipid bilayers, so they can FUSE with plasma membranes on either side

Endocytosis

bring things in

Exocytosis

take things out

How can proteins be modified in ER?

Sugar monomers add to amino acid of protein

\-aid in recognition, protection, and/or holding

What happens if a protein is misfolded?

try to fix it or degrade it

Purpose of golgi?

final modifications to proteins and ship proteins off to their location(s)

Two main exocytosis pathways in golgi

constitutive secretion and regulated secretion

constitutive secretion

UNREGULATED exocytosis; always happening

regulated secretion

REGULATED exocytosis; needs a signal in order for exocytosis to begin

Endocytic

plasma membrane pinches inside

Endomembrane system

package, label, and ship proteins; ER, Golgi, peroxisomes, lysosomes, endosomes

Endosomes have 3 pathways

recycling, degradation, and transcytosis

recycling

early endosomes return to membrane

degradation

endosomes travel to lysosome to be degraded

transcytosis

endosomes move to other area of membrane

Endocytic pathways (do/do not) require receptor mediation

DO

Purpose of lysosomes

degrade material via enzymatic digestion

\-acidic (high H conc) due to H+ pump

What happens to degraded materials?

transported out to cytosol

3 ways lysosomes receive content

phagocytosis, endocytosis, and autophagy

phagocytosis

eating

autophagy

old organelles are sent to lysosome and recycled back to cell (recycles parts of self)

Ways that genetic variation is generated?

Mutation within gene

Mutation in regulatory DNA

Gene duplication and divergence

Exon Shuffling

Transposition

Exon shuffling

moving exons around within 2 different genes \`

transposition

move portion of gene and insert it into new gene

mutations can be

neutral

beneficial

harmful

horizontal transfer

lateral gene transfer between organisms

germ line cell

gametes

heritable mutations are exchanged via

germ-line cells

transposon

chromosomal segment that can undergo transposition

transposase enzyme

enzyme that binds to transposon to catalyze its movement to another part of genome

\~50% of human genome

mobile gene elements

effects of exon rearrangement during transposition?

impacts coding for proteins and gene expression

two major retrotransposon groups in humans

L1 elements and Alu sequences

Similarities in retrotransposon groups

have RNA intermediate

reverse transcriptase

RNA → DNA

what do transposons and retrotransposons have in common with viruses?

Overtake cell machinery to make copies

Can have DNA or RNA genomes

Can impact eukaryotes and prokaryotes

Retrovirus

RNA virus that utilizes reverse transcriptase

Exons

stay

Introns

spliced out

Receptor for SARS-CoV-2

ACE2

Primary entry points for COVID19

endosomal or cell surface

Glycocalyx

physical barrier around cell; protects cell by preventing viruses from binding to it