Test #3 Study Flashcards
How do cells divide in mitosis?
the division of a cell’s nucleus.
Along with cytokinesis (the division of the rest of a cell),
results in a parent cell dividing into two daughter cells
The genetic information within each of these daughter cells is identical.
How do cells divide in Meiosis?
a type of cell division specific to reproduction,
halving the number of chromosomes in a cell.
humans’ cells contain
46 chromosomes
What happens if the cell did not have half of the 46 chromosomes in the sperm and egg?
a fertilized egg will contain 92 chromosomes and be unable to maintain its proper functions
Interphase for Mitosis and Interphase I for Meiosis (first)
is the period between cell divisions
chromosomes replicate—each DNA strand unzips into two strands while free-floating bases attach to the unzipped strands
chromosomes are loosely packed
Two pair of centrioles lie just outside the nucleus, next to each other.
A centriole is a cylindrical structure within the cell helps with reproduction.
Prophase for Mitosis (second)
chromosomes begin to condense
four arms connected at a point. Each chromosome is, at this time, actually two identical copies. Each copy is called a chromatid.
A spindle begins to form from the centrioles. This spindle is made of fibers. The centrioles begin to separate.
Prophase I for Meiosis
same as prophase for Mitosis only difference:
except that in this cell the chromosomes attach to the membrane of the nucleus and then pair up with their corresponding chromosome.
While paired up, enzymes cut sequences of DNA (genes) from the chromosomes. These sequences are exchanged between the chromosomes, which allows for an exchange of genes between the two.
Prometaphase in Mitosis
The centrioles are now at opposite ends of the cell.
The spindle fibers from both of the centrioles attach to each one of the chromosomes.
Prometaphase I in Meiosis
Same as in mitosis, except that the spindle fibers from each centriole attach to one chromosome of a matching chromosome pair.
In other words, the fibers from one centriole attach to 23 chromosomes, and the fibers from the other centriole attach to the other 23 chromosomes.
Metaphase in Mitosis (third)
The chromosomes line up on the metaphase plate, an imaginary line that divides the cell in two.
Also, the fibers begin to tug each chromosome toward opposite ends of the cell.
Metaphase in Meiosis
Same as in mitosis, except that the chromosome pairs line up on either side of the metaphase plate.
Anaphase in Mitosis (fourth)
The fibers pull the chromatids toward opposite ends of the cell.
Anaphase I in Meiosis
The chromosome pairs separate; half of the chromosomes move toward one end of the cell, the other half, to the other end.
The chromosomes’ sister chromatids do not separate as they do in mitosis
Telophase in Mitosis (fifth)
The chromatids (now also considered chromosomes) arrive at the opposite ends of the cell, and new nuclear membranes form.
Mitosis, which describes only the division of the nucleus, is now complete.
Telophase I in Meiosis
As in mitosis, the chromosomes arrive at opposite ends of the cell, and new nuclear membranes form.
End of cytokinesis in mitosis and meiosis
The rest of the cell divides.
Cytokinesis, the division of the cell’s cytoplasm, is now complete.
Interphase II Meiosis
Mitosis is finished by this point
The chromosomes do not replicate during this phase, as they do in interphase in mitosis and interphase I in meiosis.
Prophase II in meiosis
As in prophase I, the chromosomes condense, spindles form, the centrioles begin to separate, and the nuclear membrane fragments and disperses.
Unlike prophase I, the chromosomes do not attach to the nuclear membrane in order to exchange genetic information.
Prometaphase II in meiosis
The spindle fibers attach to the chromosomes. The centrioles are now at opposite ends of the cell.
As in mitosis prometaphase, fibers from both ends of the cells attach to each one of the four chromosomes.
Metaphase II in meiosis
The chromosomes align along the metaphase plate.
As in mitosis metaphase, (and unlike meiosis metaphase I), fibers from the centrioles begin to pull on each one of the chromosomes from both directions
Anaphase II in meiosis
As in anaphase in mitosis (and unlike anaphase I in meiosis), the fibers pull the chromatids apart and toward opposite ends of the cells.
Telophase II in meiosis
The chromatids arrive at the either end of each cell and new nuclear membranes form.
With meiosis in a female, there is only one dividing cell at this point. As in telophase I, the cytoplasm of the cell will be concentrated in one of the two emerging cells. The resulting large cell will become an egg cell. The smaller cell will degenerate
End of cytokinesis in meiosis
The rest of the cell continues to divide. Only when two, distinct cells form will cytokinesis, the division of the cell’s cytoplasm, be complete.
There are now four daughter cells. Each cell has one set of chromosomes, or one half the number of the initial cell.
Why do cell divide?
to make new cells
A single cell divides to make two cells and these two cells then divide to make four cells, and so on.
We call this process “cell division” and “cell reproduction,” because new cells are formed when old cells divide
What is interphase?
is the longest stage in the eukaryote cell cycle
prepares cells for cell division
the cell acquires nutrients, creates and uses proteins and other molecules, and starts the process of cell division by replicating the DNA
Stage of Interphase
Gap 1 or G1
After cells have finished dividing their chromosomes, and cytokinesis has divided the cell membrane, the two new cells enter the first stage of interphase, Gap 1 or G1.
During this stage, the cell performs its normal functions, and grows in size.
Stage of Interphase
Synthesis
the cell pauses its normal functioning
All resources are dedicated to replicating the DNA. This process starts with the two entwined stands of DNA being “unzipped” by various proteins. Other proteins, known as polymerase enzymes, start creating new strands to pair with each half of the DNA
Stage of Interphase
Gap 2 or G2
During G2 the cell the cell adds volume to the cytoplasm, and replicates many important organelles
In animals, the mitochondria are replicated to provide enough energy for the dividing cell.
In plants, both the mitochondria and the chloroplasts must be replicated to provide the daughter cells with organelles capable of producing energy
What is Mitosis?
A type of cell division in eukaryotes that creates identical daughter cells.
Mitosis is a process of nuclear division in eukaryotic cells that occurs when a parent cell divides to produce two identical daughter cells
What is Cytokinesis?
The division of a cell membrane into two cells; the process that completes cell division.
What is Meiosis?
Two consecutive cell divisions between which no DNA replication takes place.
A cell just finished dividing. It starts gathering nutrients and growing. It stops growing, and does not start DNA replication. What stage is the cell in?
G0
This cell remains in resting phase
it will not continue dividing until it receives signals from the body to do so.
These signals could come from damage to nearby cell or from growth hormones telling the body to expand. Until then, the cell will remain in G0.
A cell has grown a little, and replicated its DNA. What comes next?
Gap2
The cell has just replicated its DNA, which is the interphase stage of synthesis.
The next stage is Gap 2, where the cell must prepare for cell division.
Without the increased size and organelles produced in Gap 2, the cell would not have enough material to divide and would be much too small after division.
Why is there no interphase in bacteria?
Bacteria have no distinct organelles
The bacterial cell cycle is divided into 4 phases, A, B, C, and D, which roughly correspond to the various stages of the eukaryotic cell cycle. While A is the process of binary fission in bacteria, B, C, and D are similar to interphase in that the cell functions normally and duplicates its DNA.
what type of cells undergo mitosis?
Somatic cells: are the regular cells in the body of multicellular organisms. Some examples of somatic cells are epithelial cells, muscle cells, liver cells, etc
Adult stem cells:
Some very specialized somatic cells such as cardiac muscle cells, nerve cells, and red blood cells do not undergo mitosis. These types of cells are differentiated from adult stem cells, not from cell division
Cells in the embryo:
Zygote is the conceptus of fertilization, and it is composed of a single cell with a diploid nucleus. It undergoes three mitotic divisions to form eight-cell stage called the blastocyst. Blastocyst undergoes a large number of mitotic divisions while developing into a young.
Organelles in mitosis to make the world spin
the nucleus, mitotic spindle and microtubules.
What are microtubules and what is their role in cell division?
hollow tubes
roles in cell movement, cell division, and transporting materials within cells.
a network of protein filaments that extends throughout the cell, gives the cell shape, and keeps its organelles in place. Microtubules are the largest structures in the cytoskeleton
What is the difference between a chromosome, gene, and genome?
genes are building blocks for your body. some give the instructions to make proteins. A protein’s job is to tell your body what types of physical characteristics you should have, like your hair and eye color. Some genes code for RNA, which does other jobs.
Chromosomes are structures that look like thread, which live in the nucleus (center) of cells. Chromosomes contain DNA and protein, and they come in different sizes. Proteins called histones allow them to pack up small enough to fit in a nucleus. histones make chromosomes smaller to fit in our body
genomes are all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding genes, other functional regions of the genome such as regulatory sequences
Which cells undergo mitosis and which cells undergo meiosis?
mitosis is with somatic cells and ends with two identical cells
meiosis is with germ cells that divide for sperm and egg producing cells that only have one copy of each type of chromosomes (haploid)
When is DNA in chromatin form?
mainly in interphase
when cells prepare to divide, chromatin condenses into chromosomes to get accurate genetic material
When is DNA in chromosome form?
during cell division, during mitosis and meiosis
in mitosis,
Prophase: Chromatin condenses into visible chromosomes, each consisting of two sister chromatids joined at a centromere.
Metaphase: Chromosomes align at the cell’s equatorial plane (metaphase plate).
Anaphase: Sister chromatids are pulled apart to opposite poles of the cell.
Telophase: Chromatids reach the poles, and the cell begins to divide. Chromosomes start to de-condense back into chromatin.
in meiosis,
Meiosis I: Homologous chromosomes pair up and undergo crossing over during prophase I, then align at the metaphase plate, separate during anaphase I, and reach the poles by telophase I.
Meiosis II: Similar to mitosis, where sister chromatids align, separate, and reach opposite poles, ending with the formation of four haploid cells.
what are centromeres and kinetochores
centromere is a region on a chromosome where sister chromatids are joined together
plays crucial role during cell division by ensuring correct segregation of chromatids into daughter cells
position can vary, it can be at the center or towards one end or at the very end.
Kinetochores are protein complexes that assemble on end of centromere during cell division
Serve as attachment for spindle fibers (microtubules) that pull chromatids apart to opposite poles of cell.
consist of inner region directly attached to centromere DNA and outer region that interacts with spindle fibers
What are centrosomes?
organelles that play role in organizing microtubules and getting cell division started
composed two centrioles surrounded by mass of proteins called pericentriolar material
serve as main microtubule organizing centers in animal cells
What is centrosome’s role in cell division
Microtubule Organization: Centrosomes organize the microtubules, which are essential for forming the mitotic spindle.
spindle formation: during prophase, centrosomes duplicate, then move opposite ends= bipolar spindle apparatus
chromosome segregation: spindle fibers (microtubules) attach to kinetochores to ensure segregation of daughter cells during anaphase
How is the cell cycle regulated?
by signals and checkpoints
G1 Checkpoint (Restriction Point): Assesses cell size, nutrient availability, and DNA integrity. If conditions are favorable, the cell commits to DNA replication.
G2 Checkpoint: Ensures DNA replication is complete and checks for DNA damage. If issues are detected, the cell cycle is halted for repairs.
M Checkpoint (Spindle Checkpoint): Occurs during metaphase of mitosis. Ensures all chromosomes are properly attached to the mitotic spindle before proceeding to anaphase.
What is the role of positive regulators in the cell cycle? What is the role of negative regulators in the cell cycle?
positive regulators:
These proteins promote cell cycle progression.
Examples: Cyclins and CDKs.
negative regulators:
hese proteins inhibit cell cycle progression to prevent uncontrolled cell division.
Examples: Tumor suppressor proteins like p53 and Rb.
what are cyclins and what do they do
Proteins that regulate the cell cycle by binding to and activating CDKs.
Cyclins bind to CDKs, resulting in the activation of the kinase activity of CDKs.
What are cyclin-dependent kinases and what do they do?
CDKs are a family of protein kinases that, when activated by binding to cyclins, phosphorylate target proteins to drive cell cycle progression.
Function: CDKs add phosphate groups to specific substrates, which can activate or deactivate these proteins, leading to changes in cellular processes that promote the progression through different stages of the cell cycle.
relationship between cyclins and CDKs
Cyclins and CDKs form complexes that are essential for the regulation of the cell cycle.
Cyclins act as regulatory subunits, while CDKs serve as catalytic subunits. The binding of a cyclin to a CDK activates the kinase activity of the CDK, allowing it to phosphorylate target proteins.
Describe how they promote the cell cycle.
G1 Phase: Cyclin D binds to CDK4 and CDK6, forming active complexes that phosphorylate the retinoblastoma (Rb) protein.
S Phase: Cyclin E binds to CDK2, forming a complex that further phosphorylates Rb and other targets, driving the cell into the S phase, where DNA replication occurs.
G2 Phase: Cyclin A binds to CDK2, forming a complex that is essential for the completion of DNA replication and preparation for mitosis.
M Phase: Cyclin B binds to CDK1, forming the maturation-promoting factor (MPF) complex that triggers the entry into mitosis by phosphorylating various substrates involved in chromosome condensation, spindle formation, and other mitotic events.
what are proto-oncogenes and oncogenes?
Proto-oncogenes are normal genes that regulate cell growth, division, and differentiation. They encode proteins that stimulate cell proliferation and survival.
Function: These genes are essential for normal cellular functions, such as growth factors, growth factor receptors, signal transduction proteins, and transcription factors.
Oncogenes are mutated or abnormally activated versions of proto-oncogenes. They can cause uncontrolled cell growth and division, leading to cancer.
Function: Oncogenes result from mutations, amplifications, or overexpression of proto-oncogenes, leading to the production of proteins that drive continuous cell proliferation without normal regulatory controls.
What are tumor suppressor proteins?
Tumor suppressor proteins are proteins encoded by tumor suppressor genes that inhibit cell proliferation, promote DNA repair, and induce apoptosis (programmed cell death) when necessary.
Function: These proteins act as brakes on cell division, ensuring that cells only divide when conditions are favorable and that damaged cells do not continue to proliferate.
Describe how mutations in proto-oncogenes and tumor suppressor proteins lead to cancer.
mutations in proto-oncogenes and tumor suppressor proteins disrupt the delicate balance of cell regulation, leading to uncontrolled cell growth and the development of cancer. Understanding these mechanisms is crucial for developing targeted therapies and improving cancer treatment.
Point Mutations: A single nucleotide change can result in a hyperactive protein product.
Gene Amplification: An increase in the number of copies of a proto-oncogene can lead to overproduction of the protein, driving uncontrolled cell growth.
Chromosomal Translocations: Rearrangement of chromosomal segments can create fusion proteins with oncogenic properties
Insertions/Deletions: These can lead to frameshift mutations or altered protein products with oncogenic activity.
What is the purpose of meiosis?
Meiosis is a special type of cell division that reduces the chromosome number by half, resulting in the production of haploid cells (gametes) from diploid cells. The main purpose of meiosis is to ensure genetic diversity and maintain the correct chromosome number in sexually reproducing organisms.
production of gametes:
meiosis produces sperm and egg cells with half the number of chromosomes as the parent cell, ensuring fertilization occurs
Genetic diversity
Which body cells undergo meiosis
Germ Cells: Meiosis occurs in specialized cells called germ cells, which are found in the reproductive organs.
In males, germ cells in the testes undergo meiosis to produce sperm cells.
In females, germ cells in the ovaries undergo meiosis to produce egg cells (oocytes).
The end result of meiosis is four genetically diverse haploid cells, each with half the chromosome number of the original diploid cell. This diversity and reduction in chromosome number are key to the success of sexual reproduction.
How is meiosis different from mitosis?
Number of divisions:
Mitosis: Involves one division cycle, resulting in two daughter cells.
Meiosis: Involves two division cycles (meiosis I and meiosis II), resulting in four daughter cells.
purpose:
Mitosis: Produces two genetically identical diploid daughter cells from a single diploid parent cell. It’s involved in growth, tissue repair, and asexual reproduction.
Meiosis: Produces four genetically diverse haploid cells (gametes) from a single diploid parent cell. It’s involved in sexual reproduction, generating genetic diversity.
chromosomes number:
Mitosis: Maintains the diploid chromosome number (2n) in daughter cells, identical to the parent cell.
Meiosis: Reduces the chromosome number by half, producing haploid (n) gametes.
stages:
Mitosis:
Prophase: Chromosomes condense, and the nuclear envelope breaks down.
Metaphase: Chromosomes align at the metaphase plate.
Anaphase: Sister chromatids are pulled apart to opposite poles.
Telophase: Chromatids reach the poles, and the nuclear envelope reforms.
Cytokinesis: Cytoplasm divides, resulting in two daughter cells.
Meiosis:
Meiosis I:
Prophase I: Homologous chromosomes pair up and undergo crossing over.
Metaphase I: Homologous chromosome pairs align at the metaphase plate.
Anaphase I: Homologous chromosomes (each with two sister chromatids) are pulled apart.
Telophase I and Cytokinesis: Two haploid cells form, each with half
the number of chromosomes.
Meiosis II: (Similar to mitosis)
Prophase II: Chromosomes condense in the two new cells.
Metaphase II: Chromosomes align at the metaphase plate.
Anaphase II: Sister chromatids are pulled apart to opposite poles.
Telophase II and Cytokinesis: Four genetically diverse haploid cells form.
genetic variation:
Mitosis: Produces genetically identical daughter cells.
Meiosis: Introduces genetic variation through crossing over (exchange of genetic material between homologous chromosomes during prophase I) and independent assortment (random orientation of homologous chromosome pairs during metaphase I).
What is reduction division?
is another term for the first division in meiosis, also known as meiosis I. It is called reduction division because it reduces the chromosome number by half, resulting in haploid cells from a diploid parent cell. Here’s a more detailed look at the process:
what is crossing over
process during which homologous chromosomes exchange genetic material.
Crossing over is the exchange of genetic material between non-sister chromatids of homologous chromosome
This process creates new combinations of alleles on each chromosome, increasing genetic variation among offspring.es during meiosis.
when does crossing over occur
Prophase I of Meiosis: Crossing over occurs during prophase I of meiosis, when homologous chromosomes pair up to form tetrads. The chromosomes are aligned such that non-sister chromatids are close together.
Chiasmata Formation: The points where crossing over occurs are called chiasmata. These are visible under a microscope as cross-shaped structures between homologous chromosomes.
steps of crossing over
Synapsis: Homologous chromosomes pair up and align closely with each other.
Formation of Chiasmata: Non-sister chromatids break at corresponding points and exchange segments of genetic material.
Recombination: The exchanged segments are rejoined, leading to a recombination of genetic material on the chromatids.
When does independent assortment happen?
occurs during metaphase I of meiosis
It refers to the random orientation of homologous chromosome pairs (tetrads) on the metaphase plate. This process contributes to genetic diversity by allowing different combinations of maternal and paternal chromosomes to be distributed to the gametes.
Describe multiple ways that genetic variation is generated during meiosis, including crossing-over and independent assortment.
These mechanisms ensure that each gamete produced during meiosis is genetically unique, contributing to the genetic variation necessary for natural selection and adaptation in sexually reproducing organisms.
What is diploid?
refers to a cell or an organism that has two complete sets of chromosomes, one set inherited from each parent. Diploid cells are denoted as 2n.
most somatic cells, muscle cells, brain cells and skin cells
46 in humans
what is haploid
refers to a cell or an organism that has only one complete set of chromosomes. Haploid cells are denoted as n.
humans haploid is 23
Be able to identify the number of chromosomes in a given cell.
Diploid (2n) Cells: Contain two complete sets of chromosomes (e.g., 46 in humans).
Haploid (n) Cells: Contain one complete set of chromosomes (e.g., 23 in humans).
Somatic Cells (Body Cells):
Human Diploid Cells: 46 chromosomes (23 pairs)
Example: Skin cells, muscle cells, brain cells
- Gametes (Sex Cells):
Human Haploid Cells: 23 chromosomes (no pairs)
Example: Sperm cells, egg cells
- Zygotes:
Human Diploid Zygote: 46 chromosomes (23 pairs, formed from the fusion of two haploid gametes)
- Abnormal Chromosome Numbers:
Trisomy 21 (Down Syndrome): 47 chromosomes (extra chromosome 21)
Turner Syndrome: 45 chromosomes (missing one X chromosome)
