Biology Ch 11

Why does a cell divide rather than continuing to grow?

Why does a cell divide rather than continuing to grow?

the larger a cell becomes, the less efficient it is in moving materials across its cell membrane and places increasing demand on its own DNA

to stay alive, a cell must…

allow food, oxygen, and water to enter and waste products to leave through its cell membrane

the rate at which materials enter and leave the cell depends on the cell’s

surface area

surface area and volume _______ increase at the same rate

do not

equation of surface area

l * w * number of sides

equation of volume

l * w * h

what problem does the decrease in surface area cause for a growing cell? how is this problem solved?

causes a decrease in relative amount of cell membrane available which creates serious problems, solved by using unusual shapes or structures to maintain the ratio

if a cell were to get too large

it would be more difficult to get sufficient amounts of oxygen and nutrients in and waste products out

living cells store critical information in a molecule known as

DNA

what is use of DNA as a cell grows?

the critical information inside DNA is used to build molecules needed for cell growth

as a cell increases in size, what happens to its DNA?

remains the same so it needs to be duplicated and divided between two new cells

cell division

process by which a cell divides into two new daughter cells

before cell division can occur, what needs to happen?

DNA has to be copied or replicated

what problem does cell division solve and how?

the problem of increasing size by reducing cell volume resulting in an increase in the ratio of surface area to volume for each daughter cell allowing for more efficient exchange of materials

for many single celled organisms, _______ is their only form of reproduction

cell division

aesexual reproduction

production of genetically identical offspring from a single parent

sexual reproduction

production of offspring through the fusion of two reproductive cells formed by each of two parents, inheriting some of their genetic information from each parent

pros and cons of asexual reproduction

pros: reproduce quickly

cons: lack of genetic diversity

pros and cons of sexual reproduction

pros: genetic diversity which increases chances of survival during environment changes

cons: relies on finding a mate

chromosomes

packages of DNA in which genetic information is bundled

where is all or most of a cell’s genetic information found in prokaryotes?

in a singular DNA chromosome in the cytoplasm

chromatin

complex of DNA tightly bound to proteins known as histones in eukaryotes

nucleosomes

beadlike structures formed when DNA tightly coils around histone molecules

why do cells package their DNA into chromosomes?

to ensure equal division of DNA when a cell divides

chromosomes are precisely separated into two ________ during cell division

daughter cells

cell cycle

series of events during which a cell grows, prepares for division, and then divides to form two daughter cells

after the cell cycle, each daughter cell moves into a new cell cycle of ….

activity, growth, and division

the process of cell division in prokaryotes is a form of asexual reproduction known as’

binary fission

what happens during prokaryotic cell cycle?

chromosome is replicated, two DNA molecules attach to different regions of cell membrane, a network of fibers stretch from one side of the cell to the other and the cell is pinched inward, dividing the cytoplasm and chromosomes between two newly formed cells

four stages of the eukaryotic cell cycle

G1: cell growth, S: DNA replication, G2: preparing for cell division, M Phase: cell division

interphase

the in between period of growth (consists of the phases G1, S, and G2)

what happens in the G1 phase?

cells increase in size and synthesize new proteins and organelles

what happens in the S phase?

new DNA is synthesised as the chromosomes are replicated

what happens in the G2 phase?

many of the organelles and molecules required for cell division are produced

what happens in the M phase?

two daughter cells are produced in two stages

what are the two stages of the M phase?

mitosis and cytokinesis

mitosis

division of the cell nucleus

cytokinesis

division of the cytoplasm

four stages of mitosis

prophase, metaphase, anaphase, and telophase

prophase

genetic material inside the nucleus condenses and the duplicated chromosomes become visible

during prophase, each duplicated chromosome condenses to appear as two thick strands known as

sister chromatids

sister chromatids are attached at a point called

centromere

centrioles

tiny paired structures located in the centrosome where spindle fibers extend from

plant cells lack

centrioles

metaphase

centromeres of the duplicated chromosomes line up across the center of the cell and spindle fibers connect the centromere of each chromosome to the poles of the spindle

anaphase

chromosomes separate and move along spindle fibers to opposite ends of the cell, microtubules disassemble as chromosomes move toward the poles of the mitotic spindle

telophase

chromosomes begin to spread out into a tangle of chromatin and a nuclear envelope reforms around each cluster of chromosomes and gradually a nucleolus becomes visible in each daughter nucleus

cytokinesis completes the process of cell division by

dividing one cell into two

cytokinesis in animal cells

cell membrane is drawn inward until the cytoplasm is pinched into two nearly equal parts each containing its own nucleus and cytoplasmic organelles

cytokinesis in plant cells

cell plate forms halfway between the divided nuclei and develops into cell membranes that separate the two daughter cells (since rigid cell wall is not flexible enough to be drawn inward)

what happens during the healing process?

cells divide rapidly until they come in contact with other cells

The cell cycle is controlled by…

Regulatory proteins both inside and outside the cell

Internal regulatory proteins

Respond to events inside the cell and act as checkpoints that allow the cell cycle to proceed

External regulators proteins

Proteins that respond to outside events that direct cells to speed up or slow down the cell cycle; prevent excessive cell growth and keeps body tissues from disrupting one another

Growth factors

An important group of external regulatory proteins that stimulate the growth and division of cells

cyclin

a protein that forms mitotic spindle when injected into a non dividing cell; seems to regulate the cell cycle

what happens to the cyclin concentrations during the cell cycle?

the levels increase during the G1, S, and G2 phases and decrease during the M phase

apoptosis

a process of programmed cell death

what happens during apoptosis?

cell and its chromatin shrink then parts of the cell’s membranes break off; neighbouring cells clean up the cell’s remains

why is apoptosis important?

it shapes the stucture of tissues and organs

what happens when apoptosis does not occur?

a number of diseases can result (ex: AIDS, Parkinsons)

cancer

disorder in which body cells lose the ability to control growth

why do cancer cells grow uncontrollably?

they do not respond to the signals that regulate the growth of most cells; the cell cycle is then disrupted and cells grow and divide uncontrollably

tumor

a mass formed from cancer cells

what happens as cancer cells spread to surrounding healthy tissue?

they absorb the nutrients needed by other cells, block nerve connections, and prevent the organs they invade from functioning properly

what causes cancer?

defects in the genes that regulate cell growth and division

what do all cancers have in common?

the control over the cell cycle has broken down (some cancer cells stop responding to external growth regulators and others fail to produce internal regulators)

why are cancer cells so dangerous?

because of their tendency to spread once they enter the bloodstream or lymph vessels and can then make tumors in other parts of the body

metastasis

the process of cancer moving into other parts of the body and forming secondary tumors

what are the treatments for cancer?

surgical removal of tumors, carefully targeted beams of radiation, or chemotherapy

what is the problem with chemotherapy?

it can interfere with cell division in normal healthy cells

embryo

a developmental stage from which the adult organisms gradually produced

what happens during the developmental process?

cells become more and more different from one another and specialized for particular functions

differentiation

process by which cells become specialized into one of many distinct cell types

when can an adult cell no longer turn into other types of cells?

when differentiation is completely

zygote

fertilised egg from which all the differentiated cell types are formed; totipotent

totipotent

able to develop into any type of cell in the body

blastocyst

hollow ball of cells with a cluster of cells inside (the inner cell mass); pluripotent

pluripotent

able to develop into any of the body’s cell types but cannot from tissues around the embryo

stem cells

unspecialised cells from which differentiated cells develop

adult stem cells

produce new cells for tissues like blood and skin that have a limited life span and need to be replaced; mutltipotent

multipotent

can form differentiated cells only when replacing cells in tissues where they are found

how do embryonic and adult stem cells differ?

embryonic stem cells are more versatile since they pluripotent while adult stem cells are multipoint

what are the ethical issues with stem cell research?

to study embryonic stem cells an embryo needs be destroyed

why is stem cell research important?

might be used in the future to repair the damage caused by a heart attack

what are iPS cells?

cells that closely resemble embryonic stem cells

how are iPS cells produced?

under a set of precise conditions that can reprogram an entire cell and put it back into an embryonic state

regenerative medicine

makes use of stem cells to repair or replace damaged cells and tissues

how is regenerative medicine useful?

the produced differentiated cells can repair or replace damaged or diseased cells, tissues or even whole organs

what are the risks of regenerative medicine?

transplanted cells may behave in unpredicted ways and could differentiate into unwanted cell types, spread beyond the site of the transplant, or grow uncontrollably into a tutor