Omics-C10 Flashcards
Cell Division
Prokaryotic organisms like bacteria have a single, circular DNA molecule located in a region called the ____. Some also contain smaller loops of DNA called ____, which can carry advantageous traits such as antibiotic resistance.
eukaryotes (including humans) have multiple, linear chromosomes housed within the nucleus. These chromosomes are composed of ____, a complex of DNA and protein.
nucleoid
plasmids
chromatin
Histone proteins wrapped by DNA form Nucleosome, Coiled Nucleosomes form Chromatin, Condensed chromatins form Chromosomes
Note: Chromatin is a decondensed or unpacked chromosome found in a cell when not in cell division. Chromatid is one of the two identical halves of a chromosome replicated during cell division.
Cell Division
Chromosomes in eukaryotic cells are further compacted using ____ proteins, forming a structure known as a nucleosome.
histone
Cell Division
Human body cells are ____, meaning they contain two sets of chromosomes (46 total), one set inherited from each parent. Reproductive cells (gametes) are ____, containing only one set of chromosomes (23 total).
diploid
haploid
Cell Division
What are genes?
Genes are segments of DNA located on chromosomes that determine specific traits.
a sequence of nucleotides in DNA that is transcribed to produce a functional RNA
All the DNA contained in one cell is called the genome
Cell Division
What are somatic cells?
Somatic cells are the cells in the body other than sperm and egg cells (which are called germ cells).
Cell Division
Upon fertilization, each gamete contributes one set of chromosomes, creating a diploid cell containing
matched pairs of chromosomes called ____ chromosomes.
homologous (“same knowledge”)
Homologous chromosomes are the same length and have specific nucleotide segments called genes in exactly the same location, or locus.
Cell Cycle
what is the Interphase stage of cell cycle? and what are its thress sub-phases?
Link
Interphase: This is the preparatory phase, where the cell grows and replicates its DNA. It is divided into three sub-phases:
G1 Phase (First Gap): The cell grows, carries out what it’s supposed to do and prepares the necessary components for DNA replication.
S Phase (Synthesis): DNA is replicated, creating identical sister chromatids.
G2 Phase (Second Gap): Further growth occurs, and the cell ensures everything is ready for mitosis.
Cell Cycle
What happens after the interphase, during the mitotic phase of cell division? what are the two stages it includes?
Mitotic Phase: The cell divides its replicated DNA and cytoplasm to produce two identical daughter cells. It includes two stages:
Mitosis (Karyokinesis): The nucleus divides through five steps—prophase, prometaphase, metaphase, anaphase, and telophase.
Cytokinesis: The cytoplasmic contents are divided, resulting in two separate daughter cells. In animal cells, this is done by an actin ring, while plant cells use cell plate formation.
Cell Cycle
What is G0 Phase?
Not all cells go through the typical cell cycle. Some enter the G0 phase, where they stop dividing and exit the cycle temporarily or permanently, as in the case of nerve and heart muscle cells.
Cell Cycle
Prophase:
* Chromosomes condense and become visible.
* Spindle fibers emerge from the centrosomes.
* Nuclear envelope breaks down.
* Nucleolus disappears.
Prometaphase:
* Chromosomes continue to condense.
* Kinetochores appear at the centromeres.
* Mitotic spindle microtubules attach to kinetochores.
* Centrosomes0 move toward opposite poles.
Metaphase:
* Mitotic spindle1 if fully developed, centrosomes are at the opposite poles of the cell.
* Chromosomes are lined up at the metaphase plate2.
* Each sister chromatidis3 attached to a spindle fiber originating from opposite poles.
Anaphase:
* Cohesin proteins binding the sister chromatids together break down.
* Sister chromatids (now called chromosomes) are pulled toward the opposite poles.
* Non-kinetochore spindle fibers lengthen, elongating the cell.
Telophase:
* Chromosomes arrive at opposite poles and begin to decondense.
* Nuclear envelope material surrounds each set of chromosomes.
* The mitotic spindle breaks down.
0 Centrosomes are membrane-free organelles that serve as main microtubule-organizing centres in distinct eukaryotic lineages.
1 The mitotic spindle is a structure that forms during cell division and separates duplicated chromosomes
2 The metaphase plate is an imaginary plane axis that divides the cell into two.
3 A chromatid is one of the two identical halves of a chromosome that has been replicated in preparation for cell division.
Cell Cycle
How is cytokinesis different in animal and plant cells?
Cleavage Furrow Formation: In animal cells, cytokinesis is accomplished by forming a cleavage furrow. This is an indentation of the plasma membrane that occurs midway between the two daughter nuclei.
Contractile Ring: The furrow is created by a contractile ring made up of actin filaments. As this ring tightens, it pinches the cell membrane inward until the cell is split into two separate daughter cells.
Flexible Plasma Membrane: The process is easier in animal cells because they lack a rigid cell wall, allowing the membrane to pinch inwards smoothly.
Cell Plate Formation: In plant cells, a cell plate forms at the center of the dividing cell, which eventually develops into a new cell wall. This process is necessary due to the rigidity of the cell wall.
Vesicle-Mediated Process: Vesicles derived from the Golgi apparatus move to the center of the cell, coalescing to form the cell plate. These vesicles carry materials like cellulose that will be used to form the new cell wall.
Formation of a New Cell Wall: As the vesicles fuse, they form the beginning of a new cell wall, dividing the cytoplasm into two daughter cells.
Summary:
Animal Cells: Form a cleavage furrow and use a contractile ring to pinch the cell into two.
Plant Cells: Form a cell plate that grows outward to form a new dividing wall between the two daughter cells.
Cell Cycle
The cell cycle has several checkpoints that ensure each phase is completed correctly before the cell moves on to the next phase. These checkpoints act as quality control systems. What are the major checkpoints?
Major Checkpoints:
G1 Checkpoint (Restriction Point):
This is the most crucial checkpoint, determining whether the cell will proceed with division.
The cell checks for adequate size, nutrients, DNA integrity, and external signals (like growth factors).
If conditions are not met, the cell enters the G0 phase, where it either pauses temporarily or stops dividing altogether.
G2 Checkpoint:
This checkpoint occurs at the end of the G2 phase, right before mitosis.
The cell checks for proper DNA replication, ensuring that the DNA is free of damage or mutations.
If the DNA is damaged or incomplete, the cell cycle halts to allow repair mechanisms to fix any issues.
M Checkpoint (Spindle Checkpoint):
This checkpoint occurs during mitosis, specifically at the metaphase stage.
The cell ensures that all the chromosomes are properly attached to the mitotic spindle and aligned at the metaphase plate.
If there is an error in spindle attachment, the cell pauses to correct it before completing division.
Control of the Cell Cycle
Two key types of molecules control the cell cycle: ____ and ____.
cyclins
cyclin-dependent kinases (CDKs)
The interaction between cyclins and CDKs acts as a switch for cell cycle progression. Specific cyclin-CDK complexes trigger different stages of the cycle:
G1 Cyclins and CDKs help the cell transition from G1 to the S phase.
G2 Cyclins and CDKs drive the cell from G2 to mitosis.
Control of the Cell Cycle
What are cyclin and CDKs?
Cyclins: Proteins that are synthesized and degraded in a cyclic manner during different stages of the cell cycle. Their levels fluctuate depending on the phase of the cell cycle.
CDKs (Cyclin-Dependent Kinases): Enzymes that bind to cyclins to become active. When activated, CDKs phosphorylate target proteins, driving the cell to the next phase of the cycle.
Two groups of proteins, called cyclins and cyclin-dependent kinases (Cdks), are termed positive regulators. They are responsible for the progress of the cell through the various checkpoints.
Control of the Cell Cycle
What do P53,P21 and RB proteins do?
p53 (a tetramer consisting of four monomers) detects DNA damage and halts the cell cycle by activating p21. p21 inhibits the cyclin-CDK complexes that are needed to phosphorylate RB, thus preventing the cell from entering the S phase.
RB Regulation: By keeping RB in its active, unphosphorylated state, p53 and p21 ensure that cells with damaged DNA do not progress to DNA replication. This coordinated action ensures that only healthy cells move through the cell cycle, preventing the development of cancer.
Cancer and Cell Cycle Deregulation:
When the regulatory mechanisms of the cell cycle fail, cells can begin dividing uncontrollably, which can lead to cancer.
Proto-oncogenes: Genes that promote cell division. When mutated, they become oncogenes, leading to uncontrolled division.
Tumor suppressor genes: Genes like p53 that normally stop cell division when there are problems. When these genes are mutated, cells can bypass checkpoints, allowing damaged or incomplete DNA to propagate, leading to cancer.
Rb, p53, and p21 act primarily at the G1 checkpoint.
Cyclins regulate the cell cycle only when they are tightly bound to Cdks. To be fully active, the Cdk/cyclin complex must also be phosphorylated1 in specific locations to activate the complex. Like all kinases, Cdks are enzymes (kinases) that in turn phosphorylate other proteins. Phosphorylation activates the protein by changing its shape. The proteins phosphorylated by Cdks are involved in advancing the cell to the next phase.
1 Phosphorylation is the process of adding a phosphate group (PO3-) to an organic molecule
Control of the Cell Cycle
Rb, which largely monitors cell size, exerts its regulatory influence on other positive regulator proteins. In the active, dephosphorylated state, Rb binds to proteins called transcription factors, most commonly, ____ (Figure 10.13).
Transcription factors “turn on” specific genes, allowing the production of proteins encoded by that gene. When Rb is bound to it, production of proteins necessary for the G1/S transition is blocked. As the cell increases in size, Rb is slowly phosphorylated until it becomes inactivated. Rb releases the transcription factor, which can now turn on the gene that produces the transition protein, and this particular block is removed.
E2F
Control of the Cell Cycle
Relation between MDM2 and P53?
When the cell is healthy, MDM2 keeps p53 in check by breaking it down, preventing p53 from stopping cell division.
When the cell is damaged (like from UV radiation or chemicals), p53 is activated to stop the cell from dividing, giving the cell time to repair or, if the damage is too bad, causing the cell to self-destruct.
Once the damage is repaired, MDM2 comes back to reduce p53 levels again, allowing the cell to continue growing.
In short, MDM2 acts like a controller for p53, making sure it’s only active when needed. If this balance is off, it can lead to uncontrolled cell growth, which can cause cancer.
Control of the Cell Cycle
Why is P53 so suseptible to mutation?
- p53 is essential for protecting the cell from DNA damage, so it’s often involved in high-risk situations where DNA is unstable or exposed to mutagens.
- Its complex structure, especially in the DNA-binding domain, makes it sensitive to mutations that can disrupt its function.
- Cancer cells often target p53 for mutation because disabling it allows for unchecked cell growth, leading to tumor development.
- The dominant-negative effect means that even a single mutant copy of p53 can greatly reduce its function. (p53 is a tetramer, meaning it functions as a group of four p53 proteins that bind together. A mutation in just one of the four p53 proteins can disrupt the entire complex, reducing its overall functionality. This dominant-negative effect means that even partial damage to p53 can have a large impact on its tumor-suppressing ability.)
External
What’s the difference between genes and allels?
An allele is a variant form of a gene. While a gene determines a particular trait, an allele is a specific version of that gene. For example, for the gene that controls eye color, there might be different alleles that result in blue eyes, brown eyes, or green eyes.
Organisms typically inherit two alleles for each gene, one from each parent. These alleles can be the same (homozygous) or different (heterozygous).
Cancer and the Cell Cycle
What are the key genes involved in cancer?
Proto-oncogenes: These are genes that normally help cells grow. When mutated, they become oncogenes, which push the cell to divide uncontrollably. In this case, they act like a “stuck gas pedal” in a car, making the cell cycle speed up without stopping.
Tumor Suppressor Genes: These genes normally act as brakes in the cell cycle, preventing uncontrolled growth. When they are mutated or inactivated (for example, p53), the “brakes” fail, and cells can keep dividing uncontrollably.
The combination of these mutations in oncogenes (accelerators) and tumor suppressor genes (brakes) leads to the development of cancer.
Which of the following events occurs during interphase of the cell cycle?
A) condensation of the chromosomes
B) separation of the spindle poles
C) spindle formation
D) replication of the DNA
D) replication of the DNA
Explanation:
Interphase is the phase of the cell cycle during which the cell prepares for division. It is divided into three sub-phases: G1 (cell growth), S (DNA replication), and G2 (further growth and preparation for mitosis).
During the S phase of interphase, the cell replicates its DNA, ensuring that each daughter cell will have an identical set of chromosomes after division.
The other options describe events that occur during mitosis (the M phase), not interphase:
A) Condensation of the chromosomes: This occurs during prophase of mitosis, when chromosomes become visible.
B) Separation of the spindle poles: This occurs during anaphase of mitosis when the spindle fibers pull sister chromatids apart.
C) Spindle formation: This happens in prophase of mitosis when the spindle apparatus forms to separate the chromosomes.
Thus, DNA replication is the key event of interphase.
