MIDTERM 2 (TOPIC 6)

Plasma membrane (cell membrane)

found in prokaryotic/eukaryotic cells & separates the interior of a cell from its external environment

• consists of a lipid bilayer that is semipermeable

• regulates the transport of materials entering/exiting the cell

Cytosol

the fluid portion of the cytoplasm, excluding the organelles & other membrane-bound structures within a cell

Cytoplasm

semifluid substance of a cell between the plasma membrane & nuclear envelope

• includes all the contents within the cell membrane excluding the nucleus

Prokaryote

organisms whose cells lack internal membranes (nucleus +other organelles)

• DNA is concentrated in the nucleoid

• include Bacteria

• small : around 1-5μm across

Eukaryote

there are other membrane- bound organelles that subdivide cellular functions

• DNA is found in the nucleus

• include plants, animals, protists, fungi

• around 10-100μm diameter can be larger

Nucleoid

region within a prokaryotic cell where the genetic material (DNA) is located

• not enclosed by a membrane

• Single, circular DNA molecule

• Not easily visible

Nucleus

found in eukaryotic cells, serving as the cell's control center

• Enclosed by a double membrane (nuclear envelope)

• Linear Chromosomes

• Visible under microscope

Organelle

a sub-cellular structure that has one or more specific jobs to perform in the cell

(like an organ in the body)

• membrane-bound

• but non-membrane-bound also exist

ex : nucleus, mitochondria, vesicles

Nuclear lamina

array of intermediate filaments in the inner surface of the nuclear envelope

• maintains the shape of the nucleus

• composed of lamins

• only in eukaryotic cells

Nuclear envelope

double membrane (two lipid bilayers) that encloses the nucleus in eukaryotic cells, separating (DNA) from the cytoplasm

• acts as a barrier

• aka nuclear membrane

• 2 lipid bilayers : outer/inner

Nuclear pore

large protein complex (pore complex), in the nuclear envelope

forms a channel that regulates the selective exchange of molecules between the nucleus & the cytoplasm

• acts as a gatekeeper, allowing RNA/ proteins, to pass but restricting others

• Composed of nucleoporins

Chromosome

threadlike structures made of protein & a single molecule of DNA that serve

carry the genomic information from cell to cell & ensure accurate distribution of DNA during cell division

• Humans : 46 chromosomes = 23 pairs

RIbosome

responsible for carrying out the process of translation (mRNA into proteins)

consist of different Protein/ (rRNA) which assemble into separate large/ small subunits

• can be free in the cytosol or bound to the cytosolic face of the endoplasmic reticulum (ER)

• found in ALL cells

Endoplasmic reticulum (ER)

a membrane system continuous w/ the nuclear envelope & is found near the nucleus

• divided into rough ER (w/ ribosomes) & smooth ER (w/o ribosomes)

• involved in protein/ lipid synthesis

Smooth ER

(ER) a network of membranous tubules in the cytoplasm of eukaryotic cells that’s not bound to ribosomes

carries out metabolic functions :

• synthesis of lipids (steroid hormones, oils, phospholipids)

• metabolism of carbohydrates

• stores ions (like Ca++) so they’ll be released in a burst to trigger other events

Rough ER

(ER) a network of membranous tubules in the cytoplasm of eukaryotic cells that is bound to ribosomes

• where proteins that’ll be secreted are made

• where integral membrane proteins/ membranes, are made

Transport vesicle

small, membrane-bound sac in eukaryotic cells that move molecules, like proteins/ lipids, between different parts within the cell

• act as miniature transport vehicles

• (ER) to Golgi apparatus

• Golgi to plasma membrane

Golgi apparatus : packaging center

system of membranes in eukaryotic cells that processes &packages Proteins/ Lipids, many destined for secretion/transport to other cellular compartments

• ribosomes don’t interact w/ it

• not continuous w/ ER/ Nuclear membrane

• have flattened membrane sacs (cisternae)

• Cis face: entry side, nucleus side (receives vesicles from the ER)

• Trans face: exit side, plasma membrane side (ships out processed products in vesicles)

Insulin

A secreted protein/ peptide hormone w/ quaternary structure that’s the product of the human INS gene

It circulates in bloodstream & binds to insulin receptors on the surface of cells

The cells move glucose transporter channel proteins to the membrane, allowing glucose to enter by facilitated diffusion

• synthesized in pancreatic islet cells which occurs on the rough ER

Cisternae

flattened membrane-bound sacs found within the (ER) & Golgi apparatus of eukaryotic cells

• ER: involved in synthesis (rough ER) & lipid metabolism (smooth ER)

• Golgi apparatus: serve as compartments for modification, sorting, packaging of proteins/ lipids

Lysosome : "garbage disposal”

membrane-bound vesicle in eukaryotic cells that contains digestive enzymes

break down & recycles :

• cellular waste, damaged organelles, & invading pathogens (viruses/bacteria)

Peroxisome

single-membrane-bound organelle in eukaryotic cells involved in lipid metabolism & detoxification

• Has enzymes in a "crystalloid core"

• Not part of the endomembrane system

• detoxifies alcohols & digests fatty acids

Enzymes transfer hydrogens from molecules to oxygen producing (peroxide)

• diseases to it = lipid accumulation & nervous system + tissue issues

Hydrolase

a class of hydrolytic enzymes used as biochemical catalysts to digests macromolecules & break a chemical bond

uses water to break down large molecules into smaller ones :

• (protein, lipids, nucleic acids, carbohydrates, fat molecules)

Autophagy : "self-eating"

cellular process where a cell digests & recycles its own components/ materials

• removes damaged or dysfunctional components, & provides building blocks (amino acids/ lipids) for new cellular structures

Vacuole

membrane-bound sacs found in the cytoplasm of cells used for storage, digestion, & regulation of internal conditions

• Plants/ Fungi : digestive vacuoles like animal lysosomes

• Protists : a contractile vacuole that stores water/salts (crucial in osmotic balance)

Central vacuole

large, fluid-filled organelle that stores water, enzymes, & waste products

• contains cell sap, which has potassium/ chloride ions

• can absorb water & contribute to regulation of cell size

• crucial role in maintaining turgor pressure, which provides structural support, (can occupy 90% of cell's volume)

Mitochondria : "powerhouse" of the cell

membrane-bound cell organelles found in nearly all eukaryotic cells, responsible for generating most of the cell's chem energy, (in form of ATP)

converts energy from one form to another : (glucose, fatty acids) to ATP

• has an Inner & Outer membrane

• extensive tube-like network

Matrix

material (tissue) in between a eukaryotic organism's cells,

• the space in the inner part of mitochondria

• surrounds & supports cells, acting as a structural framework

• Contains enzymes, mitochondrial DNA, & ribosomes

Intermembrane space : (IMS)

space between the inner & outer membranes of mitochondria & chloroplasts

• key role in cellular respiration

• (H⁺) are pumped into IMS during the ETC

Chloroplast

a specialized organelle found in Plants/ Algae, responsible for photosynthesis

uses energy from sunlight to convert CO2 + H2O into sugars & other organic compounds

• Chlorophyll (absorbs light energy) is found in the chloroplasts & gives plants green color

• inside is a system of thylakoids

• ‘dynamic’ structures (change shape over time)

Thylakoid

a system of stacked membranous discs inside chloroplastsin (plants/ algae) & cyanobacteria

key for photosynthesis, (has chlorophyll & other light-absorbing pigments)

• site where light-dependent reactions of photosynthesis occur (generation of ATP & NADPH)

• Thylakoids are often stacked into structures called grana

Grana

stacks of disk-shaped structures called thylakoids within chloroplasts of plant cells

• crucial for photosynthesis (light-dependent reactions) bc they have chlorophyll etc.

• involved in generating ATP & NADPH

• thylakoids stacked like coins

Endosymbiosis

biological relationship where one organism lives inside another, to the benefit of both

• Basis of the endosymbiotic theory, (origin of mitochondria & chloroplasts)

Cytoskeleton

Dynamic network of protein filaments/ tubules within the cytoplasm of eukaryotic cells that supports the cell’s structure & enables movement

• maintains & changes the cell’s shape

• provides a scaffold for motor proteins to move structures (like vesicles)

• helps produce cellular motion

3 types of protein fibers that all function in maintenance of cell shape :

Microtubules, Microfilaments, Intermediate filament

Microtubule

Cylindrical polymers made of α- & β-tubulin dimers; one main component of cytoskeleton

(25 nm diameter)

Facilitate chromosome movements during mitosis & meiosis

• Motor proteins are capable of walking along microtubules in an ATP-dependent manner

• give flagella (e.g. in sperm) or cilia (e.g. in lung tissue) their ability to move

Microfilament

Thin, flexible protein filaments made of two intertwined strands of actin polymers

(7 nm)

Have polarity (crucial for directional movement)

function in changes in cell shape:

• formation of pseudopods (cell projections)

• forming of the cleavage furrow during cytokinesis

Intermediate filaments

Cytoskeletal filaments made of fibrous proteins (keratin, lamins, vimentin), providing mechanical support to cells

(8-12 nm)

No polarity

• anchor the nucleus & other organelles in place

• form part of the nuclear lamina (mesh-like layer that supports the nuclear envelope)

• Provide tensile strength, helping cells resist mechanical stress