2.1 Cell Structure and Function, 2.9 Cell Compartmentalization

Ribosomes

compromised of ribosomal RNA and protein

non-membrane

found in cells in all forms of life and reflect the common ancestry in all known life

function is to synthesize proteins (translate messages found on mRNA into primary structure of polypeptides)

can be found in the cytosol or bound to the ER or nuclear envelope

if found in the cytosol, proteins produced there generally function only within the cytosol(ex. enzymes), known as “free ribosomes”

if found bounded to ER or nuclear envelope, proteins produced there can be secreted from the cell and leave via transport vesicles

Compartmentalization

eukaryotic membranes and membrane-bound organelles allow for compartmentalization(different metabolic processes and enzymatic reactions occur in different locations)

increases surface area for reactions to occur

prevents interfering reactions from occurring in the same location

even though prokaryotes lack membrane bound organelles and don’t have compartmentalization, prokaryotes can have internal regions with specialized structuctures and functions ex. proteins involved in motility and cell division can be localized to carry out their specific function

Endomembrane system

Organelles and subcellular components that interact (directly or via vesicles) to modify, package, and transport polysaccharides, proteins, and lipids in the cell

1. Nuclear envelope

2. Endoplasmic reticulum (ER)

3. Golgi complex

4. Lysosomes

5. Transport vesicles/vacuoles

6. Plasma membrane

(not a specific order for everything just all the organelles involved)

Nuclear envelope

surrounds the nucleus

double membrane

has pores that regulate entry and exit of materials from the cell

continuous with the ER membrane

contains a nucleolus(in the nucleus)

Nucleus

contains genetic material

contains the nucleolus

Nucleolus

dense region of the nucleus where ribosomal RNA (rRNA) is synthesized

rRNA is combined with proteins to form large and small subunits of ribosomes

subunits exit via nuclear pores and assemble into ribosomes

Endoplasmic reticulum (ER)

a network of membranous sacs (cisternae) and tubules

function is the provide mechanical support by helping cells maintain shape and intracellular transport

2 types: Rough and smooth

Rough ER

contains ribosomes bound to the ER membrane

compartmentalizes protein synthesis

folds and modifies newly synthesized proteins

Smooth ER

contains no ribosomes

synthesizes lipids and detoxifies the cell

Golgi Complex

contains flattened membranous sacs called cisternae

separate the sacs from the cytosol

has directionality

cis face receives vesicles from the ER

trans face sends vesicles back out into the cytosol to other locations or to the plasma membrane for secretion

function is to receive transport vesicles with materials from the ER, modify the materials(correctly fold and chemically modify newly formed cellular products like proteins), sorts the materials, adds molecular tags, and packages materials into new transport vesicles that exit the membrane via exocytosis

Plasma membrane

separates internal cell environment from external environment

selectively permeable(regulars what materials can enter and exit)

proteins are embedded in the cell here or secreted outside the cell via exocytosis

Lysosomes

membranous sac with hydrolytic enzymes in animal cells

only in animal cells

function is to hydrolyze (digest/break down) macromolecules and autophagy

plays a role in apoptosis (programmed cell death)-membrane becomes permeable—>releases enzymes into cytoplasm→breaks down cellular components

Autophagy

lysosomes can recycle their own cell’s organix materials and organelles that are not functioning properly

allows the cell to renew itself

steps:

1. a membrane forms around the cellular component targeted for degradation

2. membrane engulfs cellular components(forming a structure called an autophagosome)

3. fuses with lysosome

4. hydrolytic enzymes in lysosome digest the organelles and their components are recycled(amino acids and other small molecules are released back into the cytoplasm)

Vesicles

a small, membrane-bound sac within a cell that functions to transport, store, or digest cellular substances, such as proteins and lipids

crucial for moving materials within a cell and interacting with other cells by playing key roles in endocytosis, exocytosis, and intracellular transport between organelles like the endoplasmic reticulum and the Golgi apparatus

Vacuoles

vesicles that stem from the ER and the Golgi

selective in transport

in animal cells they are small in size;more per cell, assist in endocytosis/exocytosis processes, and store cellular materials

in plant cells there is a central vacuole;large in size, stores nutrients and water;important for turgor pressure(applies pressure on the cell wall with water to maintain structure), can function like lysosomes

Peroxisomes

membrane bound metabolic compartment

not a part of the endomembrane system

catalyze reactions that produce H2O2(hydrogen peroxide)

H2O2 can detoxify certain compounds, but can damage the cell if any escapes, so enzymes in peroxisomes (catalase) then break down H2O2 to water and oxygen

function is to break down fatty acid molecules, synthesize certain phospholipids, and detoxify compounds

Mitochondria

energy organelle

site of cellular respiration(produces ATP)

structure of the double membrane:

outer membrane is smooth, inner membrane is highly convoluted(meaning it has many folds);these folds are called cristae

cristae divide the mitochondria into two internal compartments, intermembrane and mitochondrial matrix, and increases the surface area

the intermembrane is the space between the inner and outer membrane

the number of mitochondria in a cell correlates with metabolic activity

cells with high metabolic activity have more mitochondria ex. cells that move and contract

Mitochondrial matrix

enclosed by inner membrane

location for the Krebs cycle

contains enzymes that catalyze cellular respiration and produce ATP, mitochondrial DNA, and ribosomes

Chloroplast

energy organelle

specialized organelles in plants and photosynthetic algae

site of photosynthesis

contains the green pigment chlorophyll

inside of its double membrane are thylakoids and stroma

Thylakoids

membranous sacs that can organize into stacks called grana

light dependent reactions occur in grana

Stroma

fluid around thylakoids

location for the calvin cycle

contains chloroplast DNA, ribosomes, and enzymes

Cytoskeleton

a network of fibers throughout the cytoplasm

give structural support(especially for animal cells) and mechanical support using anchor organelles

-allows for movement of vesicles and organelles and/or the whole cell(movement occurs when the cytoskeleton interacts with motor proteins)

3 types of fibers in the cytoskeleton are microtubules, microfilaments, and intermediate filaments

Microtubules

thickest filament in the cytoskeleton

in animal cells they grow from the centrosome

function is to serve as structural support(think tracks) for the movement of organelles that are interacting with motor proteins, assist in the movement of chromosomes during cell division, and cell motility (ex. cilia and flagella)

Microfilaments

thin, solid rods made of the protein actin

function is to maintain cell shape by bearing tension, assist in muscle contraction and cell motility (actin works with another protein called myosin to cause a contraction), division of animal cells(contractile ring of the cleavage furrow)

Intermediate Filaments

fibrous proteins made up of varying subunits 

permanent structural elements of cells

function is to maintain cell shape, anchor nucleus and organelles, form the nuclear lamina(lines the nuclear envelope)