Honors Biology Ch 10 test!!!!!
Terms in this set (53)
The process by which a cell divides into two new daughter cells.
-Before a cell becomes too large, a cell divides into two "daughter" cells. Before cell division occurs, the cell replicates, or copies all of its DNA. This solves the problem of information "overload" because each daughter cell gets one complete copy of genetic information. Cell division also solves the problem of increasing size by reducing cell volume. Cell division results in an increase in the ratio of SA to V for each daughter cell. This allows for the efficient exchange of materials within a cell.
The production of genetically identical offspring from a single parent.
-mostly single celled organisms but some multicellular organisms do it also
-process can be relatively simple, efficient, and effective, enabling populations to increase in number very quickly.
animal-hydra plant-Kalanchoe, and bacteria
Involves the fusion of two separate parent cells. Offspring inherit some of their genetic information from each parent.
-mostly multicellular organisms but some single celled organisms do it also.
-most animals and plants reproduce sexually
What is information "Overload"?
As a cell increases in size, its DNA does not, so if a cell were to grow too large, an "information crisis" would occur because not enough DNA is there for the growing cell.
-Library analogy-small town with a library and as the town grows, more people borrow books , so people may have to wait to borrow popular books. Similarly, a larger cell would make greater demands on its genetic "library". After a while, the DNA would no longer be able to serve the needs of the growing cell-may be time to build a new library.
How is exchanging materials in the cell affected from cellular growth?
Food, water, and oxygen enter a cell through its cell membrane and waste products leave a cell in the same way. The rate at which this exchange takes place depends on the surface area of the cell (total area of its cell membrane). The rate at which food and oxygen are used up and waste products are produced depends on the cell's volume. The greater the cell is, the less efficient it is in moving nutrients and waste materials across the membrane. (Volume increases faster than surface area, so the exchange across the membrane will get jammed and slowed down. And the bigger the cell, increased need for nutrients and more waste products produced)
What are some of the difficulties a cell faces as it increases in size?
The larger a cell becomes, the more demands the cell places on its DNA. In addition, a larger cell is less efficient in moving nutrients and waste materials across the cell membrane.
Formula for surface area and volume
-length x width x number of sides-->SA
-length x width x height-->V
-Surface are does not increase as fast as volume increases
Town Analogy- Suppose a town had a two-lane main street leading to the center of the town. As the town grows, more and more traffic clogs the main street. Becomes increasingly difficult to move goods in and out. A cell that continues to grow would experience similar problems. If a cell got too large, it would be more difficult to get sufficient amounts of oxygen and nutrients in and waste products out.
Comparing asexual and sexual reproduction
When conditions are right, the faster they reproduce, the better their chance of survival over other organisms using the same resources. Having offspring that are genetically identical is also an advantage as long as conditions remain favorable. However, a lack of genetic diversity becomes a disadvantage when conditions change in ways that do not fit the characteristics of an organism (asexual). Sexual reproduction is a different type of survival strategy. The process of finding a mate and the growth and development of offspring require more time. However, this can be an advantage for species that live in environments where seasonal changes affect weather conditions and food availability. Sexual reproduction also provides genetic diversity. If an environment changes, some offspring may have the right combination of characteristics needed to survive
-yeasts-reproduce asexually and sexually (asexually most of the time)
Genetic information that is bundled into packages of DNA
-Scale; a 300 meter rope stuffed into a school backpack
-E. coli bacterium's DNA molecule is 1.6mm, roughly 1000 times longer than the cell itself.
-Chromosomes make it possible to separate DNA precisely during cell division.
-Their DNA molecules are found in the cytoplasm along with most of the other contents of the cell. Most prokaryotes contain a single, circular DNA chromosome that contains all or nearly all of the cell's genetic information.
Eukaryotic cells generally have much more DNA than prokaryotes have and therefore, contain multiple chromosomes
-fruit flies-8 chromosomes
-human cells-46 chromosomes
-carrot cells-18 chromosomes
-The chromosomes in eukaryotic cells form a close association with histones, a type of protein. This complex of chromosome and protein is referred to as chromatin. DNA tightly coils around the histones, and together, the DNA and the histone molecules form
beadlike structures called nucleosomes. Nucleosomes pack together to form thick fibers, which condense even further during cell division. Usually the chromosome shape we see drawn is a duplicated chromosome with supercoiled chromatin.
Cells go through a series of events known as the cell cycle as they grow and divide.
-During the cell cycle, a cell grows, prepares for division, and divides to form two daughter cells. Each daughter cell then moves into a new cell cycle of activity, growth, and division.
Prokaryotic Cell cycle
-regular pattern of growth, DNA replication, and cell division that can take place very rapidly under ideal conditions.
-little is known about the details of the cell cycle in prokaryotes, and researchers are only just beginning to understand how it works.
-It is know that most prokaryotic cells begin to replicate their DNA chromosomes once they have grown to a certain size. When the replication is complete, the cell begins to divide.
-The process of cell division in prokaryotes is a form of asexual reproduction known as binary fission.
-Once the chromosome has been replicated, the two DNA molecules attach to different regions of the cell membrane. A network of fibers forms between them, stretching from one side of the cell to the other. The fibers constrict and the cell is pinched inward, dividing the cytoplasm and chromosomes between two newly formed cells. Binary fission results in the production of two genetically identical cells.
The eukaryotic cell cycle
Much more is known about the eukaryotic cell cycle.
-The eukaryotic cell cycle consists of four phases: G1, S, G2, and M (and G0 as resting period)
-Length of each part of cell cycle and the length of the entire cell cycle varies depending on the type of cell.
"in between" period of growth
-A great deal happens in the time between cell divisions
-Interphase is divided into three parts G1, S, and G2
G1 phase: Cell Growth
Cells do most of their growing during the G1 phase
-In this phase, cells increase in size and synthesize new proteins and organelles.
-The G in G1 and G2 stands for "gap", but these phases are actually periods of intense growth and activity.
S phase: DNA replication
The G1 phase is followed by the S phase.
-The S stands for "synthesis" and during this phase, new DNA is synthesized when the chromosomes are replicated. The cell at the end of the S phase contains twice as much DNA as it did at the beginning.
G2 phase: Preparing for cell division
When DNA replication is completed, the cell enters the G2 phase.
-G2 is usually the shortest of the three phases of interphase
-During this phase, many of the organelles and molecules required for cell division are produced
-When the events of the G2 phase are completed, the cell is ready to enter the M phase and begin the process of cell division.
M phase: Cell division
The M phase of the cell cycle, which follows interphase, produces two daughter cells.
-The M phase takes its name from the process of mitosis. During the normal cell cycle, interphase can be quite long. In contrast, the process of cell division usually takes place quickly.
Cell division in eukaryotes
Cell division in eukaryotes occurs in two main stages.
-The first stage of the process, division of the cell nucleus, is called mitosis.
-The second stage, the division of the cytoplasm, is called cytokinesis.
-In many cells, the two stages may overlap, so that cytokinesis begins while mitosis is still taking place.
The four phases of mitosis: prophase, metaphase, anaphase, and telophase
-Depending on the type of cell, mitosis may last anywhere from a few minutes to several days
The first phase of mitosis, and is usually the longest and may take up to half of the total time required to complete mitosis.
- During prophase, the genetic material inside the nucleus condenses and the duplicated chromosomes become visible. Outside the nucleus, a spindle starts to form.
-The duplicated strands of the DNA molecule can be seen to be attached along their length at an area called the centromere.
-Each DNA strand in the duplicated chromosome is referred to as a chromatid, or sister chromatid.
-When the process of mitosis is complete, the chromatids will have separated and been divided between the new daughter cells
-Also, during prophase, the cell starts to build a spindle, a fanlike system of microtubules that will help to separate the duplicated chromosomes. Spindle fibers extend from a region called the centrosome, where tiny paired structures called centrioles are located. Plant cells lack centrioles, and organize spindles directly from their centrosome regions.
-The centrioles, which were duplicated during interphase, start to move toward opposite ends, or poles, of the cell. As prophase ends, the chromosomes coil more tightly, the nucleolus disappears, and the nuclear envelope breaks down.
The second phase of mitosis, and is generally the shortest.
-During metaphase, the centromeres of the duplicated chromosomes line up across the center of the cell. Spindle fibers connect the centromere of each chromosome to the two poles of the spindle.
The third phase of mitosis and begins when sister chromatids suddenly separate and begin to move apart.
-Once anaphase begins, each sister chromatid is know considered an individual chromosome.
-During anaphase, the chromosomes separate and move along the spindle fibers to opposite ends of the cell.
-Anaphase comes to an end when this movement stops and the chromosomes are completely separated into two groups.
Following anaphase is telophase, the fourth and final phase of mitosis.
-During telophase, the chromosomes, which were distinct and condensed, begin to spread out into a tangle of chromatin.
-A nuclear envelope re-forms around each cluster of chromosomes.
-The spindle begins to break apart, and a nucleolus becomes visible in each daughter nucleus. Mitosis is complete, but the process of cell division has one more step to go.
As a result of mitosis, two nuclei-each with a duplicate set of chromosomes-are formed.
-All that remains to complete the M phase of the cycle is cytokinesis, the division of the cytoplasm itself.
-Cytokinesis usually occurs at the same time as telophase.
-Cytokinesis completes the process of cell division-it splits one cell into two.
-The process of cytokinesis differs in plant and animal cells.
Cytokinesis in Animal cells
During cytokinesis in most animal cells, the cell membrane is drawn inward until the cytoplasm is pinched into two nearly equal parts. Each part contains its own nucleus and cytoplasmic organelles
Cytokinesis in Plant cells
The cell membrane is not flexible enough to draw inward because of the rigid cell wall that surrounds it. Instead, a structure known as the cell plate forms halfway between the divided nuclei. The cell plate gradually develops into cell membranes that separate the two daughter cells. A cell wall then forms in between the two new membranes, completing the process.
Regulating the cell cycle
In the human body, most muscle cells and nerve cells do not divide at all once they have developed.
-In contrast, cells in the bone marrow that make blood cells and cells of the skin and digestive tract grow and divide rapidly throughout life. These cells may pass through a complete cycle every few hours. This process provides new cells to replace those that wear out or break down
Controls on Cell division
When an injury such as a cut in the skin or a break in a bone occurs, cells at the edges of the injury are stimulated to divide rapidly. New cells form, starting the process of healing. When the healing process nears completion, the rate of cell division slows, controls on growth are restored, and everything returns to normal.
The discovery of Cyclins
For many years, biologists searched for a signal that might regulate the cell cycle-something that would "tell" cells when it was time to divide, duplicate their chromosomes, or enter another phase of the cell cycle.
-In the early 1980s, biologists discovered a protein in cells that were in mitosis.
-Named the protein cyclin because it seemed to regulate the cell cycle.
- cyclin-dependent kinases (CDKs)
-Investigators have since discovered a family of proteins known as cyclins that regulate the timing of the cell cycle in eukaryotic cells.
Scientists have since identified dozens of other proteins that also help to regulate the cell cycle. The cell cycle is controlled by regulatory proteins both inside and outside the cell.
Respond to events occurring inside a cell. Internal regulatory proteins allow the cell cycle to proceed only when certain events have occurred in the cell itself.
-ex. several regulatory proteins make sure a cell does not enter mitosis until its chromosomes have replicated. Another regulatory protein prevents a cell from entering anaphase until the spindle fibers have attached to the chromosomes.
Proteins that respond to events outside the cell.
-external regulatory proteins direct cells to speed up or slow down the cell cycle.
-One important group of external regulatory proteins is the group made up of the growth factors. Growth factors stimulate the growth and division of cells.
-These proteins are especially important during embryonic development and wound healing.
-Other external regulatory proteins on the surface of neighboring cells often have an opposite effect. They cause cells to slow down or stop their cell cycles. This prevents excessive cell growth and keeps body tissues from disrupting one another.
Cells end their life cycle in one of two ways; they might actually die by accident due to damage or injury, or a cell may actually be "programmed" to die.
-Apoptosis is a process of programmed cell death.
-Once apoptosis is triggered, a cell undergoes a series of controlled steps leading to its self-destruction.
-First, the cell and its chromatin shrinks, and then parts of the cell's membrane breaks off. Neighboring cells then quickly clean up the cell's remains.
-Apoptosis also plays a key role in development by shaping the structure of tissues and organs in plants and animals.
-When apoptosis does not occur as it should, a number of diseases can result. For example, the cell loss seen in AIDS and Parkinson's disease can result if too much apoptosis occurs.
-Creates the shape of hands and feet in organisms and occurs when leaves fall off of trees.
Cancer: Uncontrolled cell growth
Cell growth is carefully regulated because the consequences of uncontrolled cell growth in a multicellular organism are very severe.
-Cancer is a disorder in which body cells lose the ability to control growth.
-Cancer cells do not respond to the signals that regulate the growth of most cells. As a result, the cells divide uncontrollably
-Cancer cells form a mass of cells called a tumor. Some are serious, while others are benign.
-benign-does not spread to surrounding healthy tissue or to other parts of the body.
-Cancerous tumors-malignant tumors that destroy and invade surrounding healthy tissue.
-As cancer cells spread, they absorb the nutrients needed by other cells, block nerve connections, and prevent the organs they invade from functioning properly.
What causes cancer?
Cancers are caused by defects that regulate cell growth and division.
-There are several sources of such defects, such as smoking or chewing tobacco, radiation exposure (UV, x-rays, radioactive chemicals), other defective genes, and even viral infection, and asbestos.
-All cancers have one thing in common: the control over the cell cycle has broken down. Some cancer cells will no longer respond to external growth regulators, while others fail to produce the internal regulators that ensure orderly growth.
-astonishing number of cancer cells have a defect in a gene called p53, which normally halts the cell cycle until all chromosomes have been properly replicated. Damaged or defective p53 genes cause cells to lose the information needed to respond to signals that
normally control their growth.
-carcinogens-substances that can cause mutations that lead to cancer (ex. tobacco/nicotine)
Treatments for cancer
Cancer cells grow rapidly, and therefore, need to copy their DNA more quickly than do most normal cells. This makes them especially vulnerable to damage from radiation. Many tumors can be effectively treated with carefully targeted beams of radiation.
-Chemotherapy-chemical compounds that kill cancer cells, or slow their growth. Chemotherapy has made it possible to cure some forms of cancer. However, since chemotherapy compounds target rapidly dividing cells, they also interfere with cell division in normal, healthy cells. This produces serious side effects in many patients, and it is one of the reasons why scientists are so interested in gaining a better understanding of the role of cell cycle proteins in cancer. Cancer is a disease of the cell cycle, and conquering cancer will require a much deeper understanding of the processes that control cell division.
process by which a cell becomes a specific type of cell in an organism.
Cells that are undifferentiated or not specialized.
Embryonic stem cells
completely undifferentiated and can become any type of cell.
Adult stem cells
come from developed organisms
Two hit hypothesis
Cells need one mutation of each type to become cancerous.
-mutations that affect the cell cycle
-mutations that affect a cell's DNA repair mechanisms
cancerous cells spread through the blood stream.
advancing from one stage to the next requires a signal (regulatory proteins)
Ways materials move around inside cells
reasons a cell needs to divide
made of microtubules; role in cell division
Normal cell cycle controls
abnormal cell cycle
loss of control leads to cancerous cells.
Causes of cancer
-environmental (carcinogens): chemical and radiation
Stem cells (two types, importance in research and medicine, ethical dilemmas)
-Embryonic stem cells and Adult stem cells are the two kinds of stem cells.
-Stem cells offer the potential benefit of using undifferentiated cells to repair or replace badly damaged cells and tissues.
-(after heart attacks, strokes, and spinal cord injuries) because heart attacks destroy cells in the heart muscle, strokes injure brain cells, and spinal cord injuries cause paralysis by breaking connections between nerve cells.
-To obtain embryonic stem cells, you have to get them from very early embryos and in order to get these stem cells, the embryo is usually destroyed. Many ethical issues and ethical questions raised about killing another life to obtain these embryonic stem cells.
-Not the same problem for adult stem cells, since they can be obtained directly from the body of a willing donor, so research with these cells has raised few ethical questions to date.
- research for embryonic stem cells is also questioned because their are many arguments as to whether it is ethical or not. This concern has made government fundings of embryonic stem cell research an important political issue.