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the study of cell structure and function

sex cells

sperm and oocytes (reproductive cells)

somatic cells

all cells in the body except reproductive cells (sperm and oocytes)


cell substance between the cell membrane and the nucleus, containing the cytosol, organelles, cytoskeleton, and various particles.


fluid portion of cytoplasm

cells come from

division of preexisting cells

smallest units that perform physiological functions


each cell maintains its own state of ___


somatic cells

all body cells except sex cells (sperm and oocytes)

plasma membrane

physical barrier separating cytoplasm from the extracellular environment

functions of plasma membrane

-barrier separating cytoplasm from extracellular fluid
-controls entry of nutrients and ions
-controls elimination of wastes
-receptors monitor environment and instigate needed changes in the cell
-structural support by attachment to other cells or material

phospholipid bilayer

plasma membrane is made of two layers of lipids

hydrophilic layer of plasma membrane

the outer surface of the membrane

hydrophobic layer of plasma membrane

the internal layer of the membrane

contains more K+, cytosol or extracellular fluid?

cytosol contains more potassium

contains more Na+, cytosol or extracellular fluid?

extracellular fluid contains more sodium

two classes of membrane proteins

1- integral proteins
2- peripheral proteins

integral membrane proteins

are a permanent part of membrane structure

peripheral membrane proteins

bound to the inner or outer surface of the membrane and can be removed without causing damage to the membrane

anchoring proteins

stabilize the cell by attaching it to other structures outside of cell and to the cytoskeleton inside the cell

recognition proteins (identifiers)

allow the immune system cells to recognize cells as "self" or "foreign"


catalyze chemical reactions inside or outside of the cells

receptor proteins

sensitive to ligands which trigger changes in cellular activity


extracellular molecules that bind to receptors which then trigger changes is cellular activity

carrier proteins

bind solutes and transport them across cell membranes


proteins with a central pore that forms a passageway across the membrane to permit movement of water and solutes


carbohydrates (glycoproteins, glycolipids, proteoglycans) that extend beyond surface of the plasma membrane forming a viscous layer for lubrication, protection, act as receptors and aid in recognition by immune cells.


fluid portion of cytoplasm


the material between the plasma membrane and the nuclear membrane including cytosol, organelles, solutes, etc

which contains more suspended proteins cytosol or extracellular fluid?

cytosol contains more suspended proteins

cytosol contains reserve stores of ___ ___ and ___

carbohydrates, amino acids and lipids


masses of insoluble materials in cytosol (usually stored nutrients)


internal structures that perform specific tasks to maintain the health and life of the cell (the cells organs)

nonmembranous organelles

organelles not enclosed in a membrane. it's components are in direct contact with cytosol (cytoskeleton, centrioles, cilia, ribosomes, proteosomes)

membranous organelles

organelles isolated from cytosol with phospholipid membranes (edoplasmic reticulum, Golgi apparatus, lysosomes, peroxismes, mitochondria and nucleus)


internal protein framework that provides cytoplasm with strength and structure. Made up of microfilaments, intermediate filaments and microtubules.


smallest element of cytoskeleton. composed of the protein actin.

functions of microfilaments

-anchor cytoskeleton to integral proteins on plasma membrane
-produce movement or change shape of cell

intermediate filaments

filaments of cytoskeleton that are larger than microfilaments but smaller than thick filaments. Made of various proteins. They are the most durable part of the cytoskeleton.

functions of intermediate filaments

-stabilize organelles
-maintain cell shape (along with microfilaments)
-attach to plasma membrane to stabilize cell position


largest component of cytoskeleton. made up of protein called tubulin. they start at the centrosome and extend out into cytoplasm.

functions of microtubules

-provide cell strength and anchor organelles
-can be disassembled and reassembled to change shape of cell
-used as a system to move vesicles and other organelles inside of cell
-form spindle apparatus during cell division to move chromatids around inside of the nucleus

thick filaments

massive filament bundles composed of the protein myosin. They appear only in muscle cells and produce muscle contraction.


small finger-like projections on the surface of cells that absorb large amounts of material from extracellular fluid (such as cells lining the digestive tract). They increase the surface area of the cell so it is exposed to more of the extracellular environment.


cylindrical structures composed of microtubules that are found in all cells capable of cell division. They are made of 9 microtubules grouped in triplets (9+0 array). During cell division they form the spindle apparatus for moving chromatids around inside of nucleus. Microtubules begin here and project outward.


the region of cytoplasm that surrounds the centrioles


long, slender, hair-like extensions of the plasma membrane of some cells in respiratory and reproductive systems. They are made of 9 pairs of microtubules surrounding a central pair (9+2 array). The microtubules are anchored a basil body. They beat rhythmically to move fluid or secretions across the cell surface.

function of ribosomes

responsible for protein synthesis

the two subunits of ribosomes

small ribosomal unit and large ribosomal units. The two must join together with mRNA for protein synthesis to occur

two types of ribosomes

1- free ribososmes
2- fixed ribosomes

free ribosomes

scattered throughout cytoplasm. synthesize proteins that enter the cytosol for use inside the cell

fixed ribosomes

attached to rough ER (endoplasmic reticulum). They make proteins that are modified and packaged by ER for secretion outside of the cell

function of proteosomes

they remove proteins from cytoplasm that are damaged or abnormal (like those released from virus infected cells) and break them down to recycle the unable parts of the damaged protein


enzymes found in proteosomes that digest abnormal proteins making them proteolytic


third stage

endoplasmic reticulum

network of flat sacs, hollow tubes and chambers (cisternae) connected to the nuclear membrane that:
-aid in protein synthesis
-store materials
-transport materials
-absorb and neutralize drugs and toxins

two types of endoplasmic reticulum

smooth ER- has smooth surface
rough ER- has ribosomes along its outer surface

smooth ER function

-synthesizes lipids and carbohydrates for structure of other organelles
-synthesizes steroids and hormones
-synthesizes and stores glycogen in liver and muscle cells
-adjusts contents of cytosol by absorbing and storing excess substances (ie- Ca++, etc)
-detox of drugs/toxins in liver and kidney cells

rough ER function

proteins newly made by ribosomes on its surface are packaged and modified for export to next destination (most are packaged in transport vesicles for delivery to golgi apparatus

transport vesicle

membranes formed around proteins modified by the rough ER that then transport the proteins to their next destination (usually the golgi apparatus)

golgi apparatus

looks like a stack of flattened sacs (cisternae). located near the nucleus. prepares proteins that it receives from the rough ER for exocytosis (enzymes, hormones, etc). It also packages special enzymes in vesicles for use in cytoplasm.


flattened sacs that contain fluid in the ER and golgi apparatus


digestive vesicles produced by the golgi apparatus that provide an isolated environment for dangerous chemical reactions within the cell (ie- the breakdown of large organic molecules).

primary lysosomes

contain inactive enzymes. once they fuse with the material to be digested their enzymes become activated and they become secondary lysosomes.

secondary lysosomes

lysosomes that have fused with material to be digested and now contain active digestive enzymes

functions of lysosomes

-digest and recycle damaged organelles
-destroy bacteria, organic compounds or liquids that enter the cell
-after digestion of materials, the nutrients are released into cytosol and the unusable waste is eliminated through exocytosis


a cell is damaged and it's lysosomes disintegrate eleasing digestive enzymes into the cytoplasm. The enzymes rapidly destroy the cell's organelles, proteins and plasma membrane.

proteins made in the ___ ribosomes are released into cytoplasm for use in the cell.

free ribosomes make proteins for use in the cell

proteins made in the ___ ribosomes are folded and packaged to moved to the ER.

fixed ribosomes make proteins that then move into the ER and are eventually used outside of the cell

secretory vesicles

vesicles made in the golgi apparatus that fuse with the plasma membrane and release their contents outside of the cell (exocytosis)

membrane renewal vesicles

vesicles made in the golgi apparatus that add new proteins and lipids to the plasma membrane

steps of protein synthesis

1- mRNA leaves nucleus and attaches to ribosomes
2- ribosomes form the protein coded by the mRNA from amino acids
3- proteins made by free ribosomes move into cytoplasm, if made by fixed ribosomes proteins move into the ER
4- proteins are modified in hollow tubes of ER
5- a region of ER buds off forming a transport vesicle around the protein
6- transport vesicle moved protein to the golgi apparatus
7- enzymes modify protein in cisternae of GA and then they moved through and are released in vesicles on the other side of the golgi apparatus


vesicles that are smaller than lysosomes and contain digestive enzymes for breakdown of fatty acids. They protect the cell from hydrogen peroxide (H2O2) which is a free radical byproduct of fatty acid digestion.


the main enzyme responsible for breaking down hydrogen peroxide in peroxisomes. It is produced by free ribosomes and carried to peroxosomes by carrier proteins.

membrane flow

the repair, recycling and changes in composition that the plasma membrane goes through to adapt to environmental changes


"powerhouse of the cell" responsible for energy (ATP) production via the breakdown of carbohydrates

cristae of mitochondria

the many folds of the inner membrane of the mitochondria that contains the fluid contents (matrix)

mitochondrial matrix

the fluid inside the cristae of the mitochondria

most chemical reactions that release energy occur in the ___


most chemical reactions that use energy occur in the ___


steps of mitochondrial energy production (aerobic respiration b/c O2 is the final electron acceptor)

1- glycolysis occurs in the cytoplasm (1 glucose is broken down into 2 pyruvate molecules)
2- mitochondria absorbs pyruvate
3- in matrix CO2 is removed from pyruvate
4- Citric acid cycle (Krebs cycle) occurs
5- CO2 is released as waste
6- hydrogen produced by krebs cycle is oxidized electron transport chain
7- ATP is produced

mitochondria absorb ___ and ___ and generate ___ and ___.

absorb pyruvate and O2 and generate CO2 and ATP


largest organelle. control center of cell. determines structure and function of the cell.

nuclear envelope

double membrane that separates nucleus from cytosol

perinuclear space

the space between the two layers of the nuclear envelope

what organelle is externally connected to the nuclear envelope?

the rough ER

nuclear pores

large proteins in nuclear envelope that allow chemical communication between nucleus and cytoplasm


the fluid in the nucleus

nuclear matrix

network of filaments in nucleoplasm that provide structure and support


transient organelles inside nucleus that synthesize rRNA and produce the ribosomal subunits


complex formed by double helix DNA strands wound around a core of histones


when cells are not dividing, nucleosomes are loosely coiled (a tangled mess)


the form that nucleosomes take on when they coil tightly just before cell division

humans have how many pairs of chromosomes?


genetic code

the chemical language the cell uses to code for functional products

the nitrogenous bases of complementary DNA strands are held together by ___ bonds

hydrogen bonds

triplet code

the identity of a single amino acid is stored in sequences of three nitrogenous bases


the functional unit of heredity. contains all the DNA triplets needed to produce specific proteins

gene activation

before protein synthesis the hydrogen bonds between nucleotides are broken, the histones are removed and RNA polymerase binds to the promoter site on the DNA


"to copy" -its the synthesis of RNA using DNA as a so that the info can be taken to the ribosomes by mRNA for protein synthesis

mRNA (messenger RNA)

is made in the nucleus during transcription using DNA as a template. mRNA then takes the info for protein synthesis into the cytoplasm to bind ribosomes

RNA polymerase

enzyme that creates RNA from DNA

coding strand

one of the two strands of DNA. during transcription this is the strand that contains the genes for specific proteins

template strand

one of the two strands of DNA. during transcription, this strand is complementary to the coding (functional) strand so when a strand of RNA complementary to the template strand is made, it is identical to the coding strand of DNA


three nucleotide bases on RNA that are complementary to a triplet of bases on the template DNA strand (which makes them identical to a triplet on the coding (functional strand)

RNA processing

after transcription, all of the nonsense regions of RNA that are not needed to build a protein are removed and all of the necessary regions are spliced together

protein synthesis

the assembling of a functional polypeptide


formation of a linear chain of amino acids using the info provided by a strand of mRNA (translated from mRNA language to amino acid language)

tRNA (transfer RNA)

acts as a transfer truck, it delivers the appropriate amino acids to the ribosome that are needed to build the peptide coded by the mRNA attached to the ribosome


sequence of three bases on mRNA


sequence of three bases on tRNA that are complementary to codons on mRNA.

protein synthesis summary

1-gene activation- DNA is uncoiled and histones removed
2-transcription- mRNA is made from DNA in nucleus
3-mRNA moves to cytoplasm
4-mRNA binds ribosomes
5-translation- tRNA binds ribosomes and tRNA delivers amino acids coded by mRNA to form the specific protein


passive movement of a solute from an area of high concentration to an area of low concentration (down the concentration gradient)

concentration gradient

the difference between high and low concentrations of a substance

factors that affect diffusion

-concentration gradient
-molecule size
-electrical current

the two ways an ion or molecule can diffuse across the plasma membrane

1-crossing the lipid portion of the membrane
2-passing through a membrane channel

membrane channels

passageways through proteins in the plasma membrane

leak channels

passive channels that are permanently open to allow passage across membrane


movement (diffusion) of water across membrane. "water follows salt" -water moves towards area with higher solute concentration

osmotic pressure

the force with which water moves into a solution because of its solute concentration

hydrostatic pressure

pressure against fluid

most membranes are freely permeable to ___



total solute concentration of a solution


how the fluid affects the cell (fluid shift)


causes no fluid shift


less solute than the cell. causes water to flow into the cell


more solute than the cell, causes water to flow out of the cell


water flows into a red blood cell in a hypotonic solution causing it to swell and rupture


fluid leaves the cell when placed in a hypertonic solution which causes the cells to dehydrate and shrivel up

carrier mediated transport

proteins bind specific molecules and carry them across the plasma membrane


when a carrier protein can bind more than one type of molecule and transport two substances the same direction at the same time


carrier protein transports one substance into cell and then binds a different substance and transports it out of the cell

two types of carrier mediated transport

facilitated diffusion
active transport

facilitated diffusion

carrier proteins transport substances across membrane down the concentration gradient (uses no ATP)

active transport

carrier proteins move molecules against the concentration gradient. requires ATP

ion pumps

carrier proteins that move sodium, potassium, calcium and magnesium across membranes

exchange pumps

ion pumps that perform countertransport

sodium-potassium ATPase

the carrier protein sodium-potassium carrier protein that is active is sodium-potassium exchange pumps

secondary active transport

doesn't use ATP for transport but must use it to maintain homeostasis after the transport (ex- glucose can be transported into the cell with sodium but later ATP is required to move sodium back out of the cell)

vesicular transport

materials are moved in or out of the cell in vesicles that form at, or fuse with, the plasma membrane

two types of vesicle transport



extracellular materials (fluids and solutes) are packaged in vesicles at the cell membrane and brought into the cell. Lysosomes then bind to the vesicle and digest it or digest the material inside for use by the cell.

three types of endocytosis

1-receptor mediated

receptor mediated endocytosis

when a specific target ligand binds the receptors on plasma membrane the ligand is then enclosed in a vesicle and brought into the cell


"cell drinking" -extracellular fluid is brought into the cell in vesicles


uses pseudopods to engulf a large solid object (bacteria, etc) and form a vesicle around the object bringing it into the cell for digestion/destruction


vesicle inside of the cell moves towards the plasma membrane and fuses with it, vesicle contents are released outside the cell. used to expel hormones, waste products, etc.

types of passive transport (dont require ATP)

simple diffusion, osmosis, facilitated diffusion

types of transport that require ATP

active transport, secondary active transport, endocytosis and exocytosis

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