Biology 2 - Cells

Front 1

Golgi apparatus

Back 1

– The Golgi apparatus
processes, sorts, and ships
proteins synthesized in the
rough ER.
– Membranous vesicles
carry materials to and
from the organell

Front 2

The smooth endoplasmic
reticulum (smooth ER,
SER)

Back 2

Enzymes within the smooth
ER may synthesize fatty
acids and phospholipids, or
break down poisonous
lipids.
– Reservoir for Ca
2+
ion

Front 3

rough endoplasmic reticulum
(rough ER, RER

Back 3

Ribosomes associated with the
rough ER synthesize proteins.
– New proteins are folded and
processed in the rough ER lumen

Front 4

Peroxisome

Back 4

Center of oxidation
reaction

Front 5

glyoxysomes

Back 5

Specialized peroxisomes in plants called glyoxysomes
are packed with enzymes that oxidize fats to form a
compound that can be used to store energy for the cell.

Front 6

Lysosomes

Back 6

singlemembrane-bound
structures containing
approximately 40
different digestive
enzymes

Lysosomes are used for
digestion and waste
processing

Front 7

Materials are delivered to the lysosomes by three processes

Back 7

Phagocytosis
– Autophagy
– Receptor-mediated endocytosi

Front 8

Phagocytosis

Back 8

Cell eating

Front 9

Endocytosis

Back 9

is a process by which the cell membrane can pinch off
a vesicle to bring outside material into the cell

Front 10

Autophagy

Back 10

Organelles that are old and worn out are digested by lysosome

Front 11

Vacuole

Back 11

are large membranebound structures found in plants
and fungi.
– Some contain digestive
enzymes


– Some vacuoles are specialized
for digestion.
– Most vacuoles are used for
storage of water and/or ions to
help the cell maintain its normal volume

Front 12

Endosymbionts

Back 12

Mitochondrion - Aerobic ATP production

Chloroplast - Photosynthesis

Front 13

Cell wall

Back 13

Fungi, algae and plants have stiff outer cell walls that protect the cell

In plants and algae and plants primarily made of cellulose, in fungi primary component chitlin

Front 14

Lignin

Back 14

Some plants have a secondary cell wall containing lignin

Front 15

Cytoskeleton

Back 15

composed of
protein fibers, gives the cell
shape and structural stability,
and aids cell movement and
transport of materials within the cell.

In essence, the cytoskeleton
organizes all of the organelles
and other cellular structures into a cohesive whole

Front 16

How many ATP molecules per second can be synthesized by the body's cells?

Back 16

10 million

Front 17

Cellular enzymes can catalyze......reactions per second

Back 17

>25000

Front 18

endomembrane system

Back 18

is composed of the smooth and rough ER and the Golgi apparatus, and is the primary system for protein and lipid synthesis and membrane synthesis and turnover

Front 19

Single Hypothesis

Back 19

predicts that proteins and other macromolecules have a "zip code" or signal sequence that directs them to a particular location in the cell

Front 20

Motor proteins

Back 20

microtubles have "rails" that allow proteins to move along the microtuble in one direction

Front 21

Nuclear Localization signal (NLS)

Back 21

17-amino-acid-long protein that allow them them enter the nucleus

Front 22

How do the microvilli in the intestine keep their shape?

Back 22

their structure surrounds a microfilliment skeleton (30-40 microfillaments)

Front 23

secretory pathway hypothesi

Back 23

the pathway for secretion is conserved in cells, a specific pathway. Their synthesis and travel is all organized

Front 24

The signal hypothesis

Back 24

1.)Signal sequence is synthesized
2.)Signal binds to SRP
3.)SRP binds to receptor
4.)Protein in synthesized into ER
5.)Protein synthesis is complete

Front 25

How are proteins transported from the ER to the golgi apparatus?

Back 25

in
vesicles that bud off the ER, then fuse with the Golgi apparatus
membrane and deposit their contents inside

Front 26

When a protein comes out of the golgi?

Back 26

Each protein that comes out
of the Golgi apparatus has a
molecular tag that places it in
a particular type of transport
vesicle.
Each type of transport
vesicle also has a tag that
allows it to be transported
to the correct destination

Front 27

Exocytosis

Back 27

Some proteins are sent to the cell surface in vesicles that fuse with
the plasma membrane, releasing their contents to the exterior of the
cell

Front 28

Cytoskeleton

Back 28

complex network of fibers that helps
maintain cell shape by providing structural support. The
cytoskeleton is dynamic; it changes to alter the cell’s shape, to
transport materials in the cell, or to move the cell itself

Front 29

Three types of cytoskeletal elements?

Back 29

Actin filaments (microfilaments)
Intermediate filaments
Microtubules

Front 30

Actin filaments

Back 30

Smallest cytoskeletal elements

actin filaments form by polymerization of individual actin molecules

actin filaments are grouped together into long bundles or dense networks that are usually found just inside the plasma membrane and help define the celll’s shape

Actin filaments can also be involved in movement by interacting
with the motor protein myosin

Actin-myosin interactions can cause cell movements such as cell crawling, cytokinesis, and cytoplasmic streaming

Front 31

Intermediate filaments

Back 31

defined by size rather than
composition. Many types of intermediate filaments exist, each consisting of a different protein.

Intermediate filaments provide structural support for the cell. They are not involved in movement

Intermediate filaments form a flexible skeleton that helps shape the cell surface and hold the nucleus in place

Front 32

Microtubules

Back 32

e large, hollow tubes made of tubulin dimers

Microtubules have polarity, are dynamic, and usually grow at their plus ends

Microtubules originate from the microtubule organizing center
and grow outward, radiating throughout the cell

Animal cells have just one microtubule organizing center called the
centrosome. Centrosomes contain two bundles of microtubules called centrioles

Front 33

Microtubule function?

Back 33

Microtubules provide stability and are involved in movement, they may also provide a structural framework for organelles

can act like railroad tracks, transport vesicles move through the cell along these microtubule tracks in an energy-dependent process

Front 34

What do microtubules require for vesicle transportation to occur?

Back 34

ATP, kinesin and dyneins

Front 35

Kinesin and dyneins?

Back 35

motor proteins that convert chemincal energy in ATP into mechanical work

Front 36

How does Kinesin work?

Back 36

it walks along the microtubule track (like walk cannot completely let go until other portion has connected)

Front 37

Flagella

Back 37

long hairlike projections from the cell surface that move cells

Front 38

Difference between bacterial flagella and eukaryotic flagella?

Back 38

bacterial flagella are made of flagellin and rotate like a propeller

Eukaryotic flagella are made of microtubules and wave back and forth

Front 39

plasmodesmata

Back 39

Connection between plant cells, gaps in the cell wall
where the plasma membranes, cytoplasm, and smooth ER of two
cells connec

Front 40

gap junctions

Back 40

connect adjacent cells by
In animal cells,forming channels that allow the flow of small molecules between
cells

Front 41

How do distant cells communicate?

Back 41

The activities of cells, tissues, and organs in different parts of a multicellular organism are coordinated by long distance signals

Front 42

Hormone

Back 42

s an information-carrying molecule that is secreted
from a cell, circulates in the body, and acts on target cells far from the signaling cell.

Front 43

Are hormones small or large molecules?

Back 43

They are small molecules and are in minute concentrations but they have a large impact on the condition of the organism as a whole

Front 44

Lipid-soluable hormones

Back 44

usually diffuse across the plasma membrane into their target cells' cytoplasm

Front 45

Lipis-insoluble hormones

Back 45

large or hydrophilic and do not cross the plasma membrane but instead bind to a receptor on the cell's plasma membrane

Front 46

Auxin

Back 46

-Small organic compound
-Signal received at plasma membrane
-signals changes in long axis of plant body

Front 47

Brassinosteriods

Back 47

-Steroid
-At plasma membrane
-stimulate plant cell elongation

Front 48

Estrogens

Back 48

-Steroid
-Inside cell
-Stimulate development of female characteristics

Front 49

Ethylene

Back 49

-C2H4 (gas)
-At plasma membrane
-Stimulates fruit ripening, regulates aging

Front 50

FSH

Back 50

-Glycoprotein
-At plasma membrane
-Stimulates egg maturation, sperm production

Front 51

Insulin

Back 51

-Protein, 51 amino acids
-At plasma membrane
-stimulates glucose uptake in animal bloodstream

Front 52

Prostaglandins

Back 52

-Modified fatty acid
-at plasma membrane
-perform a variety of functions in animal cells

Front 53

Systemin

Back 53

-Peptide, 18 amino acid
-at plasma membrane
-Stimulates plant defenses against herbivores

Front 54

Thyroxine(T4)

Back 54

-Modified Amino Acid
-Inside cell
-Regulates metabolism in animals

Front 55

Four steps of Cell-cell signaling?

Back 55

1.) Signal reception
2.) Signal processing
3.) Signal response
4.) Signal deactivation

Front 56

Signal reception

Back 56

-Hormones bind to signal receptors (the presence of an appropriate receptor protein dictates which cells will be able to respond to a particular hormone)
-Identical receptors in diverse cells and tissues allow long-distance signals to coordinate the activities of cells throughout a multicellular organism

Front 57

Signal receptors

Back 57

-Protein that change their shape or activity after binding to a signaling molecule
-receptors are dynamic and may change their sensitivity to particular hormones
-Receptors can be blocked
-receptors that bind to lipid-soluble hormones are located inside the cells, but most signal receptors are located in the plasma membrane

Front 58

Signal processing

Back 58

-Lipid-soluble hormones that cross the plasma membrane produce different cell responses from lipid-insoluble hormones that bind to membrane receptors
-Lipid-soluble steroid hormones bind to receptors inside the cell and triggar a change in the cell's activity directly
-In this case the hormone-receptor complex transported to the nucleus, where it alters gene expression

Front 59

Signal processing in lipid-insoluble hormones

Back 59

-bind to membrane receptors
-when it binds to the cell surface it triggers a complex series of events, collectively called a signal transduction pathway which converts the extracellular hormone signal to an intracellular signal
-The message trasnmitted by a hormone is amplified as it changes form

Front 60

Signal tranduction and amplification

Back 60

occurs in the plasma membrane and inside the cell

Front 61

G-protein or enzyme linked receptors

Back 61

G-proteins trigger the production of an intracellular messenger
-enzyme-linked receptors trigger the activation of a series of proteins inside the cell

Front 62

G-protein

Back 62

intracellular peripheral membrane proteins that are closely associated with transmembrane signal receptors
-are activated when they bind GTP and are deactivated when they hydrolyze the bound GTP to GDP

Front 63

What are the steps of linking an external signal to the production of an intracellular signal?

Back 63

1.) Hormone binds to the membrane receptor, which changes shape and activates G proteins
2.)G protein exchanges GDP for GTP and splits into two parts
3.) One part of the G protein activates a membrane enzyme, which catalyzes the production of a second messenger

Front 64

Second messengers

Back 64

small molecules that diffuse rapidly throughout the cell, amplifying the hormone signal
-several second messengers work my activating protein kinases, which add a phosphate group to, or phosphorylate, orther proteins

Front 65

enzyme-linked receptors

Back 65

are transmembrane proteins that bind a hormone signal and directly catalyze a reaction inside the cell
-Best known group are receptor tyrosine kinases (RTKs)

Front 66

Five steps of directly catalyzing an intracellular reaction involves 5 steps:

Back 66

1.) Hormone binds to an RTK
2.) RTK froms a dimer and is phosphorylated by ATP
3.) proteins build a bridge between RTK and the Ras protein, which is subsequently activated
4.) Ras triggers the phosphorylation and activation of another protein
5.) Phosphorylation cascade, with each phosorylated protein catalyzing the phosphorylation of other proteins, amplifies the original signal many times over

Front 67

Four components of cellular respiration

Back 67

Glycolysis, pyruvate processing, citric acid cycle, electron transport and chemisomosis

Front 68

Cellular repiration

Back 68

the oxidative metabolism that converts energy stored in chemical bonds into energy used by cells

Front 69

ATP

Back 69

adenosine triphosphate - energy source

Cellular currency for energy, high potential energy and allows cells to do work

works by phosphorylating (transfer of a phosphate group) target molecules

Front 70

Why do ATP molecules have high potential energy?

Back 70

four negative charges in its 3 phosphate groups, which repel each other

Hydrolysis of the bond between the two outermost phosphate groups results in formation of ADP and P and the released phosphate group is transferred to a protein

Front 71

Why is the hydrolysis of ATP exergonic?

Back 71

because the entropy of the product molecules is much higher than that of the reactants

Front 72

What happens to the protein when ATP hydrolysis causes a phosphate group to be transferred to that protein?

Back 72

causes a change in the proteins shape or conformation

Front 73

How does ATP drive endergonic reactions?

Back 73

When protein is phosphorlylated, the exergonic phosphorlylation reaction is paired with an endergonic reaction in a process that is called energetic reaction coupling

in cells endergonic reactions become exergonic when the substrates or enzymes involved are phosphorylated

in energy coupled reactions there is a common intermediate where the product of the first reaction becomes the substrate in the second

Front 74

How does reaction coupling use free energy?

Back 74

The free energy of sequential reaction is additive

reaction coupling uses the free energy of one reaction to change the extent of another "driving" it further towards completion


in energy coupled reactions there is a common intermediate where the product of the first reaction becomes the substrate in the second

Front 75

What are the functions of ATP

Back 75

Mechanical work - Suchas the movement of proteins in muscles

transport work - such as the movement of substances across membranes

Chemical work - such as making complex molecules out of simple molecules

Electrical work - such as nerve activity in the brain

Front 76

What is potential energy based on?

Back 76

generally electrons and their position relative to positive and negative charges

Front 77

What happens when glucose is oxidized?

Back 77

the carbon atoms of glucose are oxidized to for carbon dioxide, and the oxygen atoms are reduced to form water

Front 78

Cellular respiration

Back 78

also called aerobic respiration requires oxygen

Front 79

Locations for energy pathways

Back 79

External to the mitochonrion - Glycolysis, fememntation

Inside mitochondrion - inner membrane: pyruvate oxidation, respiratory chain
Matirix: citric acid cycle

Front 80

Glycolysis

Back 80

1) 6 carbon glucose molecule is brokem down into two 3-carbon pyruvic acid molecules
-occurs in the fluid cytosol
-does not require oxygen
-Makes very little ATP

Front 81

Pyruvate Processing

Back 81

Molcules move across the two mitochondrial membranes and into the matrix of the mitochondria where the citric acid cycle begins

Front 82

Tricarboxylic acid cycle/krebs cycle/ citric acid cycle

Back 82

the pyruvic acid molecules undergo many enzymatic steps in the mitochondrial matrix
-they are completely broken down
-the krebs cycle strips them of carbon dioxide and electrons and carbon dioxide is released

Front 83

The electron Transport Chain

Back 83

In a series of proteins in the inner mitochondrial membrane
-passes electrons down the chain to be picked up eventually by oxygen
-pulls H+ ions across the membrane into the inner membrane space
-the collection of H+ in the inner membrane creates an electrochemical gradient
-the H+ ions cannot pass directly through the membrane
-they travel through a transport protein in the inner membrane
-this transport protein has an additional job, it acts as an ATP Synthase enzyme, uses kinetic energy to H+ to phosphoylate ADP into ATP

Front 84

Where are all the enzymes needed for glycolysis?

Back 84

Cytosol

Front 85

In glycolysis what happens to glucose?

Back 85

Its broken into two 3-carbon molecules of pyruvate and potential energy is released that is used to phosphorylate ADP to form ATP

Front 86

What are the phases of Gylcolysis?

Back 86

Energy investment phase: two molecules of ATP are consumed and glucose is phosphorylated twice, forming fructose 1, 6-biphosphate

Energy payoff: Sugar is split to form two pyruvate molecules, two molecules NAD+ are reduced to NADH, four molescules of ATP are formed by substrate-level phosphorylation (net gain of 2 ATP)

Front 87

Substate-level phosphorylation

Back 87

occurs when ATP is produced by the enzyme-catalyzed transfer of phosphate group an intermediate substrate to ADP

Front 88

Feedback inhibition

Back 88

Occurs when an enzyme in a pathway is inhibited by the product of that pathway

-cells that are able to stop glycolytic reactions when ATP is abundant can conserve their stores of glucose for times when ATP is scarce

Front 89

Phosphofructokinase

Back 89

Is released during glycolysis by high levels of ATP and catalyzes the early reactions

Has two binding sites for ATP
1) the active site, where ATP phosphorylates fructose-6-phosphate, resulting in the synthesis of fructose-1,6-biphosphate
2)a regulatory site

high concentrations of ATP cause ATP to bind to the regulatory sit, changing the enzyme's shape and dramatically decreasing the reaction rate at the active site

Front 90

Pyruvate processing and its regulation

Back 90

second step in glucose oxidation, catalyzed by the enzyme pyruvate dehydrogenase in the matrix

pyruvate processing is under both positive and negative control. Abundant ATP reserves inhibit the enzyme complex

in the presence of O2, pyruvate undergoes a series of reactions that results in the product molecule acetly coenzyme ! (acetyl CoA)

Front 91

Substrates of the citric acid cycle

Back 91

carboxylic acid, citrate and oxaloacetate

Front 92

The electron transport chain

Back 92

high potential energy of electrons carried by NADH and FADH2 is gradually decreased as they move through a series of redox reactions

the proteins involved in these reactions make up what is called an ETC

O2 is the final electrol acceptor, the transfer of electrons alongn with protons to oxygen forms water

Front 93

Proton-motive force

Back 93

when ETC pumps protons from the mitochondrial matrix into the intermembrane space this force from the electrochemical gradient can be used to make ATP in a process known as chemiosmosis

Front 94

How is the ETC organized?

Back 94

proteins are organized into four large multiprotein complexes and cofactors

Front 95

Cytochrome c

Back 95

transfer electrons between complexes

Front 96

actin

Back 96

A globular protein that can be polymerized to form filaments. Actin filaments are part of the cytoskeleton and constitute the thin filaments in skeletal muscle cells.

Front 97

actin filament

Back 97

A long fiber, about 7 nm in diameter, composed of two intertwined strands of polymerized actin protein; one of the three types of cytoskeletal fibers. Involved in cell movement. Also called a microfilament. Compare with intermediate filament and microtubule.

Front 98

autophagy

Back 98

The process by which damaged organelles are surrounded by a membrane and delivered to a lysosome to be destroyed.

Front 99

axoneme

Back 99

A structure found in eukaryotic cilia and flagella and responsible for their motion; composed of two central microtubules surrounded by nine doublet microtubules (9 + 2 arrangement).

Front 100

basal body

Back 100

A structure of nine pairs of microtubules arranged in a circle at the base of eukaryotic cilia and flagella where they attach to the cell. Structurally similar to a centriole.

Front 101

cell crawling

Back 101

A form of cellular movement involving actin filaments in which the cell produces bulges (pseudopodia) that stick to the substrate and pull the cell forward. Also called amoeboid motion.

Front 102

centriole

Back 102

One of two small cylindrical structures, structurally similar to a basal body, found together within the centrosome near the nucleus of a eukaryotic cell.

Front 103

centromere

Back 103

Constricted region of a replicated chromosome where the two sister chromatids are joined and the kinetochore is located.

Front 104

cilium

Back 104

One of many short, filamentous projections of some eukaryotic cells containing a core of microtubules. Used to move the cell and/or to move fluid or particles along a stationary cell. See axoneme.

Front 105

cytoplasmic streaming

Back 105

The directed flow of cytosol and organelles that facilitates distribution of materials within some large plant and fungal cells. Occurs along actin filaments and is powered by myosin.

Front 106

dynein

Back 106

A class of motor proteins that use the chemical energy of ATP to “walk” along an adjacent microtubule. Dyneins are responsible for bending of cilia and flagella, play a role in chromosome movement during mitosis, and can transport certain organelles.

Front 107

endoplasmic reticulum (ER)

Back 107

A network of interconnected membranous sacs and tubules found inside eukaryotic cells. See rough endoplasmic reticulum and smooth endoplasmic reticulum.

Front 108

Golgi apparatus

Back 108

A eukaryotic organelle, consisting of stacks of flattened membranous sacs (cisternae), that functions in processing and sorting proteins and lipids destined to be secreted or directed to other organelles. Also called Golgi complex.

Front 109

ER signal sequence

Back 109

A short amino acid sequence that marks a polypeptide for transport to the endoplasmic reticulum where synthesis of the polypeptide chain is completed and the signal sequence removed. See signal recognition particle.

Front 110

kinesin

Back 110

Any one of a class of motor proteins that use the chemical energy of ATP to transport vesicles, particles, or chromosomes along microtubules.

Front 111

granum

Back 111

In chloroplasts, a stack of flattened, membrane-bound vesicles (thylakoids) where the light reactions of photosynthesis occur.

Front 112

glycosylation

Back 112

Addition of a carbohydrate group to a molecule.

Front 113

intermediate filament

Back 113

A long fiber, about 10 nm in diameter, composed of one of various proteins (e.g., keratins, lamins); one of the three types of cytoskeletal fibers. Form networks that help maintain cell shape and hold the nucleus in place. Compare with actin filament and microtubule.

Front 114

lysosome

Back 114

A small organelle in an animal cell containing acids and enzymes that catalyze hydrolysis reactions and can digest large molecules. Compare with vacuole.

Front 115

microtubule

Back 115

A long, tubular fiber, about 25 nm in diameter, formed by polymerization of tubulin protein dimers; one of the three types of cytoskeletal fibers. Involved in cell movement and transport of materials within the cell. Compare with actin filament and intermediate filament.

Front 116

microtubule-organizing center (MTOC)

Back 116

General term for any structure (e.g., centrosome and basal body) that organizes microtubules in cells.

Front 117

myosin

Back 117

Any one of a class of motor proteins that use the chemical energy of ATP to move along actin filaments in muscle contraction, cytokinesis, and vesicle transport.

Front 118

receptor-mediated endocytosis

Back 118

Uptake by a cell of certain extracellular macromolecules, bound to specific receptors in the plasma membrane, by pinching off the membrane to form small membrane-bound vesicles.

Front 119

pulse-chase experiment

Back 119

A type of experiment in which a population of cells or molecules at a particular moment in time is marked by means of a labeled molecule and then their fate is followed over time.

Front 120

ribosome

Back 120

A large complex structure that synthesizes proteins by using the genetic information encoded in messenger RNA strands. Consists of two subunits, each composed of ribosomal RNA and proteins.

Front 121

rough ER

Back 121

The portion of the endoplasmic reticulum that is dotted with ribosomes. Involved in synthesis of plasma membrane proteins, secreted proteins, and proteins localized to the ER, Golgi apparatus, and lysosomes. Compare with smooth endoplasmic reticulum.

Front 122

thylakoid

Back 122

A flattened, membrane-bound vesicle inside a plant chloroplast that functions in converting light energy to chemical energy. A stack of thylakoids is a granum.

Front 123

smooth endoplasmic reticulum (smooth ER)

Back 123

The portion of the endoplasmic reticulum that does not have ribosomes attached to it. Involved in synthesis and secretion of lipids. Compare with rough endoplasmic reticulum.

Front 124

antibody

Back 124

An immunoglobulin protein, produced by B cells, that can bind to a specific part of an antigen, tagging it for attack by the immune system. All antibody molecules have a similar Y-shaped structure and, in their monomer form, consist of two identical light chains and two identical heavy chains.

Front 125

cadherins

Back 125

Any of a class of cell-surface proteins involved in cell adhesion and important for coordinating movements of cells during embryological development.

Front 126

collagen

Back 126

A fibrous, pliable, cable-like glycoprotein that is a major component of the extracellular matrix of animal cells. Various subtypes differ in their tissue distribution.

Front 127

desmosome

Back 127

A type of cell-cell attachment structure, consisting of cadherin proteins, that bind the cytoskeletons of adjacent animal cells together. Found where cells are strongly attached to each other. Compare with gap junction and tight junction.

Front 128

fibronectin

Back 128

An abundant protein in the extracellular matrix that binds to other ECM components and to integrins in plasma membranes; helps anchor cells in place. Numerous subtypes are found in different tissues.

Front 129

gap junction

Back 129

A type of cell-cell attachment structure that directly connects the cytoplasms of adjacent animal cells, allowing passage of water, ions, and small molecules between the cells. Compare with desmosome and tight junction.

Front 130

guanine triphosphate (GTP)

Back 130

A molecule consisting of guanine, a sugar, and three phosphate groups. Can be hydrolyzed to release free energy. Commonly used in many cellular reactions; also functions in signal transduction in association with G proteins.

Front 131

integrin

Back 131

Any of a class of cell-surface proteins that bind to fibronectins and other proteins in the extracellular matrix, thus holding cells in place

Front 132

pectin

Back 132

A gelatinous polysaccharide found in the primary cell wall and middle lamella of plant cells. Attracts and holds water, forming a gel that helps keep the cell wall moist.

Front 133

phosphorylation cascade

Back 133

A series of enzyme-catalyzed phosphorylation reactions commonly used in signal transduction pathways to amplify and convey a signal inward from the plasma membrane.

Front 134

plasmodesmata

Back 134

Physical connection between two plant cells, consisting of gaps in the cell walls through which the two cells' plasma membranes, cytoplasm, and smooth ER can connect directly. Functionally similar to gap junctions in animal cells.

Front 135

quorum sensing

Back 135

Cell-cell signaling in bacteria, in which cells of the same species communicate via chemical signals. It is often observed that cell activity changes dramatically when the population reaches a threshold size, or quorum.

Front 136

Ras protein

Back 136

A type of G protein that is activated by binding of signaling molecules to receptor tyrosine kinases and then initiates a phosphorylation cascade, culminating in a cell response.

Front 137

receptor tyrosine kinase

Back 137

Any of a class of cell-surface signal receptors that undergo phosphorylation after binding a signaling molecule. The activated, phosphorylated receptor then triggers a signal transduction pathway inside the cell.

Front 138

signal receptor

Back 138

Any cellular protein that binds to a particular signaling molecule (e.g., a hormone or neurotransmitter) and triggers a response by the cell. Receptors for water-soluble signals are transmembrane proteins in the plasma membrane; those for many lipid-soluble signals (e.g., steroid hormones) are located inside the cell.

Front 139

signal transduction

Back 139

The process by which a stimulus (e.g., a hormone, a neurotransmitter, or sensory information) outside a cell is amplified and converted into a response by the cell. Usually involves a specific sequence of molecular events, or signal transduction pathway.

Front 140

tight junction

Back 140

A type of cell-cell attachment structure that links the plasma membranes of adjacent animal cells, forming a barrier that restricts movement of substances in the space between the cells. Most abundant in epithelia (e.g., the intestinal lining). Compare with desmosome and gap junction.

Front 141

alcohol fermentation

Back 141

Catabolic pathway in which pyruvate produced by glycolysis is converted to ethanol in the absence of oxygen.

Front 142

anabolic pathway

Back 142

Any set of chemical reactions that synthesizes larger molecules from smaller ones. Generally requires an input of energy. Compare with catabolic pathway.

Front 143

chemiosmosis

Back 143

An energetic coupling mechanism whereby energy stored in an electrochemical proton gradient (proton-motive force) is used to drive an energy-requiring process such as production of ATP.

Front 144

citric acid cycle (book definition)

Back 144

A series of eight chemical reactions that starts with citrate (citric acid, when protonated) and ends with oxaloacetate, which reacts with acetyl CoA to form citrate—forming a cycle that is part of the pathway that oxidizes glucose to CO2. Also known as the Krebs cycle, tricarboxylic acid cycle, and TCA cycle.

Front 145

coenzyme A

Back 145

A nonprotein molecule that is required for many cellular reactions involving transfer of acetyl groups (–COCH3).

Front 146

coenzyme Q

Back 146

A nonprotein molecule that shuttles electrons between membrane-bound complexes in the mitochondrial electron transport chain. Also called ubiquinone or Q.

Front 147

cytochrome

Back 147

A soluble iron-containing protein that shuttles electrons between membrane-bound complexes in the mitochondrial electron transport chain.

Front 148

energetic coupling

Back 148

In cellular metabolism, the mechanism by which energy released from an exergonic reaction (commonly, hydrolysis of ATP) is used to drive an endergonic reaction.

Front 149

exergonic

Back 149

Referring to a chemical reaction that can occur spontaneously, releasing heat and/or increasing entropy, and for which the Gibbs free-energy change (DG) < 0. Compare with endergonic.

Front 150

facultative anaerobe

Back 150

Any organism that can perform aerobic respiration when oxygen is available to serve as an electron acceptor but can switch to fermentation when it is not.

Front 151

FAD/FADH2

Back 151

Oxidized and reduced forms, respectively, of flavin adenine dinucleotide. A nonprotein electron carrier that functions in the citric acid cycle and oxidative phosphorylation.

Front 152

flavin adenine dinucleotide FAD/FADH_2

Back 152

Oxidized and reduced forms, respectively, of flavin adenine dinucleotide. A nonprotein electron carrier that functions in the Krebs cycle and oxidative phosphorylation.

Front 153

nicotinamide adenine dinucleotide (NADP+/NADP)

Back 153

Oxidized and reduced forms, respectively, of nicotinamide adenine dinucleotide. A nonprotein electron carrier that functions in many of the redox reactions of metabolism.

Front 154

absorption spectrum

Back 154

The amount of light of different wavelengths absorbed by a pigment. Usually depicted as a graph of light absorbed versus wavelength. Compare with action spectrum.

Front 155

action spectrum

Back 155

The relative effectiveness of different wavelengths of light in driving a light-dependent process such as photosynthesis. Usually depicted as a graph of some measure of the process versus wavelength. Compare with absorption spectrum

Front 156

antenna complex

Back 156

Part of a photosystem, containing an array of chlorophyll molecules and accessory pigments, that receives energy from light and directs the energy to a central reaction center during photosynthesis.

Front 157

autotroph

Back 157

Any organism that can synthesize reduced organic compounds from simple inorganic sources such as CO2 or CH4. Most plants and some bacteria and archaea are autotrophs. Also called primary producer. Compare with heterotroph.

Front 158

Calvin cycle/reactions

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In photosynthesis, the set of light-independent reactions that use NADPH and ATP formed in the light-dependent reactions to drive the fixation of atmospheric CO2 and reduction of the fixed carbon, ultimately producing sugars. Also called carbon fixation and light-independent reactions.

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carotenoid

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Any of a class of accessory pigments, found in chloroplasts, that absorb wavelengths of light not absorbed by chlorophyll; typically appear yellow, orange, or red. Includes carotenes and xanthophylls.

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chlorophyll

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Any of several closely related green pigments, found in chloroplasts and photosynthetic protists, that absorb light during photosynthesis.

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cyclic photophosphorylation

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Path of electron flow during the light-dependent reactions of photosynthesis in which photosystem I transfers excited electrons back to the electron transport chain of photosystem II, rather than to NADP+. Also called cyclic electron flow. Compare with Z scheme.

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electromagnetic spectrum

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The entire range of wavelengths of radiation extending from short wavelengths (high energy) to long wavelengths (low energy). Includes gamma rays, x-rays, ultraviolet, visible light, infrared, microwaves, and radio waves (from short to long wavelengths).

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ferredoxin

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In photosynthetic organisms, an iron- and sulfur-containing protein in the electron transport chain of photosystem I. Can transfer electrons to the enzyme NADP+ reductase, which catalyzes formation of NADPH.

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glyceraldehyde-3-phosphate (G3P)

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The phosphorylated three-carbon compound formed as the result of carbon fixation in the first step of the Calvin cycle.

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PEP carboxylase

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An enzyme that catalyzes addition of CO2 to phosphoenol pyruvate, a three-carbon compound, forming a four-carbon organic acid. Found in mesophyll cells of plants that perform C4 photosynthesis.

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pheophytin

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In photosystem II, a molecule that accepts excited electrons from a reaction center chlorophyll and passes them to an electron transport chain.

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photorespiration

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A series of light-driven chemical reactions that consumes oxygen and releases carbon dioxide, basically reversing photosynthesis. Usually occurs when there are high O2 and low CO2 concentrations inside plant cells, often in bright, hot, dry environments when stomata must be kept closed.

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photosynthesis

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The complex biological process that converts the energy of light into chemical energy stored in glucose and other organic molecules. Occurs in plants, algae, and some bacteria.

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photosystem

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One of two types of units, consisting of a central reaction center surrounded by antenna complexes, that is responsible for the light-dependent reactions of photosynthesis.

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photosystem II

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A photosystem that contains a pair of P680 chlorophyll molecules and uses absorbed light energy to split water into protons and oxygen and to produce ATP.

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pigment

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Any molecule that absorbs certain wavelengths of visible light and reflects or transmits other wavelengths.

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plastocyanin

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A small protein that shuttles electrons from photosystem II to photosystem I during photosynthesis.

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plastoquinone

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A nonprotein electron carrier in the chloroplast electron transport chain. Receives excited electrons from pheophytin and passes them to more electronegative molecules in the chain. Also carries protons to the lumen side of the thylakoid membrane, generating a proton-motive force.

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ribulose biphosphate (RuBP)

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A five-carbon compound that combines with CO2 in the first step of the Calvin cycle during photosynthesis.

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rubisco

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The enzyme that catalyzes the first step of the Calvin cycle during photosynthesis: the addition of a molecule of CO2 to ribulose bisphosphate. Also called ribulose 1,5-bisphosphate carboxylase/oxygenase.

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visible light

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The range of wavelengths of electromagnetic radiation that humans can see, from about 400 to 700 nanometers.

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Z scheme

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Path of electron flow in which electrons pass from photosystem II to photosystem I and ultimately to NADP+ during the light-dependent reactions of photosynthesis. Also called noncyclic electron flow.