Cell Biology Exam 4 Evan Kaplan

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At any one time, a typical eukaryotic cell carries out...

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At any one time, a typical eukaryotic cell carries out...

thousands of different chemical reactions

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For a cell to operate effectively, the different intracellular processes that occur simultaneously ...

must somehow be segregated

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A method of cells isolating/organizing reactions is confining different metabolic processes within different membrane-enclosed compartments or ______________


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Prokaryotic cells usually consist of...

a single compartment enclosed by the plasma membrane

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Eukaryotic cells are sub-divided by ____________________

internal membranes

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The ____________ ______________ _____________ in eukaryotic cells are all distinct, each contain a unique set of large and small molecules that determine its specialized function

membrane-enclosed organelles

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Organelles occupy nearly __________ the volume of a eukaryotic cell


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In a typical mammalian cell, the area of the endoplasmic reticulum membrane is ______________ than that of the plasma membrane

20-30 times greater

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In terms of area and mass, the plasma membrane is only a _____________ ________________ in most eukaryotic cells

minor membrane

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Each organelle obtains its ___________ from the _____________, where they are made, to the compartment where they are used

proteins, cytosol

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Proteins are being produced _________________


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Newly made proteins must be accurately delivered to their ______________ ______________, where they will perform their function

appropriate organelle

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Directing new proteins to _____________________________ is necessary for any cell to grow, divide, and function properly

their correct organelle

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For the interior of the ___________ , __________ , ___________ , ___________ , and ____________ , proteins are delivered directly from the cytosol

nucleus, mitochondria, chloroplasts, peroxisomes, and ER

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For the ER, some proteins ________________________ but most are ____________________

stay there, transported by vesicles to the Golgi and then onward to other organelles/the plasma membrane

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The _______________ and _______________ also make some of their proteins

mitochondria and chloroplasts

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The synthesis of most proteins in the cell begins at....

ribosomes located in the cytosol

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_______________ ________________ is the process of transporting a protein to its destination where it will function

Protein sorting

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A particular segment of the proteins' amino acid sequence will act as a ________________ _______________ that is involved in directing the protein to a particular organelle/location

sorting signal

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____________ _____________ ______________ direct the movement of (or sort) proteins. They are comprised of a continuous stretch of 15-60 __________ ___________ long.

sorting signal sequences, amino acids

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Removal of a signal sequence from an ER protein...

converts it to a cytosolic protein

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Addition of a signal sequence to a cytosolic protein...

converts it to an ER protein

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A protein that lacks a sorting signal will...

remain and function in the cytosol

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_______________ _________________ are another form of targeting proteins to specific locations; never removed; commonly used for directing proteins to the nucleus

signal patches

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Signal patches are made up of amino acids that are _______________ to one another in the primary sequence, but _______________ to each other in the tertiary structure of the folded protein

distant, come closer

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Proteins are transported throughout the cells by various mechanisms:

- Through nuclear pores

- Across organelle membranes

- By transport vesicles

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Proteins transported to the interior of nucleus are completely synthesized in the cytosol and _____________ before import.

correctly folded into its three dimensional structure

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___________ _____________ are physical holes in the nuclear membrane that molecules travel through

nuclear pores

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Nuclear pores function as ____________ ______________ that actively transport specific macromolecules, but allow free diffusion of smaller molecules

selective gates

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The __________ ___________ , which encloses the nuclear DNA and defines the nuclear compartment is formed from two membranes

nuclear envelope

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Inner nuclear membrane

contain proteins that act as anchoring sites for the chromosomes and contains the nuclear lamina (that provides structural support)

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Outer nuclear membrane

closely resembles the membrane of the ER and is continuous with it

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Traffic flow into the nucleus:

newly made proteins enter from the cytosol

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Traffic flow out of the nucleus:

RNA molecules synthesized in the nucleus and ribosomal subunits assembled in the nucleus

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Larger molecules/macromolecules cannot easily ____________________ to enter and exit the nucleus

pass through

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Proteins will have a sorting signal sequence called a ________________ _______________ ________________ that directs large molecules from the cytosol into the nucleus

nuclear localization signal

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The nuclear localization signal region of the protein is recognized by cytosolic proteins called ___________ _____________ ____________ which bind to the signal and help direct the protein from the cytosol to the nuclear pore

nuclear import receptors

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Ribosomal subunits that are transported out of the nucleus are __________________ , before transport

assembled first

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Protein transport from the cytosol into the ER, mitochondria, chloroplasts, and some peroxisomes occurs via special transport proteins called _____________


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Translocator proteins form ______________ _________________ through the membrane; proteins then travel across the membrane through these in an unfolded state

translocator channels

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Proteins targeted to mitochondria and chloroplasts usually have a signal sequence at the ________________ (the end synthesized first) that contains both hydrophobic and positively charged amino acids


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The signal sequence on the N-terminus is recognized by specific proteins attached to the organelle membrane, called ______________ _______________

import receptors

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The import receptors then associate with _____________ ______________ embedded in the membrane

protein translocators

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Proteins are translocated ___________________ across both the inner and outer membranes at specialized sites where the two membranes contact each other


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Each protein is ____________ as it is transported and its signal sequence is _____________ after translocation is complete

unfolded, removed

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Additional proteins called ______________ _______________ aid in the transport of the protein across the two membranes and help fold it back into its tertiary structure once inside

chaperone proteins

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________________ also need to be transported to the mitochondria and chloroplasts to maintain their membranes; mechanism not fully understood


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Most of the membrane phospholipids from lipids are thought to be imported from the _____________ ER, which is the main site of lipid _______________

smooth, synthesis

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Phospholipids are transported to these organelles by

______________ ______________ _________________ that extract a phospholipid molecule from one membrane and deliver it to another; believed to occur at specific junctions where mitochondrial and smooth ER membranes are held in ______________

lipid carrying proteins, close proximity

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______________________ small, membrane bound organelles that contain several enzymes that produce hydrogen peroxide and have a variety of functions (break down a variety of molecules, including toxins, alcohol, fatty acids; synthesize certain phospholipids)


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Peroxisomes can be derived from the ___________ ___________ and/or replicate by ______________

smooth ER, fission

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Peroxisomes get most of their proteins from...

ribosomes in the cytosol

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Transport of proteins synthesized in the ER move via ____________ _____________ through the secretory pathway, from ER to Golgi to cell surface/lysosomes.

vesicular transport

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________________ ________________ become loaded with proteins from internal space of appropriate organelle; pinch off from the membrane of one organelle and fuse with the membrane of the second

transport vesicles

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The ER is the most _____________ membrane system in the cell; serves as the entry point for proteins destined for other organelles as well as the ER itself


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Two kinds of proteins transported from the cytosol:

Water-Soluble (completely translocated across the membrane and enter ER lumen) and Prospective Transmembrane (partially translocated across the ER membrane and become embedded in it)

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Proteins destined (via vesicles) for the Golgi apparatus and lysosomes, as well as proteins destined for the cell surface...

all first enter the ER from the cytosol

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Proteins are imported into the ER during ___________


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The elongation of each ___________________ provides the push needed to push the growing chain through the ER membrane


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The _____________________ and _______________________ help guide ER signal sequences to the ER membrane

signal recognition particle (SRP) and SRP receptor

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The ____________________ binds to the SRP receptor in the ER membrane and docks with the protein translocator channel

SRP-ribosome complex

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Some proteins made in the ER are destined to function in the ER; some proteins remain embedded in the ER membrane as _____________ _____________

transmembrane proteins

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In most cases, they are retained in the ER by a C-terminal sequence of 4 amino acids called an _______ _______________ ________________. This signal is recognized by a membrane bound receptor protein in the ER.

ER retention signal

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_____________________ is the first step in a protein's pathway to its target location

entry into the ER

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Vesicular transport in eukaryotic cells depends on...

specific sets of proteins involved in the sequential steps of vesicle budding, uncoating, tethering/docking to the target membrane, as well as in membrane fusion and cargo release.

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Vesicles form by ______________ from membranes of ER, Golgi, and the plasma membrane


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Each bud has a distinctive coat protein on the cytosolic surface called ___________ ___________;

coated vesicles

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The coat protein helps shape the membrane into a __________ that captures the specific molecules for outward transport that carry specific transport signals that are recognized by cargo receptors in the Golgi or plasma membrane


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After budding, the protein coat is lost (called ___________) and the vesicle is ready for transport


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The transport of vesicles can occur over short or long distances:

short- by diffusion

long- cytoskeleton based motor proteins

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Tethering/docking of vesicle to its target membrane is specific and involves...

specific proteins

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Once the vesicle and the target membranes are docked, several other proteins join to form a _________ ____________ , that results in the fusion of the vesicle with the target membrane.

fusion complex

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Cell signaling

the process of cells detecting and responding to signals in the extracellular environment

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Cells must be able to ____________________ to coordinate their activities

interpret signals

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Cells most often communicate by __________ __________, although signal make take other forms

chemical signals

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Other forms of signals:

-signal molecules can be in the form of proteins, amino acids, nucleotides, steroids, fatty acids, and gases

-physical/environmental signals such as light, temperature, and pressure (generally converted to chemical signals)

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___________ ____________ ____________ are comprised of a series of molecules or signals in which one acts upon another, which acts on another, and so forth

signal transduction pathways

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A signal transduction pathway typically starts with a physical/environmental signal or signaling cell that produces a particular type of ___________ ___________ __________

extracellular signal molecule

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The signal molecule is able to act upon another cell (or the original cell) called the ______________ by binding to special proteins called ______________

target cell, receptors

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Three stages of signal transduction


-signal transduction

-cellular response

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______________ is when a extracellular signal molecule (or ligand) binds to a receptor


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_____________ ______________ is the transfer of signal from outside to inside of cell (not necessarily transduction of ligand, often multi-stepped)

signal transduction

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____________ _____________ is when response is initiated and/or occurs entirely within receiving cell (alters the cell's shape, movement, or metabolism; or changes in gene expression)

cellular response

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Long distance signaling that is able to signal the entire body, very often occurs through systemic circulation, involves chemical signals called hormones

endocrine signaling

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The hormones are released into the ____________ and bind to receptors in target cells located far away from the signaling cell


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A certain type of cell will release the signal and a different type of cell will respond to the signal, signal does not affect originating cell, but influences those nearby (neighboring cells)

paracrine signaling

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Form of paracrine, a certain type of cell will release the signal and the SAME cell will response to the signal


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"Direct intercellular signaling", involves neurons delivering messages across long distances, delivery is quick and specific for individual target cells, able to convert electrical impulses to chemical and vice versa

neuronal signaling

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Chemical signals in neuronal signaling are called _________________


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Occurs between cells that are in direct contact with each other, signal is never released into the extracellular space, the two cells kind of "hold hands" (they muct be adjacent and in direct contact with one another)

contact-dependent signaling

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In order for a cell to _____________ to a signal, the cell must have a ________________ for it.

respond, receptor

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A ______________ is a protein molecule usually found inside or on the surface of a cell, that receives chemical signals from the outside


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Each receptor is usually activated by...

only one type of signal

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The signal from the receptor is then conveyed onto the _________________ via a set of intracellular signaling molecules

target cell interior

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The same ________________ can induce different ______________ in different target cells

signal molecule, responses

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A cell will have many different types of receptors and _________________________ of copies of each one; allows cells to be sensitive to many signals

hundreds to thousands

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Receptors relay signals from the outside to the inside via ___________ _______________ ______________

intracellular signaling pathways

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Steps of intracellular signaling pathway

- extracellular signal sent from a cell

- receptor protein (on the target cell) receives external signal and generates a new intracellular signal response

- intracellular signaling molecules pass the intracellular signal down a chain of intracellular signaling molecules

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The components of an intracellular signaling pathway can perform a variety of functions:

- transforms the signal into an intracellular molecular form

- relays the signal from the signal entry site to the response site

- can amplify the signal received, making it stronger and resulting in a larger intracellular response

- integrates them before relaying and/or distributes the intracellular signal to various other signaling proteins

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Reasons why we have a relay system:

- multiple steps in the relay can either make the signal stronger/louder or softer/quieter in a quick manner

- provides more accurate and specific control (fine tuning)

- more variability in response from cell to cell

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