Module 11 Flashcards
Cell Cycle
The series of steps that take place as a eukaryotic cell grows, replicates its DNA, and divides to produce daughter cells.
Mitosis
The separation of replicated chromosomes to produce daughter cells that are genetically identical to the parental cell. Also called karyokinesis.
Circular Chromosomes
DNA in prokaryotes.
Linear Chromosomes
DNA in eukaryotes.
Interphase
The time between two successive M phases. Lasts around 10-14 hours.
Daughter Cell
The cell produced after cell division.
G2 Phase
The second gap phase. Cell prepares for M phase.
G0 Phase
Separate from G1 phase. No active preparation for cell division. Occurs in cells that do not actively divide ex. liver cells.
Template Strand
The strand of DNA used as a guide to synthesize new DNA.
Daughter Strand
The new strand of DNA that is synthesized.
Helicase
Unwinds the parental double helix at the replication fork. Allows a single strand of DNA to be available for complementary base-pairs to be added by DNA polymerase.
Topoisomerase
Works up stream of the replication fork. Changes the supercoiled state of DNA, caused by the unwinding of the double helix at the replication fork.
RNA Primase
Synthesizes a short piece of RNA that is complementary to a sequence of the DNA parental strand. Is needed so the DNA polymerase can add DNA bases to the growing chain.
Lagging Strand
The strand that grows away from the replication fork and synthesizes discontinuously as fragments.
DNA Ligase
Joins the fragments of DNA together by completing the sugar-phosphate backbone of the new DNA.
Origin of Replication
Any point on a DNA molecule at which DNA synthesis is initiated.
Telomere
The ends of the linear chromosomes. 5’ TTAGGG 3’ in humans.
Germ Cells
A reproductive cell that produces gametes (sperm or eggs).
Somatic Cells
A non-reproductive cell and the most common type of cell in the body of a multicellular organism.
Haploid
A cell with one complete set of chromosomes (n).
Binary Fission
The process of cell division in prokaryotes.
Cytokinesis
The division of the cytoplasm into two daughter cells.
M Phase
The time during which the parent cell divides into two daughter cells (includes cytokinesis).
Parent Cell
The original cell before cell division.
G1 Phase
First gap phase. Increase in cell size and protein content. Preparing the cell for S phase. Synthesis and activation of regulatory proteins.
S Phase
The synthesis phase, replication of DNA.
DNA Replication
Duplicating DNA.
Replication Fork
The site where the parental DNA strands separate as the DNA duplex unwinds.
Semiconservative Replication
One strand is from the parent and the other is from the daughter.
Single-Strand Binding Protein
Binds to the single-stranded regions of the parental strands. Prevents the parental strands from coming back together.
DNA Polymerase
Adds bases to the nucleotide strand in the 5’ to 3’ direction. Can also correct mistakes that may occur during replication.
Leading Strand
The strand that grows towards the replication fork and synthesizes continuously.
Okazaki Fragments
The short, discontinuous pieces found in the lagging strand.
Proofreading
The process in which a DNA polymerase can immediately correct its own errors by excising and replacing a mismatched base.
Replication Bubble
A region formed by the opening of a DNA duplex at an origin of replication which has a replication fork at each end.
Telomerase
An enzyme that can extend the ends of the chromosome to address chromosome shortening. Is a ribonucleoprotein (protein-RNA complex). Carries its own primer (template DNA) and has reverse transcriptase activity (RNA —> DNA).
Stem Cells
An undifferentiated cell that can undergo an unlimited number of mitotic divisions and differentiate into any of the large number of specialized cells.
Homologous Chromosomes
Pairs of chromosomes, matching in size and appearance, that carry the same set of genes. One of each pair was received from the mother and the other from the father.
Diploid
A cell with two complete sets of chromosomes (2n).
Centrosome
The microtubule-organizing centers for animal cells. Are duplicated and begin to migrate to opposite poles during prophase. Part of the mitotic spindle.
Apoptosis
Cell death (cell suicide).
Cyclin-Dependent Kinases (CDKs)
Kinases that phosphorylate other proteins whose actions are necessary for the cell cycle to progress. Are always present in the cell and are active only when bound to appropriate cyclin.
Proto-oncogene
The normal cellular gene counterpart to an oncogene, which is similar to a viral oncogene but can cause cancer only when mutated.
Gametes
Sex cells (eggs and sperm).
Nonsister Chromatids
Chromatids of different members of a pair of homologous chromosomes. Although they carry the same complement of genes, they may carry different allele variants.
Reductional Division
Division that reduces the number of chromosomes by half.
Equational Division
Division where the number of chromosomes remain the same.
Chromosome Condensation
The progressive coiling of the chromatin fiber, an active, energy-consuming process requiring the participation of several types of proteins.
Mitotic Spindle
Made of microtubules that pull the chromosomes apart into separate daughter cells.
Cyclins
Regulatory protein subunits of specific protein kinases. Their levels rise and fall with each turn of the cell cycle. Directly impacts CDK.
Checkpoint
One of multiple regulatory decision points that determines progression through the cell cycle based on completion of necessary preparatory steps or availability of required resources of signals.
Oncogene
Cancer-causing genes.
Tumour Suppressor
Proteins whose activities inhibit cell division (ex. p53).
Bivalent
Two pairs of sister chromatids (the whole unit).
Chiasma
The crosslike structures formed during crossing over.
Meiosis
To produce daughter cells with exactly half as many chromosomes as the parental cell. Used in sexual reproduction to produce sperm and egg cells. Has one round of DNA synthesis and two rounds of cell division.
Centromere
Holds the chromatids together.
Sister Chromatids
Two identical copies of DNA.
Kinetochores
The protein complex that assembles at the centromere of a chromosome to which spindle fibers attach. The two protein complexes associated with each centromere (one per chromatid) which forms the site of attachment for a single microtubule.
Synapsis
The aligned and precise pairing of homologous chromosomes in prophase I of meiosis.
Cell Division
The process in which a cell can make more cells.
Why Does Cell Division Occur?
1) Cell Growth
2) Cell Replacement
3) Cell Healing
4) Cell Reproduction
Binary Fission Process
1) Proteins bind the circular genome to the inner surface of the plasma membrane.
2) DNA replication starts at a certain spot on the molecule and travels around the circle in opposite directions.
3) Two DNA molecules are produced both of which are affixed to the cell membrane.
4) The two DNA attachment sites separate as the cell elongates during binary fission.
5) A constriction (narrows/tightens) forms at the midpoint of the cell when it is about twice its original size and the DNA molecules are well-separated.
6) At the location of the constriction a new membrane is created and a new cell wall is created (this produces two daughter cells that are identical to the parent cell).
Genome
The genetic material of an organism.
Kilobase (kb)
A thousand base pairs.
Megabase (Mb)
Million base pairs.
Gigabase (Gb)
Billion base pairs.
Nucleoid
A circular bacterial genome with multiple loops held together by proteins.
Chromatin
DNA protein complex.
Nucleosome
When eukaryotic DNA is wrapped around a group of histone proteins.
Histone
Proteins in which DNA wraps around twice.
The Trombone Model
The looping of one of the strands of DNA (the lagging strand).
Circular Chromosome Replication Features
1) There is a single origin of replication.
2) Replication proceeds in both directions until the replication forks meet and fuse on the opposite side. This completes one round of replication.
Prophase (Mitosis)
Stage 1 of mitosis. Characterized by the appearance of visible chromosomes.
Prometaphase (Mitosis)
Stage 2 of mitosis. The nuclear membrane breaks down and the microtubules of the mitotic spindle attach to the chromosomes.
Metaphase (Mitosis)
Stage 3 of mitosis. The chromosomes line up in the center of the cell.
Anaphase (Mitosis)
Stage 4 of mitosis. The centromere divides and kinetochore microtubules shorten. This pulls the chromatids apart toward the centrosome (ensures that one chromatid from each pair goes to opposite poles).
Telophase (Mitosis)
Stage 5 of mitosis. The complete set of chromosomes arrives at a spindle pole and cytosolic changes occur in preparation for the cell’s division. The microtubules of the mitotic spindle break down and disappear. The nuclear envelopes begin to re-form around each set of chromosomes and chromosomes decondense.
Contractile Ring
A ring of actin filaments that forms on the inner face of the cell membrane during cytokinesis. Forms at the equator of the cell perpendicular to the axis of what was the spindle. The ring contracts (pinches the cytoplasm of the cell) and divides it into two daughter cells.
Phragmoplast
Formed in the middle of the cell during telophase. Consists of overlapping microtubules which guide vesicles containing cell-wall components to the middle of the cell.
Cell Plate
During late anaphase and telophase the vesicles fuse to form a new cell wall in the middle of the dividing cell.
Prophase I (Meiosis I)
Stage 1 of meiosis I. Each chromosome has become two sister chromatids held together at the centromere. Homologous chromosomes pair with each other (in the process called synapsis). Chromatids attached to different centromeres (nonsister chromatids). Crossing over happens which allows homologous chromosomes of maternal and paternal origin to undergo an exchange of DNA segments. A random process which results in completely unique chromosomes when completed. No nucleotides are gained or lost in this process.
Meiosis I
A reductional division (the number of chromosomes is halved).
Meiosis II
Often called equational division.
The Oocyte (Egg)
One cell from meiosis II that has most of the cytoplasm.
Cell Cycle Events
1) Initiation of DNA replication (G1/S Transition).
2) Initiation of mitosis (G2/M Transition).
Cyclin Levels (G1 Phase)
The levels of cyclin D and E rise and activate CDKs which prepares the cell for S phase.
Cyclin Levels (S Phase)
Cyclin A levels increase activating CDKs that initiate DNA synthesis.
Cyclin Levels (G2 Phase)
The levels of cyclin B rise activating CDKs that initiate multiple events associated with mitosis (the breakdown of the nuclear envelope in prometaphase and the formation of the mitotic spindle).
DNA Damage Checkpoint
Checks for damaged DNA before it enters S phase.
DNA Replication Checkpoint
Checks for the presence of unreplicated DNA at the end of G2 before the cell enters mitosis.
Spindle Assembly Checkpoint
Checks that all of the chromosomes are attached to the spindle before the cell progresses with mitosis.
Roles of Apoptosis
1) For developing embryo it allows for remodelling of tissues. Ex. a developing hand looks like a paddle until cells are selectively killed.
2) Maintenance of tissue size (eliminate excess cells to balance excess cell growth).
3) Elimination of specific cells (ex. removal of activated T lymphocytes that are no longer required).
4) Elimination of genetically damaged cells (cells that are irreparable need to be removed).
Cancer
A group of diseases characterized by uncontrolled cell division.
Key Features of Cancer Cells
1) Ability to divide on their own without growth signals.
2) Resistance to inhibitory or cell death signals.
3) Ability to invade tissues (metastasis).
4) Promote new blood vessel formation (angiogenesis).
Metaphase Plate
Center of the cell.
Prometaphase I (Meiosis I)
The nuclear envelope breaks down and the meiotic spindles attach to kinetochores.
p53
Often called the guardian of the genome. Stops the transition from G1 to S phase to give time for the cell to fix the DNA.
Bax Protein
p53 stimulates the transcription of the Bax gene which codes for this protein. They bind together to form Bax dimers. The increase of Bax/Bax dimers activates the pathway for programmed cell death (apoptosis).
Bcl-2 Protein
p53 represses transcription of the Bcl-2 gene which codes for this protein.
