AP Bio Unit 2 Pt. 1 - Cell Structure and Functions

cells

basic structural and functional units of every organism

all cells contain…

• bound to a plasma membrane

• cytosol/cytoplasm

• chromosomes(how DNA is packaged)

• ribosomes(proteins)

prokaryotic cells

domains: bacteria and archaea(think plankton)

• DNA is in the nucleoid region

• generally smaller in size

eukaryotic cells

protists, fungi, animals, and plants

• DNA is in the nucleus

• contain membrane bound organelles

organelles

membrane bound structures in eukaryotes

endomembrane organelles

• nuclear envelope

• endoplasmic reticulum

• golgi complex

• lysosomes

• vesicles/vacuoles

• plasma membrane

energy organelles

• mitochondria

• chloroplasts

compartmentalization

allows for different metabolic reactions to occur in different locations

• increases surface area for reactions to occur

• prevents interfering reactions from occurring in the same location

• think “separate to specialize”

unique cell components: plants

• chloroplasts

• central vacuole

• cell wall

• plasmodesmata

unique cell components: animals

• lysosomes

• centrosomes

• flagella

nucleus

• contains chromosomes (genetic info)

  • enclosed by the nuclear envelope(double membrane)

• has pores(regulate entry and exit of materials from the cell)

• contains a 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

    • assemble into ribosomes

      • ribosomes translate messages found on mRNA into the primary structure of polypeptides

rRNA

ribosomal RNA

• translates RNA info to amino acids

ribosomes 

• comprised of ribosomal RNA and proteins

  • function: synthesizes proteins

• can be found in two locations:

  • Cytosol: proteins produced here generally function only within the cytosol (i.e., enzymes)

    • known as “free ribosomes”

  • bound to the ER or nuclear envelope

    • proteins produced here can be secreted from the cell

      • leave via transport vesticles

• not bound by a membrane!

Endoplasmic Reticulum (ER)

• a network of membranous sacs and tubes

  • synthesizes membranes

  • compartmentalizes the cell to keep proteins form in the rough ER separate from those of the free ribosomes

• two types: rough and smooth

rough ER

• “creates, packages, and sends”

• contains ribosomes bound to the ER membrane

• think R = ribosomes

smooth ER

• “support”

• contains no ribosomes

• synthesizes lipids, metabolizes carbohydrates, and detoxifies the cell

golgi complex

• Amazon basically

• “modifies/repackages”

• contains flattened membranous sacs called cisternae

• separate the sacs from the cytosol

• each cisternae is not connected

• has directionality

• receives transport vesicles with materials from the ER

  • modifies the materials(ensures newly formed proteins are folded correctly or modified correctly)

  • sorts the materials

  • adds molecular tags

  • packages materials into new transport vesicles that exit the membrane via exocytosis

cis face

front of golgi complex

• receives vesicles from the ER

trans face

in golgi complex

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

Lysosomes

• “break” —> hydrolysis

• “waste management”

• membranous sac with hydrolytic enzymes

• hydrolyzes macromolecules in animal cells

• autophagy

autophagy

lysosomes can recycle their own cell’s organix materials

• allows the cell to renew itself

peroxisomes

• sub-type of lysosomes

• membrane bound metabollic compartment

  • catalyze reactions that produce H2O2 (hydrogen peroxide)

    • enzymes in peroxisomes then break down H2O2 to water and oxygen

vacuoles

• large vesicles that stem from the ER and Golgi

  • selective in transport

types of vacuoles

food: form via phagocytosis and then are digested by lysosomes

contractile: maintain water levels in cells

central: found in plants

• contain inorganic ions and water

• important for turgor pressure

autophagy 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 m’cules are released back into the cytoplasm)

steps in protein synthesis

1. transcription and RNA processing

• occurs in the nucleus; the DNA sequence of a gene is copied into mRNA which serves as a template that will be used to assemble the protein; after transcription, the mRNA undergoes processing ot prepare for translation; processed mRNA exits via nuclear pores

2. translation

• mRNA is then translated by ribosomes; if the mRNA codes for proteins meant for secretion, insertion into the cell membrane, or lysosomes, is translated by ribosomes bound to the rough ER and will be sent to the golgi; if mRNA codes for proteins that will function in the cytosol, it is translated by free ribosomes in the cytoplasm and dischagred from there; afterwards, the polypeptide cahin begins to fold intoa  specific three-dimensional shape; the rouhg ER then packages the protein into vesicles

3. Folding and Modification

• the vesicles that bud off from the Rough ER travel to the cis face of the golgi complex, where the protein will undergo further modifications, such as the addition of sugar groups or cleavage of the polypeptide chain; these proteins are then packaged into vesicles that bud off from the trans face

4. Secretion or Use in the Cell

• the vesicles containing the modififed proteins can either fuse with the plasma membrane to secrete the proteins outside thecell via exocytosis or deliver them to specific locations within the cell where they are needed

translation

process where ribosomes read the mRNA sequence and translate it into a polypeptide chain (sequence of amino acids)

what reduces protein levels?

diseases

Endosymbiont Theory

the theory that explains the similarities mitochondria and chloroplasts have to a prokaryote

• states that an early eukaryotic cell engulfed a prokaryotic cell

  • pro-cell became an endosymbiont (cell that lives in another cell)

    • became one functional organism

• explains compartmentalization

evidence of the endosymbiont theory

1. double membranes

2. ribosomes

3. circular DNA

4. capability of functioning on their own

the endosymbiont theory applies to which organelles?

energy organelles!

mitochondria

in all eu-cells

site of cellular respiration

• “batteries of the cell” — powers cell and works independently

  • structure of the double membrane: outer membrane is smooth, inner membrane has folds called cristae

    • divides mitochondria into two internal compartments and increases surface area

    • intermembrane: space between inner and outer membrane

    • mitochondrial matrix: enclosed by inner membrane

    • location for Krebs cycle

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

• number of in a cell correlates with metabolic activity

  • cells with high metabolic activity have more

    • ex: cells that move/contract (muscle cells)

chloroplasts

“factory”

specialized organelles in photosynthetic organisms

• site of photosynthesis

• contains the green pigment chlorophyll

• inside of double membrane:

  • thlyakoids (grana)

  • stroma

thylakoids

in double membrane of chloroplasts; membranous sacs that can organize into stacks called grana (where light dependent reactions occur)

stroma

fluid around thlyakoids int he double membrane of a chloroplast

• location of calvin cycle

• contains: chloroplast DNA, ribosomes, and enzymes

cytoskeleton

network of fibers throughout the cytoplasm

• give structural support (esp animal cells) and mechanical support:

  • anchors 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

1. microtubules

2. microfilaments

3. intermediate filaments

microtubules

hollow, rod-like structures made of the protein tubulin

• grow from the centrosome

  • assist in _______ assembly

• functions: serves as the structural support (think of tracks) for the movement of organelles that are interacting with motor proteins; assists in the separation of chromosomes during cell division; cell motility (internal movement—like cilia and flagella)

microfilaments

thin, solid rods made of the protein actin

• functions: Maintains cell shape (bear tension), assists in muscle contraction and cell motility(actin works with another protein called myosin to cause a contraction); division of cells (contractile ring of the cleavage furrow)

intermediate filaments

fibrous proteins made up of varying subunits

• permanent structural elements of cells

• functions: maintain cell shape, anchor nucleus and organelles, forms the nuclear lamina (lines the nuclear envelope)

cellular metabolism depends on…

…cell size

• cellular waste must leave

• dissipate thermal energy

• nutrients and other resources/chemical rxns must enter

at a certain size, what happens to a cell?

it becomes too difficult to regulate what comes in and what goes out of the plasma membrane 

what dictates the function of a cell?

the size

cells need a ___ surface area-to-volume ration to ____ the exchange of material through the plasma membrane

high; optimize ; SA: V=SA/V

cells tend to be…

…small

small cells have a ___ SA:V ratio

high

• optimizes the exchange of materials at he plasma membrane

large cells have a ___ SA:V ratio

low

• lose efficiency exchanging materials

  • cellular demand for resources increases

  • rate of heat exchange decreases