MOD 2 Flashcards
is a series of events which describes the sequence of activities as a cell prepares to divide and then does.
A cell cycle
Cell cycle rate varies in different tissues at different times.
Some cells continue dividing even after a person die.
Frequent mitosis enables the embryo and fetus to grow rapidly.
By birth, the mitotic rate slows dramatically.
Later on, mitosis maintains the numbers and positions of specialized cells in tissues and organs
Cell cycle
The cell cycle is ______, but we describe it with stages.
continual
The two major stages are
interphase (not dividing) & mitosis (dividing)
In ________, a cell duplicates its chromosomes.
mitosis
In _________, it apportions one set of chromosomes into each of two resulting cells, called daughter cells.
The division maintains the set of 23 chromosome pairs characteristic of a human somatic cell.
cytokinesis
Another form of cell division, ____________, produces sperm or eggs, which have half the amount of genetic material in somatic cells, as 23 single chromosomes.
meiosis
is divided into two gap phases (G1 and G2) & one synthesis phase (S).
Interphase
cell can exit the cell cycle at G1 to enter a ____________ called G0.
A cell in G0 phase, maintains its specialized characteristics but does not replicate its DNA or divide.
From G0, a cell may also proceed to mitosis and divide, or die
quiet phase
______ may ensure if the cell’s DNA is so damaged that cancer might result.
Apoptosis
______ then is when a cell’s fate is either decided or put on hold
G0
__ is the period of the cell cycle that varies the most in duration among different cell types.
Slowly dividing cells, like liver cells, may exit at G1 & enter G0 where they remain for years.
Rapidly dividing cells in the bone marrow sped through G1 in 16-24 hours.
Cells of the early embryo may skip G1 phase entirely
G1
During ____, the cell replicates its entire genome.
As a result, each chromosome then consists of two copies joined at an area called the centromere.
S phase
In most human cells, S phase takes _____ hours.
Many proteins are synthesized during this phase, including those that form the mitotic spindle that will pull the chromosomes apart.
8-10
Microtubules form structures called _________ near the nucleus.
Centriole microtubules join with other proteins and are oriented at right angles to each other, forming paired, oblong structures called centrosomes that organize other microtubules into the spindle.
centrioles
_____ occurs after the DNA has been replicated but before mitosis begins.
More proteins are synthesized during this phase.
Membranes are assembled from molecules made during G1 and are stored as small, empty vesicles beneath the plasma membrane.
These vesicles will merge with the plasma membrane to enclose the 2 new daughter cells.
G2
As _______ begins, the replicated chromosomes are condensed enough to be visible, when stained, under a microscope.
mitosis
The 2 long strands of identical chromosomal material in a replicated
chromosome are called _______, and the space between them is a
_______
chromatids, furrow
When and where a somatic cell divides is crucial to health.
Illness can result from abnormally regulated mitosis.
Too little mitosis, and an injury goes unrepaired;
Too much, & an abnormal growth forms.
CONTROL OF CELL CYCLE
Groups of interacting proteins function at specific times in the cell cycle called ________ to ensure that
chromosomes are faithfully replicated and apportioned into daughter cells.
checkpoints
- temporarily pauses the cell cycle while special proteins repair damaged DNA.
DNA damage checkpoint
– turns on as mitosis begins. Proteins called survivins override signals telling the cell to die, ensuring that mitosis (division) rather than apoptosis (death) occurs.
Apoptosis checkpoint
– oversees construction of the spindle & the binding of chromosomes to it.
Spindle assembly checkpoint
Cells obey an internal clock that tells them approximately how many times to divide.
The mitotic clock ticks down with time.
Cells know how many divisions remain through the chromosome tips called _________.
__________ function like cellular fuses that burn down as pieces are lost from the ends. At each mitosis, _________ lose bases, gradually shortening the chromosome.
telomeres, Telomeres,telomeres
After about a critical length of telomere DNA is lost, it would signal mitosis to stop.
The cell may remain alive but not divide again, or it may die.
Not all cells have shortening telomeres.
In egg cells, sperm cells, cancer cells, bone marrow cells, they have an enzyme called __________ which keeps chromosome tips long.
telomerase
_________ rapidly & neatly dismantles a cell into membrane-enclosed pieces
that a phagocyte (a cell that engulfs and destroys another) can mop up.
_________ is also a continuous process.
It begins when a “death receptor” on the cell’s plasma membrane receives a signal to die.
Within seconds, enzymes called ________ are activated inside the doomed cell, stimulating each other
and snipping apart various cell components.
Apoptosis, Apoptosis, caspases
Steps in apoptosis
-Normal cell
- the cell shrinks chromatin condenses
-membranes start blebbing organelles disentegrate
- Nucleus and organelles collapse membrane continues to bleb
- Apoptopic bodies form
- macrophages phagocytose apoptotic bodies
_________ and ______________ renew tissues so that as the body grows, or loses cells to apoptosis, injury, and disease, other cells are produced that take their places.
Stem cells, progenitor cells
A stem cell divides by ______ to yield EITHER 2 daughter stem cells like
itself, or one stem cell and one progenitor cell
mitosis
Stem cells provide raw material for producing specialized cells, while retaining nathe ability to generate new cells. Ex. a ____________ stem cell in the bone
marrow produces progenitors whose daughter cells are specialized blood cells.
hematopoietic
_____________ is what makes a stem cell a stem cell – its ability to continue the
lineage of cells that can divide to give rise to another cell like itself.
Self-renewal
A ___________ cell CANNOT self-renew, and its daughter cells specialize as any of a restricted
number of cell types.
progenitor
Stem cells & progenitor cells are described in terms of developmental potential:
_____________ – which means it can give rise to every cell type, including the
cells of the membranes that support the embryo.
______________ – their daughter cells have fewer possible fates
______________ – daughter cells have only a few developmental choices.
Totipotent
Pluripotent
Multipotent
