Ch1.1-1.2: the Cell - Kaplan MCAT Bio

cell theory fundamentals

1. all living things are composed of cells

2. the cell is the basic functional unit of life

3. cells arise only from preexisting cells

4. cells carry genetic info in the form of DNA. this genetic material is passed on from parent to daughter cell (this one was added later)

viruses

small structures that contain genetic material but are unable to reproduce on their own

• virions can only replicate by invading other organisms

• may contain RNA as their genetic info

• not considered living organisms

eukaryotic cells

contain a true nucleus enclosed in a membrane

• eukaryotic organisms can be unicellular or multicellular

• most organelles are membrane bound

prokaryotic cells

do not contain a nucleus

membranes of eukaryotic cells

• consist of a phospholipid bilayer

• surfaces are hydrophilic

• inner portion is hydrophobic

the membranes of eukaryotic cells have hydrophilic surfaces

electrostatically interacting with the aqueous environments inside and outside the cell

the inner portion of the membranes of eukaryotic cells are hydrophobic

helps to provide a highly selective barrier between the interior of the cell and the external environment

cytosol

each cell has a cell membrane enclosing a semifluid cytosol in which organelles are suspended

• cytosol allows for the diffusion of molecules throughout the cell

organization of genetic material

within the nucleus, genetic material is encoded in DNA, which is organized into chromosomes

eukaryotic cells reproduce by:

mitosis

• allowing for the formation of two identical daughter cells

nucleus

control center of the cell

• contains all genetic material necessary for cell replication

• surrounded by the nuclear membrane or envelope

nuclear membrane or envelope

a double membrane that maintains a nuclear environment separate and distinct from the cytoplasm

nuclear pores

nuclear pores in the nuclear membrane allow for selective two-way exchange of material between the cytoplasm and the nucleus

transcription

formation of hnRNA from DNA, which is subsequently processed to form mRNA

translation

the formation of a peptide from mRNA

genes

genetic material (DNA) contains coding regions called genes

histones

linear DNA is wound around organizing proteins known as histones

chromosomes

linear DNA is wound around histones and then is further wound into linear strands called chromosomes

nucleolus

subsection of the nucleus where rRNA is synthesized

• takes up up to 25% of the total volume of nucleus

• darker spot in nucleus

mitochondria

important metabolic functions

• contains outer and inner membranes

mitochondria outer membrane

serves as a barrier between the cytosol and the inner environment of the mitochondrion

mitochondria inner membrane

• thrown into numerous infoldings called cristae

• contains the molecules and enzymes necessary for the electron transport chain

cristae

highly convoluted structures that increase the surface area available for electron transport chain enzymes

intermembrane space

space between the inner and outer mitochondrial membranes

mitochondrial matrix

the space inside the inner mitochondrial membrane

what does proton pumping from mitochondrial matrix → intermembrane space accomplish?

establishes the proton-motive force

• ultimately these protons flow through ATP synthase to generate ATP during oxidative phosphorylation

mitochondria are semiautonomous

they contain some of their own genes and replicate independently of the nucleus via binary fission

• paradigmatic example of cytoplasmic or extranuclear inheritance

cytoplasmic or extranuclear inheritance

the transmission of genetic material independent of the nucleus

serial endosymbiosis theory

attempts to explain the formation of some of the membrane-bound organelles

• posits that these organelles formed by the engulfing of one prokaryote by another and the establishment of a symbiotic relationship between the two

mitochondria are also capable of killing the cell- how?

by release of enzymes from the electron transport chain

apoptosis

programmed cell death

• the mitochondria’s release of enzymes from the electron transport chain kickstarts apoptosis

lysosomes

membrane-bound structures containing hydrolytic enzymes that are capable of breaking down many different substrates

• including substances ingested by endocytosis and cellular waste products

autolysis

like mitochondria, when lysosomes release their hydrolytic enzymes, it results in apoptosis. in this case, the released enzymes directly lead to the degradation of cellular components

auto = self

lysis = breakdown/destroy

endoplasmic reticulum

a series of interconnected membranes that are contiguous with the nuclear envelope

• smooth and rough ER

• double membrane folded into many invaginations (complex structures in central lumen

rough ER

studded with ribosomes (rough ER = ribosomes)

• protein translation for secretion into lumen

ribosomes in RER

permit the translation of proteins destined for secretion directly into its lumen

smooth ER

lacks ribosomes and is utilized primarily for:

1. lipid synthesis

2. detoxification of certain drugs and poisons

3. transports proteins from RER to Golgi

Golgi apparatus

consists of stacked membrane-bound sacs

• materials from the ER are transferred to the Golgi apparatus in vesicles

• once in Golgi, the cellular products can be modified

once in the Golgi, cellular products can be modified- how?

1. the addition of various groups (carbohydrates, phosphates, sulfates)

2. introduction of signal sequences - which direct the delivery of the product to a specific cellular location

what happens to cellular products after modification and sorting in the Golgi?

repackaged into vesicles

• vesicles are then transferred to the correct cellular location

exocytosis

if a cellular product is destined for secretion, then:

• the secretory vesicle merges with the cell membrane

• its contents are released via exocytosis

cells that require a lot of energy for locomotion (such as sperm cells) have high concentrations of ______

mitochondria

cells involved in secretion (such as pancreatic islet cells and other endocrine tissues) have high concentrations of _____

RER and Golgi apparatus

peroxisomes

• contain hydrogen peroxide

• primary function: break down of very long chain fatty acids via β-oxidation

• participate in synthesis of phosopholipids

• contain some of the enzymes involved in pentose phosphate pathway

cytoskeleton

• provides structure to the cell and helps it to maintain its shape

• provides a conduit for the transport of materials around the cell

components of cytoskeleton

1. microfilaments (actin filaments)

2. microtubules

3. intermediate filaments

microfilaments (actin filaments)

• made up of solid polymerized rods of actin

• organized into bundles and networks

• resistant to compression and fracture → providing protection for the cell

• can use ATP to generate force for movement by interacting with myosin, such as in muscle contraction

cytokinesis

the division of materials between daughter cells

cleavage furrow

during mitosis, the cleavage furrow is formed from microfilaments, which organize as a ring at the site of division between the two new daughter cells

microtubules

hollow polymers of tubulin proteins

• microtubules radiate throughout the cell, providing the primary pathways along which motor proteins like kinesin and dynein carry vesicles

cilia and flagella

motile structures composed of microtubules

• share the same structure, composed of 9 pairs of microtubules forming an outer ring and 2 microtubules in the center

cilia

projections from a cell that are primarily involved in movement of materials along the surface of the cell (such as cilia lining the respiratory tract to move mucus)

flagella

structures involved in movement of the cell itself (such as sperm cells)

9+2 structure

structure shown in cilia and flagella (only seen in eukaryotic organelles of motility)

• 9 pairs of MTs forming an outer ring

• 2 MTs in the center

centrioles

• found in the centrosome

• organizing centers for MTs

• structured as 9 triplets of MTs with a hollow center

• during mitosis, centrioles migrate to opposite poles of the dividing cell and organize the mitotic spindle

kinetochores

complexes where microtubules emanating from the centrioles attach to the chromosomes

• the microtubules can then exert force on the sister chromatids, pulling them apart

intermediate filaments

diverse group of filamentous proteins, including keratin, desmin, vimentin, and lamins

• many IFs are involved in cell-cell adhesion

• many IFs are involved in maintenance of the overall integrity of the cytoskeleton

• IFS can withstand a lot of tension, making cell structure more rigid

• IFs help anchor other organelles (including the nucleus)

types of tissues

1. epithelial tissue

2. connective tissue

3. muscle

4. nervous tissue

epithelial tissues

cover the body and line its cavities

• providing a means for protection against invasion and desiccation

• in certain organs, epithelial cells are involved in absorption, secretion, and sensation

• to remain one cohesive unit, they are tightly joined to each other and to the basement membrane

• highly diverse and serve numerous functions depending on the identity of the organ in which they are found

basement membrane

an underlying layer of connective tissue that anchors epithelial cells

parenchyma

in most organs, epithelial cells constitute the parenchyma:

• the functional parts of the organ

epithelial cells are often polarized, meaning:

• one side faces a lumen or the outside world

• the other side interacts with underlying blood vessels and structural cells

lumen

the hollow inside of an organ or tube

types of epithelia based on # of layers

1. simple

2. stratified

3. pseudostratified

simple epithelia

one layer of cells

stratified epithelia

multiple layers of cells

pseudostratified epithelia

appear to have multiple layers due to differences in cell height BUT in reality are only one layer

types of epithelial cells based on shape

1. cuboidal

2. columnar

3. squamous

cuboidal cells

cube shaped

columnar cells

long and thin

squamous cells

flat and scalelike

connective tissue

supports the body and provides a framework for the epithelial cells to carry out their functions

• main contributors to the stroma

• most cells in connective tissues produce and secrete materials such as collagen and elastin to form the extracellular matrix

stroma

support structure