GEN BIO 1.3 Flashcards
THE LIFE OF A CELL
CELL CYCLE
series of events that takes place in a cell as it grows and divides.
CELL CYCLE
Highly regulated process
CELL CYLE
TWO MAJOR PHASES OF CELL CYCLE
interphase and mitotic phase (M-phase)
cells undergoes normal growth processes and there is a replication of DNA and other organelles .
INTERPHASE
cell spends most of its
time
LONGEST PHASE
the cell is at rest but metabolically active
RESTING PHASE
The largest phase in which 95% of
growth occurs
INTERPHASE
This is the time between cell
divisions
INTERPHASE
The cell is growing, copying itβs
DNA and preparing for division
INTERPHASE
The copying of DNA is called
SYNTHESIS OR REPLICATION
Before the cell moves from interphase to mitotic phase, there is a series of cell _________ to ensure that every component of the cell must meet the needed requirements
CHECKPOINTS
THREE STAGES OF INTERPHASE
- G1 (Gap1 Phase/ Growth 1 phase)
- S (Synthesis Phase)
- G2 (Gap2 Phase/ Growth 2 phase)
the cell increases in size, make new set of organelles, protein
synthesis
G1 PHASE
3 Major Checkpoints
- G1 checkpoint
- G2 checkpoint
- M-checkpoint
(metaphase checkpoint
or spindle checkpoint )
verify whether all the cellular activities are accurately completed at each stage of interphase
CELL CYCLE CHECKPOINTS
known as the restriction
point
CELL CYCLE CHECKPOINTS
is the main decision point for a cell β that is, the primary point at
which it must choose whether or not to divide.
G1 CHECKPOINT
first checkpoint which is located at the end of the cell cycleβs G1 phase
G1 CHECKPOINT
it is called a restriction point for animal cells and start point for yeast cells
G1 CHECKPOINT
- cellsβ size
- nutrients
- DNA integrity
- molecular signals
G1 CHECKPOINT
many cells stop at this stage and enter a resting state called G0
G1 CHECKPOINT
longest and the most essential
stage of interphase
SYNTHESIS PHASE
The cell replicates its DNA
SYNTHESIS PHASE
The cell continues to grow
and synthesize proteins while preparing for cell division.
G2 PHASE
It also checks for any DNA damage and repairs it to ensure that the cellβs genetic material is intact and
ready for division
G2 PHASE
Reorganize cell organelles
and DNA condensation
G2 PHASE
determine state of pre-mitotic
cell
G2 CHECKPOINT
ensure that all the chromosomes have been replicated and that the
replicated DNA is not damaged
G2 CHECKPOINT
identify a replication faults
G2 Checkpoint
the cell prepares for division and
checks for errors
G2 Checkpoint
DNA integrity and DNA replication
G2 Checkpoint
If the checkpoint mechanisms detect problems with the DNA, the cell cycle is halted, and the cell attempts to either complete DNA replication or repair the damaged DNA.
TRUE
If damage cannot be repaired, _______ or programmed cell
death occurs to ensure that the damage DNA is not passed on the daughter cells and important in preventing cancer.
APOPTOSIS
the cell undergoes different stages
namely prophase, metaphase, anaphase, and telophase. For every stage, there is a unique characteristic to distinguish one phase to another
MITOTIC PHASE
follows the mitosis phase, where
cytoplasm divides.
CYTOKINESIS
occurs near the end of the
metaphase stage of karyokinesis
M Checkpoint (metaphase checkpoint or spindle checkpoint)
ensure proper spindle assembly
and correct attachment to centromeres (prevents nondisjunction events)
M Checkpoint (metaphase checkpoint or spindle checkpoint)
If a chromosome is misplaced, the cell will pause mitosis,
allowing time for the spindle to
capture the stray chromosome.
M Checkpoint (metaphase checkpoint or spindle checkpoint)
It is a fundamental process to create life, occurring in all forms of it, ensuring the perpetuity of their existence, as well as growth,
tissue replacement/repair, and reproduction in multicellular organisms
CELL DIVISION
happens when a parent cell divides into two or more cells called daughter cells.
CELL DIVISION
Parent cells are diploid and make 2
daughter cells that are also diploid with their own new nuclei.
CELL DIVISION
________ means 2 of each chromosome: 2 (n)= 2 (23) = 46
chromosomes
DIPLOID
Living things grow because each cell increases in size.
FALSE because they grow by producing more cells
Cell division repairs damaged tissue
TRUE
If cell gets too big, it cannot get enough nutrients into the cell andwastes out ofthe cell
TRUE
located in the nucleus and controls all cell activities including cell
division
DNA
Long and thread-like DNA in
a non-dividing cell is called
chromatin
Doubled, coiled, short DNA
in a dividing cell is called
chromosome
Every organism has the same number of chromosomes.
FALSE because Every organism has its own specific number of
chromosomes.
All somatic (body) cells in an organism have the same kind and number of chromosomes
Examples:
* Human=46chromosomes
* Humanskincell =46 chromosomes
* Humanheart cell
* 46 chromosomes
* Human muscle cell = 46chromosomes
CHROMOSOME NUMBER
Many organisms, especially
unicellular organisms, reproduce
by means of cell division β called
asexual reproduction
BINARY FISSION
occurs in all the somatic (body) cells and is the process by which a single cell divides into two
MITOSIS (KARYOKINESIS)
Who discovered Mitosis?
Walther Flemming
Function:Growth and Repair, Cell reproduction
MITOSIS
phases of cell cycle
I Peed on the MAT. See?
Interphase > Prophase > Metaphase > Anaphase >Telophase > Cytokinesis
STAGES OF MITOSIS
- Early Prophase
- Mid Prophase
- Late Prophase
- Metaphase
- Anaphase
- Telophase
- Cytokinesis
Centrioles move to each pole of
the cell
EARLY PROPHASE
Chromosomes appear as long,
thin threads
EARLY PROPHASE
The nucleolus becomes less
distinct
EARLY PROPHASE
The nuclear membrane is still
visible
EARLY PROPHASE
Centrioles begin to organize
spindle fiber
MID PROPHASE
Sister chromatids are formed with a centromere as their point of attachment
MID PROPHASE
Centrioles are nearly at the
opposite sides of the nucleus
LATE PROPHASE
The nuclear membrane slowly
disintegrates
LATE PROPHASE
Chromosomes move toward the
equator
LATE PROPHASE
the chromatin in the nucleus condenses and coiled up into visible chromosomes, which become visible under a microscope.
MITOSIS: PROPHASE
The centrosome duplicates, and each one moves to one of the cellβs ends, where spindle fibers are formed.
MITOSIS: PROPHASE
Chromosomes can be seen as two
chromatids, inthe shape of an βXβ
PROPHASE
Nuclear envelope dissolves
PROPHASE
Centrioles are present with some
spindle fibers
PROPHASE
46 chromosomes
PROPHASE
The nuclear envelope /membrane breaks down, allowing the spindle fibers to attach to the chromosomes.
MITOSIS: PROPHASE
Chromosomes line up in middle of cell
MITOSIS: METAPHASE
Spindle fibers connect to chromosomes
MITOSIS: METAPHASE
The nuclear membrane has completely disappeared
MITOSIS: METAPHASE
The centromere of each double-stranded chromosome is attached to a spindle fiber at equator
MITOSIS: METAPHASE
Centrioles are already at opposite ends of the poles
MITOSIS: METAPHASE
The chromosomes line up at the center of the cell forming the metaphase plate
MITOSIS: METAPHASE
Chromosomes line up in the middle
METAPHASE
Nuclear envelope is gone (no
nucleus)
METAPHASE
Spindle fibers (on opposite poles)
are stretching towards the chromosomes
METAPHASE
46 chromosomes
METAPHASE
Chromosome copies divide and
moves to the opposite pole
MITOSIS: ANAPHASE
Spindle fibers pull chromosomes to
opposite poles
MITOSIS: ANAPHASE
Sister chromatids start to move
toward the poles, seemingly being
pulled by the thread or fibers
MITOSIS: ANAPHASE
Spindle fibers pull chromosomes
towards the separate poles
ANAPHASE
Chromosomes are split in HALF
ANAPHASE
Sister chromatids are now their OWN chromosome
ANAPHASE
The cell elongates due to action of the spindle fibers
ANAPHASE
92 chromosomes
ANAPHASE
Chromosomes uncoil
MITOSIS: TELOPHASE
Nuclear envelopes form
MITOSIS: TELOPHASE
2 new nuclei are formed
MITOSIS: TELOPHASE
Spindle fibers disappear
MITOSIS: TELOPHASE
Daughter chromosomes arrive at
the poles.
MITOSIS: TELOPHASE
The nuclear envelope reforms
around each set of chromosomes
(so daughter cells each have one)
and chromosomes straighten out
(uncoil)
TELOPHASE
Spindle fibers are gone
TELOPHASE
Cleavage furrow is forming
between the cells
TELOPHASE
46 chromosome
TELOPHASE
Final step in the Cell Cycle
CYTOKINESIS
Actually means βcell movingβ
CYTOKINESIS
The final pinching of the cell
into two complete identical
cells!
CYTOKINESIS
1 parent cell produced 2 daughter cells that are genetically identical
CYTOKINESIS
Chromosome Appearance & Location
DNA copies itself; chromatin
INTERPHASE
Important Events
DNA replication, cell grows and
replicates organelles
INTERPHASE
Chromosome Appearance & Location
Chromosomes coil up
PROPHASE
Important Events
Nuclear envelope disappears, spindle fibers form
PROPHASE
Chromosome Appearance
& Location
Chromosomes line up in the
middle
METAPHASE
Important Events
Spindle fibers connect to
chromosomes
METAPHASE
Chromosome Appearance
& Location
Chromosome copies divide
and move apart
ANAPHASE
Important Events
Spindle fibers pull chromosome copies apart to opposite poles
ANAPHASE
Chromosome Appearance & Location
Chromosomes uncoil back
into chromatin
TELOPHASE
Important Events
Nuclear envelopes reform, 2 new nuclei are formed, spindle fibers disappear
TELOPHASE
Chromosome Appearance & Location
Chromatin
CYTOKINESIS
Important Events
Division of the rest of the cell:
cytoplasm and organelles
CYTOKINESIS
The process of mitosis occurs in ______ from one cell to another.
VARIATION
They divide out of control forming growth that gives rise to tumors. Therapy restores checkpoint function and prevents uncontrolled cell growth in cancer cells.
CANCER CELLS
If certain enzymes and genes tell the cell cycle to begin too rapidly (proliferate), cell division becomes out of control (excessive
mitosis)
CANCER
When a _______ occurs,the cell loses a control to divide which leads to
development of cancer cells and eventually become disorder or
diseases
MUTATION
is a result from a pathophysiological response to external or internal factors.
DISEASE
is the gain or loss of whole chromosomes.It is the most common chromosome abnormality
ANEUPLOIDY
is disruption of the disease to the normal or regular functions in the body or a part of the body.
DISORDER
Disorder can be classified into
MENTAL
PHYSICAL
GENETIC
EMOTIONAL
BEHAVIORAL
STRUCTURAL
is a term that refers to a disease or a disorder that has more than one identifying feature or symptom
SYNDROME
is a well-known genetic syndrome.
DOWN SYNDROME
Medical syndromes can be caused by___________ or _____________.
GENETIC MUTATIONS OR OTHER FACTORS
is an abnormal state of health that interferes with the usual activities or feeling of wellbeing
CONDITION
is a disease that occurs when the cell cycle is no longer regulated. This may happen because a cellβs DNA becomes damaged.
CANCER
Cancerous cells generally
divide much faster than normal cells.
TRUE
are named for the area in which they begin and the type of cell they are made of, even if they spread to other parts of the body.
CANCERS
TYPES OF CANCER CELLS
CARCINOMA
SARCOMA
LEUKEMIA
is a cancer that starts in the skin or the tissues thatline other organs.
CARCINOMA
is a cancer of connective tissues such as bones, muscles, cartilage, and blood vessels.
SARCOMA
is a cancer of bone marrow, which
creates blood cells.
LEUKEMIA
failure of the chromosomes to separate, which produces daughter cells with abnormal numbers of
chromosomes.
NON-DISJUNCTION
Also known as trisomy 21
DOWN SYNDROME
flattened skull, pronounced folds of skin in the inner corners of the eyes, large tongue, and short stature,
DOWN SYNDROME
Also known as trisomy13
PATAU SYNDROME
The extra 13th chromosome
causes severe mental and physical
problems.
PATAU SYNDROME
Also known as trisomy 18
EDWARD SYNDROME
genetic condition that causes physical growth delays during fetal
development.
EDWARD SYNDROME
is a genetic condition that results when a boy is born with an extra copy of the X chromosome
KLINEFELTER
may adversely affect testicular growth, resulting in smaller than normal testicles, which can lead to lower production of testosterone. The syndrome may also cause reduced muscle mass, reduced
body and facial hair, and enlarged breast tissue. Men with this syndrome produce little or no sperm,
KLINEFELTER SYNDROME, XXY
occurs when one of the
X chromosomes is missing, either partially or completely
TURNER SYNDROME
often causes short stature, typically noticeable by age 5.
TURNER SYNDROME, XO
It usually doesnβt affect intelligence but can lead to developmental delays especially with calculations and memory. Heart problems are common, too. While TS can
somewhat shorten life expectancy,
screening for and treating known related conditions helps protect health.
TURNER SYNDROME, XO
Due to deletion of the terminal portion of chromosome 11q
PARISS-TROUSSEAU SYNDROME
cell division process where a single
(parent) cell divides twice to produce four independent (daughter) cells, each having half the chromosomes as the
original cell.
MEIOSIS
came from the Greek
word _______, meaning βlesseningβ
MEIOSIS
Discovered by Oscar Hertwig
MEIOSIS
takes place only in the reproductive cell types (sperm and egg
cells) of sexually reproducing organisms, including humans.
MEIOSIS
For a cell to undergo this cell division, it must have a diploid (2n) chromosome number.
MEIOSIS
Meiosis involves two successive stages or phases of cell
division __________ and _________
MEIOSIS I AND MEIOSIS II
Each stage includes a period of nuclear division or karyokinesis and a cytoplasmic division or cytokinesis
MEIOSIS
Although not a part of meiosis, the cells before entering meiosis I undergo a compulsory growth period called
INTERPHASE
PHASES OF MEIOSIS
MEIOSIS I
*Interphase I
*Prophase I
*Metaphase I
*Anaphase I
*Telophase I
*Cytokinesis I
MEIOSIS II
*Prophase II
*Metaphase II
*Anaphase II
*Telophase II
*Cytokinesis I
*Cell builds up energy
*DNA replicate
*Cell does not change
structurally
*Identical to
Interphase of Mitosis
INTERPHASE I
- longest phase of meiotic division
- most of the significant processes
of Meiosis occur here. - The duplicated chromosomes
condense, resembling an X-shaped
structure with two sister chromatids that become distinctly visible within the nucleus.
PROPHASE I
The homologous chromosome pair
(one inherited from each parent)
comes closer (create synapsis) and
associate along the entire chromosome length, forming a
tetrad. Each tetrad is composed of
four chromatids
PROPHASE I
Homologous chromosomes
exchange parts of DNA with each
other; this process is known as
crossing over
PROPHASE I
The points of physical contact
from which the genetic materials are exchanged are known as chiasmata.
PROPHASE I
- breakdown of the nuclear
envelope - Centrioles form and move
toward the opposite pole
PROPHASE I
exchange of genes between separate (non-sister) chromatids on homologous chromosomes
CROSSING OVER
leads to genetic recombination, which increases genetic diversity by producing new combinations of alleles in the resulting gametes (sperm or eggs).
CROSSING OVER
Homologous chromosomes
(bivalents) align along the
center of the cell
METAPHASE I
The centrioles reach the opposite poles of the cell with the spindle fibers extending from them.
METAPHASE I
Homologous chromosomes separate because of the
contraction of the spindle
fibers
ANAPHASE I
homologous chromosomes
start to migrate to the opposite poles.
ANAPHASE I
The chromosomes stop migrating (already at the pole) with each pole
containing a haploid number
of chromosomes.
TELOPHASE I
The nuclear envelope is formed, spindle fibers disappear and the chromosomes uncoil
TELOPHASE I
It involves the division of the cytoplasm to produce two
individual daughter cells each
with half the number of
chromosomes as the parent
cell (having 23 chromosomes
having 23 pairs of chromatids).
CYTOKINESIS I
Meiosis is thus also called the
reduction division.
CYTOKINESIS I
The nuclear membrane initiates to break down, and the spindle fibers appear again.
PROPHASE II
Each centrosome divides,
forming two pairs of centrioles
PROPHASE II
Chromatin condense into chromosome
PROPHASE II
Chromosomes arrange on the
equator of the cell with the help of
the spindle fibers.
METAPHASE II
The centrioles are now at opposite
poles in each of the daughter cells
METAPHASE II
Centromere divides, producing two
sister chromatids, now known as
daughter chromosomes, with the
spindle fibers attached to each
chromosome.
METAPHASE II
daughter chromosomes are
pulled towards the opposite
poles the help of the spindle
fibers
ANAPHASE II
each end of the cell contains
a complete set of chromosomes
ANAPHASE II
- Nuclear membrane forms
- Disappearance of the spindle fibers
- Nucleolus reappears
- Daughter chromosomes arrive at
the poles.
TELOPHASE II
- Identical to cytokinesis I
- involving the second cytoplasm
division, resulting in the
formation of two individual
daughter cells
CYTOKINESIS II
Thus at the end of meiosis II, ____ non-identical, ______ daughter cells are formed, each having ____ chromosome number
FOUR
HAPLOID
HALF
MEIOSIS I OR MEIOSIS II?
In ___________, a pair of homologous chromosomes separate to produce two diploid daughter cells, each
having half the number of chromosomes as the parent
cell.
MEIOSIS I
MEIOSIS I OR MEIOSIS II?
sister chromatids separate
to produce four haploid daughter cells. There is no genetic recombination by crossing over
occurs in ________.
MEIOSIS II
collection of mechanisms that
regulate the passage of solutes
such as ions and small molecules through cell/plasma membranes, which are lipid bilayers that contain proteins embedded in them
MEMBRANE TRANSPORT
The regulation of passage
through the membrane is due to
selective membrane permeability (semi-permeable)
MEMBRANE TRANSPORT
a characteristic of biological
membranes which allows them
to separate substances of
distinct chemical nature. In
other words, they can be
permeable to certain substances but not to others
MEMBRANE TRANSPORT
What if plasma membrane lost its
selective permeability?
The cell would have difficulty regulating the movement of
substances in and out, leading to problems with maintaining homeostasis and proper cellular function
process by which a cell or organism
maintains a stable internal environment despite changes in external conditions.
HOMEOSTASIS
THERE ARE TWO MAJOR WAYS IN WHICH MOLECULES OR PARTICLES CAN MOVE ACROSS A MEMBRANE
PASSIVE TRANSPORT
ACTIVE TRANSPORT
occurs when substances cross
the plasma membrane without
any input of energy from the cell.
PASSIVE TRANSPORT
Substances are moving from an
area where they have a higher
concentration to an area where
they have a lower concentration.
- It follows concentration gradient
PASSIVE TRANSPORT
3 TYPES OF PASSIVE TRANSPORT
- DIFFUSION
- FACILITATED DIFUSSION
- OSMOSIS
- random movement of
particles of a solute from a
region of high concentration
to low concentration
DIFFUSION
THREE MAIN FACTORS AFFECTING
THE RATE OF DIFFUSION
- concentration gradient
- temperature
- pressure
The higher the concentration,
temperature, and pressure, the
faster the rate of diffusion.
TRUE
Movement of the specific particles through specific carrier/ transport proteins situated in the
FACILITATED DIFFUSION
TYPES OF TRANSPORT PROTEIN
- CHANNEL PROTEINS
- CARRIER/TRANSPORT PROTEINS
These proteins form channels
or pores within the membrane, allowing ions or small polar molecules to move through them
CHANNEL PROTEINS
An example of a channel protein is
the ________, which facilitates
the movement of water molecules
across the membrane
AQUAPORIN
bind to specific molecules on
one side of the membrane and
undergo a conformational
change to transport the
molecule across the membrane
to the other side
CARRIER/TRANSPORTER PROTEINS
TYPE OF TRANSPORT PROTEIN
GLUCOSE TRANSPORTERS (GLUT PROTEINS)
What will happen if GLUT proteins
malfunction?
A malfunction in the carrier proteins responsible for glucose transport would limit the cellβs ability to take in
glucose, reducing the energy available for cellular processes and negatively impacting metabolism.
- diffusion of water across a
selectively permeable membrane - Water diffuses across a
membrane from the region of
lower solute concentration to the
region of higher solute
concentration until the solute
concentration is equal on both
sides.
OSMOSIS
vital to plant and animal cell
survival.
OSMOSIS
ability of a solution to cause a cell to gain or lose water
TONICITY
3 CLASSIFICATION OF TONICITY
*Hypotonic
*Hypertonic
*Isotonic
- The concentration of solutes
outside the cell is LESS than the
concentration solutes inside the
cell, thus water enters the cell. - Effects: Swell, burst, turgid,
cytolysis
HYPOTONIC
The concentration of solutes
outside the cell is GREATER
than the concentration solutes
inside the cell, thus water
leaves the cell.
- Effects: Shrink, Shrivel,
Plasmolysis
HYPERTONIC
The concentration of solutes outside the cell is EQUAL to the concentration of solutes inside the cell, water moves
equally in both direction.
- Effect: Normal, no change,
equilibrium
ISOTONIC
Is having more aquaporins better
considering osmosis?
Having more aquaporins generally improves the efficiency of osmosis. Aquaporins facilitate faster and more effective water movement across the cell membrane, helping the cell better regulate its water balance and adapt to changing
conditions
Cell use energy (with utilization of ATP or, in some cases, the electrochemical gradient created by ATPdriven pumps.
ACTIVE TRANSPORT
Movement of molecules from an area of low concentration to an area of high concentration (against
the concentration gradient)
ACTIVE TRANSPORT
2 TYPES OF ACTIVE TRANSPORT
- Primary Active Transport
- Secondary Active Transport
energy is DIRECTLY used to
transport molecules or ions
against their concentration
gradient.
PRIMARY ACTIVE TRANSPORT
typically achieved by
transmembrane proteins known
as pumps.
PRIMARY ACTIVE TRANSPORT
which actively transports sodium ions (Na+) out of the cell and potassium ions (K+) into the
cell. The pump uses energy from
the hydrolysis of ATP to move
these ions against their concentration gradients, maintaining the proper ion
balance and electrical potential
across the cell membrane
PRIMARY ACTIVE TRANSPORT
relies on the energy established
by primary active transport
(usually through the Na+/K+
pump) to transport other
molecules or ions.
SECONDARY ACTIVE TRANSPORT
TWO MAIN TYPES OF SECONDARY ACTIVE TRANSPORT
βͺ Symport (Cotransport)
βͺ Antiport (Counter
transport)
molecules or ions are transported in
the same direction across the
membrane. One molecule is moved
against its gradient while the other is moved with its gradient
Symport (Cotransport)
the sodium-glucose
cotransporter (SGLT) uses the
energy created by the sodium
gradient to transport glucose into
the cell against its concentration
gradient
SYMPORT (COTRANSPORT)
molecules or ions are transported
in opposite directions across the
membrane. As one molecule is
transported against its gradient
into the cell, another molecule is
transported out of the cell with its
gradient.
Antiport (Counter Transport)
The sodium-calcium exchanger
(NCX) is an example of an antiport
protein that uses the sodium
gradient to exchange sodium ions
for calcium ion
ANTIPORT (COUNTER TRANSPORT)
process by which large quantities of
materials, molecules, or even entire
structures are transported into or out of a cell through various cellular
mechanisms.
BULK TRANSPORT
plays a vital role in moving
macromolecules, organelles, and other large substances within and between cells.
BULK TRANSPORT
BULK TRANSPORT 2 TYPES
Endocytosis and Exocytosis
process by which a cell takes in
large particles or substances from
its external environment by
enclosing them in a vesicle
formed from the cell membrane.
ENDOCYTOSIS
3 TYPES OF ENDOCYTOSIS
PHAGOCYTOSIS
PINOCYTOSIS
RECEPTOR-MEDIATED ENDOCYTOSIS
- Cell eating
- cells engulf solid
particles thru extending pseudopods
PHAGOCYTOSIS
- Cell drinking
- involves the non-selective
uptake of small droplets of
extracellular fluid containing
dissolved solutes.
PINOCYTOSIS
specific molecules, usually
ligands, bind to receptor
proteins on the cell surface
RECEPTOR-MEDIATED ENDOCYTOSIS
essential for the uptake of
various molecules, including
hormones, enzymes, and
cholesterol
RECEPTOR-MEDIATED ENDOCYTOSIS
release of large molecules or
substances from a cell into the
extracellular space. This is typically
accomplished by merging secretory
vesicles containing the materials with the cell membrane, allowing their contents to be expelled outside the cell.
EXOCYTOSIS
*is crucial for the secretion of various substances
EXOCYTOSIS
