Cell Comm.
What is a major component of cell signaling cascades?
Phosphorylation!
Enzymes, known as kinases, will phosphorylate other molecules, such as other proteins, to transfer the signal throughout the cell.
What is cancer the result of?
Cancer is the result of unchecked cell division caused by a breakdown of the mechanisms that regulate the cell cycle.
Meiosis and fertilization alternate in sexual life cycles. How so?
The process of meiosis produces unique reproductive cells called gametes, which have half the number of chromosomes as the parent cell. Then, when two haploid gametes fuse, this restores the diploid condition in the new zygote.
What is true-breeding?
Plants that when self-crossed always produce the same plant variant.
How many chromosomes does a human gamete have?
Human gametes have 23 chromosomes, or one complete set of chromosomes.
This is the n or haploid state.
What allows for signal transduction through a cell?
Reception: A ligand (chemical signaling molecule) binds to the receptor protein.
This triggers a chain of events within the cell, known as a signaling pathway/ cascade, that leads to a cellular response.
Any disruption of the monitoring system can allow other mistakes to be passed on to the daughter cells. How so?
Each successive cell division will give rise to daughter cells with even more accumulated damage.
Eventually, all checkpoints become nonfunctional, and rapidly reproducing cells crowd out normal cells, resulting in a tumor or some sort of cancer.
How is genetic variation in populations produced?
1. Mutations (ex: lactose-tolerance).
2. Independent assortment (homologous chromosomes sort randomly during meiosis I).
3. Crossing over (The exchange of information between nonsister chromatids).
4. Random fertilization (when a sperm and an egg combine, the sperm and egg that come together are completely random).
What is the difference between the law of segregation and the law of independent assortment?
The law of segregation states that the two alleles of a gene separate so each gamete gets one allele, while the law of independent assortment states that alleles of different genes segregate independently during gamete formation.
Further: law of segregation states that each organism carries two alleles for a trait and these alleles separate during meiosis so each gamete receives one allele. The law of independent assortment states that alleles of different genes assort independently during gamete formation and the inheritance of one trait does not influence another.
How do females account for the X chromosome dosage?
X chromosome inactivation, described by the Lyon Hypothesis: one of the two X chromosomes in every cell of the female is inactivated and once this inactivation has occurred in a particular cell, all of its descendants will have the same X chromosome inactivated.
The inactivated female X condenses into a Barr body through modifications on the DNA.
Fact: Many pathways influence the cell by initiating gene expression.
Question: How does cell signaling influence a cell's gene expression?
Pathways lead to a cellular response, and this often is for control of proteins, which carry out the gene expression of a cell!
1. Some pathways activate enzymes that interact with DNA transcription factors and thus affect protein synthesis.
2. Other pathways modify proteins, affecting their activity (often by activating or inactivating them).
In eukaryotes, what does the cell cycle consist of?
A long preparatory period called interphase (G1,S, G2).
The mitotic phase begins with mitosis, which consists of five stages: prophase, prometaphase, metaphase, anaphase, and telophase.
The final stage of the cell division process is cytokinesis.
How does meiosis generate variation in the daughter nuclei?
Meiosis generates variation in the daughter nuclei during crossover in prophase I and random alignment of tetrads at metaphase I.
Across his experiments, Mendel saw a consistent 3:1 ratio of one trait to another when crossing the F1 generation. What four concepts was he able to conclude from this?
1. Alternative versions of genes called alleles account for the observed variations.
2. For each characteristic, an organism inherits one allele from each parent.
3. If the two alleles for the same characteristic differ, the dominant allele determines the appearance whereas the recessive allele is not observed.
4. Law of Segregation: Two alleles for a heritable characteristic separate from each other during gamete formation, and these two alleles end up in different gametes.
What is the impact of males being hemizygous?
Males will display recessive phenotypes even with only one recessive allele as they are hemizygous with only one copy of the X chromosome.
So, while females need both alleles to have the phenotypic results of a recessive trait, men only need one copy of the recessive allele to express it.
What are the four categories of signaling in multicellular organisms?
1. Paracrine signaling: Takes place over short distances/ local signaling. This type releases ligands in high concentrations, but they are short-lasting as they are quickly broken down or reabsorbed into the signaling cell.
Ex: autocrine signaling and neuronal signaling.
2. Endocrine signaling: Carried long distances through the bloodstream. Low concentrations, long-lasting.
3. (Direct signaling) Gap Junctions/ plasmodesmata: Allow small molecules, including signaling molecules, to flow between neighboring cells. The cells are physically in contact!
Where does a loss of control of the cell cycle and cell division begin?
The loss of control begins with a change in the DNA sequence of a gene the codes for one of the regulatory molecules. Then, faulty instructions lead to a protein that does not function as it should.
Describe meiosis I and meiosis II.
Meiosis I: First round of meiotic cell division; referred to as reduction division because the ploidy level is reduced from diploid to haploid. This separates the homologous chromosomes.
Meiosis II: Second round of meiotic cell division; sister chromatids are separated into individual chromosomes, and the result is four unique haploid cells. Separates chromatids into individual chromosomes.
What are the different degrees of dominance?
1. Complete dominance: Heterozygote offspring always demonstrates the phenotype of the dominant parent allele.
2. Incomplete dominance: When the phenotype of a heterozygote looks like a mix of the two parental phenotypes.
3. Codominance: When the two alleles affect phenotype in separate, distinguishable ways.
What do disorders result from, and do we typically see them exist in recessive or dominant alleles?
Disorders result from abnormality/ mutation in one or both alleles of a single genes.
Most harmful alleles are recessive because they would not persist in populations as dominant and generally rare. However, some disorders are caused by dominant alleles such as Huntington's disease
What is a cell-surface receptor, and what are the different kinds of cell-surface receptors?
Cell-surface receptors transmit a signal from outside the cell to the cytoplasm.
1. Ion channel-linked receptors (Ligand-gated ion channel): When bound to their ligands, these form a pore/ channel through the plasma membrane which certain ions can pass. Once the ligand unbinds, the channel closes again.
2. G-protein-linked-receptors: Interact with a G-protein on the cytoplasmic side of the plasma membrane. This promotes the exchange of bound GDP for GTP and allows the G-protein to then interact and activate other enzymes or ion channels to transmit a signal.
3. Receptor kinase receptor: Ligand binding results in phosphorylation, which leads to a response.
4. Nuclear receptor: Rather than the receptor being on the cell membrane, this is on the nuclear membrane.
There are three major checkpoints in the cell cycle. Where are they and what are they?
1. G1 Checkpoint: Occurs near the end of G1. This determines whether the cell has adequate size, sufficient nutrients, and assesses the DNA integrity to ensure there is no damage before the cell enters the S phase ofr DNA replication.
If conditions are unfavorable, the cell will halt the cycle for repair or enter G0!
2. G2/M Checkpoint (Antephase): Occurs at the transition between the G2 phase and mitosis. This verifies DNA replication is complete and that no DNA damage has occurred.
3. M Spindle Assembly Checkpoint: Occurs during metaphase of mitosis. This ensures that all chromosomes are properly attached to spindle microtubules via their kinetochores to ensure accurate chromosome segregation and prevent aneuploidy.
Describe each phase of mitosis.
2. Prometaphase: The nuclear envelope fragments, chromosomes continue to condense and have microtubules attach to their kinetochores, and microtubules attach to other microtubules to form nonkinetochore microtubules.
3. Metaphase: Centrosomes are located at opposite poles in the cell, chromosomes line up along the metaphase plate as the centromeres of each chromosome lie on the plane at the plate, and kinetochores of each sister chromatid pair are attached to microtubules from opposite poles.
4. Anaphase: The cell elongates as the nonkinetochore microtubules lengthen and the two sister chromatids are separated from one another.
5. Telophase: The nucleoli reappear as two nuclei form (the nuclear envelope fragments from the parent cell form around the daughter nuclei) in each pole of the dividing cell, chromosomes start to decondense, spindle fibers are broken apart.
What are three patterns of inheritance?
1. Pleiotropy: when a single gene has more than one phenotypic effect.
2. Epistasis: when the expression of a gene affects the expression of another.
3. Polygenic inheritance: when multiple genes affect a single phenotypic trait (hair, skin, height). Generally, for quantitative characteristics: traits that occur on a gradient/ range.
How do you identify an X-linked dominant trait from a pedigree?
1. There is no generation skip and no carriers.
2. All daughters display the trait if they have fathers that display the trait.
3. All males that display the trait MUST have mothers that display the trait.