D2 Flashcards
What is gene regulation?
Control of the timing, location and amount of genes expressed in an organism. Can lead to cell specialisation, or adaptation to environment
What is a phenotype?
Physical traits resulting from the specific proteins an individual has due to their expressed genes
What is mRNA degradation?
The use of enzymes to break mRNA into nucleotides for recycling. This is done by removing the poly A tail and the GTP cap before breaking the bonds between nucleotides
What are exonucleases?
Enzymes that break down nucleic acids by removing individual nucleotides. Crucial for mRNA degradation
What is epigenesis?
The process of changing the phenotype of a cell without altering the genotype. Driven by internal signalling messages and external environmental cues
What are epigenetic tags?
Chemical modifications to DNA or histones that flag part of a genome to guide gene expression. Can be used to turn on or turn off a gene
What is DNA methylation?
The process of adding a CH3 methyl group to a DNA nucleotide as an epigenetic tag. Often added to the promoter region to prevent transcription and thus expression of a gene.
What is the importance of promoters in transcription?
Promoters are the binding site for transcription factors which allow RNA polymerase to bind. Indicate where new genes begin and regulate on/ off of the genes
What is the importance of transcription factors in transcription?
Transcription factors are proteins that regulate transcription. They can be general or specific (activators or silencers). Allow for precise and efficient regulation of genes.
What is the importance of an enhancer region in transcription?
A region away from the gene that has a binding site for activators to bind to. Allows DNA to form a loop, allowing activators to interact with transcription factors at the promoter to increase the rate of transcription
How can transcription factors be used to initiate transcription?
Activators are a type of transcription factor that can accelerate or promote transcription. Activators bind to enhancers
How can transcription factors be used to prevent transcription?
Repressors are a type of transcription factor that prevent or slow transcription by binding to the silencer region.
How is the length of the Poly A tail a form of gene regulation?
Changing the length of thr Poly A tail can alter the speed of degradation. By increasing the tail length, more of the protein is made before it is degraded, decreased tail length means faster degradation. External signals and chemicals can increase the rate of degradation also.
How does DNA methylation regulate transcription?
Methylation at the promoter region can regulate transcription by inhibiting the binding of transcription factors. Methyl groups can also bind to histones to silence multiple genes.
What is epigenetic inheritance?
Epigenetic inheritance is the process of some epigenetic tags being passed on to offspring. Therefore, the impact of environmental experiences can be passed on
What are primordial germ cells?
Diploid cells that go through meiosis to form gametes. Formed before an organism is born and have most of the epigenetic tags removed
What is epigenetic reprogramming?
The removal of epigenetic tags during the formation of primordial germ cells. This allows the zygote to access the full genome where epigenetic tags can be reprogrammed or edited
What are imprinted genes?
Tags added to genes in the process of becoming gamete cells. A gene that is only expressed/ silenced in one type of gamete (e.g sperm but not egg)
What are differentially methylated regions (DMR’s)?
Regions which have the same DNA base sequence, but different gene expression due to the accumulation of different methylation patterns
What is an operon?
ONLY IN PROKARYOTES. When several related genes share the same promoter. Allows groups of genes to be turned on/ off using an operator site that a repressor can bind to
How is air pollution linked to methylation?
Nitrous oxides and hydrocarbons in air pollution can decrease methylation, causing an increased expression of proteins that regulate the immune system. Causes excess inflammation leading to asthma and heart disease. More significant during pregnancy
Explain the example of ligers and tigeons as an example of epigenetic inheritance
Ligers (BIG)= male lions imprinted gene codes for larger offspring x Tiger (no imprinted gene)
Tigeons (SMALL)= female lions imprinted gene codes for smaller offspring x Tiger
How have monozygotic twin studies helped our understanding of methylation?
Monozygotic twins have the same DNA sequences (genome). But they present with different phenotypes, due to their accumulated methylation patterns over their lifetime
How is glucose used to regulate gene expression?
The presence of blood glucose triggers transcription of the INS insulin gene. The glucose activates the transcription factor, allowing the expression of gene to occur as needed
How is the lac operon regulated by lactose levels in prokaryotes?
Lactose presence allows for the expression of genes related to lactase production. Lactose binds to the repressor site, blocking it and allowing the gene to be transcribed.
What is cytokinesis?
The splitting of the cytoplasm to create 2 daughter cells from one parent cell. Last step of cell division after genetic material has already been divided evenly
What is a cleavage furrow?
The inwards pulling of the plasma membrane at the equator of the cell using a ring of contractile proteins.
What is a cell plate?
A layer of vesicles at the equator of a plant cell that fuse to form the new cell wall
What are chromatids?
Two identical copies of DNA attached to each other by proteins
What is DNA condensation?
The tight wrapping of DNA into linked nucleosomes for transport and division
What is the cell cycle?
The series of events leading up to cell division and cell division. Includes cell growth, DNA replication and preparation of division.
What is interphase?
Preparation for cell division
What is cell proliferation?
The rapid increase in the number of cells. When the rate of cell division is faster than the rate of cell death
What is binary fission?
Replication and separation of circular DNA in prokaryotes
How does cytokinesis differ in plant and animal cells?
Animal cells: inside of cytoplasm contracts using proteins to make a cleavage furrom
Plant cells: cell plate forms from merging vesicles. Perimeter of vesicles forms two membranes and the inside of the vesicles contain cellulose to build new cell wall.
Explain oogenesis as a form of uneven cytoplasm division
Division to form egg cells that have lots of cytoplasm and organelles. Divides unevenly so each round of meiosis results in one large egg cell and three smaller cells called polar bodies.
Explain budding as an example of uneven cytoplasm division
Occurs in yeast. Daughter cell only takes a small amount of cytoplasm and grows over time
What are the purposes of cell division?
- Growth
- Repair
- Replace
What occurs in the G1 stage of interphase?
Growth of cytoplasm and accumulation of proteins and nucleotides
What occurs in the S stage of interphase?
DNA is replicated to make sister chromatids. This is a complex, enzyme mediated process
What occurs in the G2 stage of interphase?
Further growth, replication of organelles and formation of visible centrosomes.
What is the metaphase plate?
An imaginary plate along the centre of the cell.
What is a centrosome?
An organelle made of two centrioles that form the spindle fibres that attach to and move chromosomes
What are kinetochores?
Proteins that form at the centromere of each chromatid. Microtubules attach to them to move chromosomes and separate chromatids
What is mitotic index?
The quantification of the proportion of cells currently dividing. = cells in mitosis/ total number of cells. If high, can indicate cancer
How do the motor proteins interact with microtubules to move chromatids in Anaphase?
Between two microtubules there are motor proteins that pull the microtubules towards opposite poles. This allows the chromosomes to centre at the metaphase plate, and creates the tension required to break cohesin loops and separate chromatids.
What are the key events of prophase?
- Nuclear membrane dissolves and migrates into vesicles
- DNA condenses into visible chromosomes
- Centrosomes form and begin developing microtubules
What are the key events of metaphase?
- Microtubules attach to each centromere (of each sister chromatid) at the kinetochore
- Motor proteins between microtubules move the chromosomes to align with the metaphase plate
What are the key events of anaphase?
- Motor proteins continue to pull and extend the microtubules. The pressure as the centrosomes migrate breaks the cohesin allowing the separation of sister chromatids
- Kinetochores shorten the microtubules which pulls the chromatids to the poles of the cell
What are the key events of telophase?
- Nuclear membrane reforms
- DNA decondenses into loose chromatin
- The pinching of the membrane begins (CYTOKINESIS)
