Chapter 3: The Cellular Level of Organization

cell membrane

aka plasma membrane; surrounds all animal cells; an extremely pliable structure composed of a phospholipid bilayer, cholesterol, and various proteins; provides a protective layer around the cell and regulates which materials can pass in or out

what function(s) does the cell membrane serve?

provides a protective layer around the cell; regulates which materials can pass in or out

phospholipids are amphipathic molecules, meaning they:

contain both a hydrophobic and hydrophilic region

intracellular fluid (ICF)

the fluid interior of the cell

extracellular fluid (ECF)

the fluid environment outside the cell membrane

interstitial fluid (IF)

extracellular fluid not contained within blood vessels

integral protein

a protein that is embedded within the cell membrane

channel protein

an integral protein that selectively allows particular materials to pass into or out of the cell

recognition protein

marks a cells identity so it can be recognized by other cells

receptor

a type of recognition protein that selectively binds to a specific protein outside the cell, which induces a chemical reaction inside the cell

ligand

the specific molecule that binds to and activates a receptor

glycoproteins

have carbohydrate molecules attached which extend into the extracellular matrix and aid in cell recognition

glycocalyx

a fuzzy-appearing coating that surrounds the cell membrane

true or false: the glycocalyces found in a person’s body are products of that person’s genetic makeup.

true

peripheral proteins

membrane-associated protein that does not span the width of the lipid bilayer, but is attached peripherally to integral proteins, membrane lipids, or other components of the membrane; perform specific functions for the cell

the cell membrane is selectively permeable, meaning that it:

only allows substances that meet certain criteria to pass through unaided

what kind of substances can move easily through the lipid bilayer?

relatively small, nonpolar

water-soluble materials need help crossing the membrane because they:

are repelled by the hydrophobic tails

passive transport

the movement of substances across the membrane without the expidenture of cellular energy

what are the four types of passive transport?

simple diffusion, facilitated diffusion, filtration, osmosis

concentration gradient

the difference in concentration of a substance across a space

diffusion

the movement of particles from an area of higher concentration to an area of lower concentration

simple diffusion

the mechanism of molecules moving across a cell membrane from the side where they are more concentrated to the side where they are less concentrated

facilitated diffusion

the diffusion process for substances that can’t cross the lipid layer due to size, charge, and/or polarity

what agents facilitate the diffusion of substances across the membrane?

channel proteins, carrier proteins

how are carrier proteins different from channel proteins?

carrier proteins are more selective, usually allowing only one particular type of molecule to cross

true or false: water cannot move across the cell membrane without the assistance of channel proteins

false, water can move freely across the cell membrane of all cells

osmosis

the diffusion of water molecules down their concentration gradient through a semipermeable membrane

when and why does osmosis occur?

when there is an imbalance of solutes inside vs outside a cell, water will equalize its own concentration by diffusing to the side with less water/a higher concentration of solute

isotonic

equal tension; same concentration of solutes

hypertonic

higher concentration of solutes

hypotonic

lower concentration of solutes

what happens to cells in a hypotonic solution?

they take on too much water and swell, at risk of eventually bursting

filtration

uses a hydrostatic pressure gradient that pushes fluid and the solutes within it from a higher pressure to a lower pressure area

active transport

the movement of substances across the membrane using energy from adenosine triphosphate (ATP)

adenosine triphosphate (ATP)

a chemical compound utilized by every cell in the body to store and release energy

true or false: active transport usually moves substances down the concentration gradient

false; during active transport, substances are usually being moved up or against the concentration gradient

secondary active transport

when active transport powers the transport of another substance across the membrane

symporters

secondary active transporters that move two substances in the same direction

antiporters

secondary active transport systems that move substances in opposite directions

electrical gradient

a difference in electrical charge across a space

which forms of active transport do NOT require the assistance of membrane carriers?

endocytosis, exocytosis

endocytosis

bringing into the cell; import of material into the cell by formation of a membrane-bound vesicle

exocytosis

taking out of the cell; export of a substance out of a cell by formation of a membrane-bound vesicle

phagocytosis

“cell eating”; the endocytosis of large particles

pinocytosis

“cell drinking”; brings fluid containing dissolved substances into a cell through membrane vesicles

receptor-mediated endocytosis

endocytosis by a portion of the cell membrane that contains many receptors for a specific substance

true or false: exocytosis is basically endocytosis in reverse

true

cytoplasm

internal material between the cell membrane and nucleus of a cell, mainly consisting of a water-based fluid called cytosol, within which are all the other organelles and cellular solute and suspended materials

cytosol

clear, semi-fluid medium of the cytoplasm, made mostly of water

organelles

“little organs”; one of several different types of bodies enclosed in the cellular membrane, each performing a unique function

nucleus

a cell’s central organelle; contains the cell’s DNA

endoplasmic reticulum (ER)

a system of interconnected channels continuous with the nuclear membrane used for transporting, synthesizing, and storing materials throughout the cell

what is the difference between rough ER and smooth ER?

rough ER is dotted with ribosomes, giving it a bumpy appearance

Golgi apparatus

cellular organelle formed by a series of flattened, membrane-bound sacs that functions in protein modification, tagging, packaging, and transport

lysosome

an organelle that contains enzymes that break down and digest unneeded cellular components, such as damaged organelles; also important for breaking down foreign material

autophagy

“self-eating”; the process of a cell digesting its own structures

autolysis

“self-destruct” mechanism of a cell in which lysosomes are triggered to release enzymes into the cytoplasm, killing the cell

mitochondrion

a membranous, bean-shaped organelle that is the “energy transformer” of the cell

what is the function of mitochondria?

convert energy stored in nutrient molecules into ATP

ribosome

an organelle that serves as the site of protein synthesis

peroxisome

membrane-bound organelle that contains enzymes primarily responsible for detoxifying harmful substances

reactive oxygen species (ROS)

highly reactive products of many normal cellular processes (e.g. peroxides, free radicals)

oxidative stress

damage to cellular components caused by ROS

mutation

a change in the nucleotide sequence in a gene within a cell’s DNA, potentially altering the protein coded by that gene

cytoskeleton

a group of fibrous proteins that provide structural support for the cell; critical for cell motility, cellular reproduction, and transport of substances within the cell

what are the three components of the cytoskeleton?

microtubule, microfilament, intermediate filament

microtubule

a structural filament composed of subunits of tubulin protein; help maintain cell shape and structure, resist compression of the cell, position organelles within the cell

cilia

small appendage on certain cells formed by microtubules and modified for movement of materials across the cellular surface

name a few places in the human body where cilia are found.

lining the airways of the respiratory system, lining the fallopian tubes

flagellum

an appendage specialized for cell locomotion

what is the only flagellated cell in humans?

sperm

centriole

mall, self-replicating organelle that provides the origin for microtubule growth and moves DNA during cell division

microfilament

a thinner type of cytoskeletal filament composed primarily of actin subunits; support muscle contraction and cellular structural support

intermediate filament

type of cytoskeletal filament made of keratin, characterized by an intermediate thickness, and playing a role in resisting cellular tension

some cells, like muscle cells, are “multinucleated”, meaning that they:

contain more than one nucleus

true or false: mammalian red blood cells (RBCs) are multinucleated

false; mammalian RBCs eject their nuclei as they mature, causing their lifespan to be short and requiring the body to constantly produce more of them

nuclear envelope

membrane surrounding the nucleus consisting of two adjacent lipid bilayers with a thin fluid space between them

nuclear pore

a tiny passageway for the passage of proteins, RNA, and solutes between the nucleus and cytoplasm

nucleolus

a region of the nucleus responsible for manufacturing RNA necessary for construction of ribosomes

chromatin

strands of DNA and associated proteins within the nucleus

histone

family of proteins that associate with DNA in the nucleus to form chromatin

nucleosome

unit of chromatin consisting of a DNA strand wrapped around histone proteins

chromosome

condensed version of chromatin

cells must reproduce in order for an organism to:

grow, develop, maintain its health

only very few types of cells in the body don’t divide; these include:

nerve cells, skeletal muscle fibers, cardiac muscle cells

a DNA molecule is made of two __________, ___________ strands arranged in a ______ _____ shape.

complementary, antiparallel, double helix

the four DNA bases are:

adenine (A), thymine (T), cytosine (C), guanine (G)

adenine (A) will always bond with:

thymine (T)

cytosine (C) will always bond with:

guanine (G)

DNA replication

process of duplicating a molecule of DNA; necessary before cell division can take place

the three stages of DNA replication are:

initiation, elongation, termination

what happens during the initiation stage of DNA replication?

the enzyme helicase separates the two strands of a double helix

helicase

enzyme that functions to separate the two DNA strands of a double helix during DNA replication

describe the elongation stage of DNA replication.

each strand becomes a template along which a new complementary strand is built base by base until the template strand is fully complemented

DNA polymerase

enzyme that functions in adding new nucleotides to a growing strand of DNA during DNA replication

describe the termination stage of DNA replication.

DNA replication is stopped once the two original strands are bound to their own finished complementary strands

semiconservative replication

when half of an original DNA molecule is conserved in each new DNA molecule

genome

the entire complement of an organisms DNA, found within virtually every cell