POL sections 7.1 - 7.3 Flashcards
Cell division
A process by which a parent cell duplicates its genetic material and then divides into two similar cells
Two Strategies of Reproduction
Asexual reproduction and sexual reproduction
Asexual reproduction is __________; offspring are _____
a rapid and effective means of making new individuals common in nature; clones of the parent organism: genetically identical to each other and parent
Mutations
Alterations in DNA sequence caused by environmental factors or errors in DNA replication
Single-celled prokaryotes reproduce by ___________
binary fission
Sexual reproduction
Involves fusion of two specialized cells called gametes
Meiosis
Process of cell division resulting in daughter cells with only half the genetic material of the original cell; usually occurs in diploid cells; increases genetic diversity
Chromosome
Consists of a double-stranded molecule of DNA and associated proteins
Somatic cells
Body cells that are not specialized for reproduction; contain two sets of chromosomes and occur in homologous pairs (one from female parent and the other from male parent)
Homologous pair
Homologs bear corresponding, though not identical, genetic information
Gametes
Contain only a single set of chromosomes; n chromosomes; haploid cell
Zygotes
Contain two sets of chromosomes; 2n chromosomes; diploid cell
Fertilization
Two haploid gametes fuse to form a zygote
Essence of sexual reproduction
Random selection of half of the diploid chromosome set to make a haploid gamete, followed by fusion of two haploid gametes from separate parents to produce a diploid cell
Events that must occur for any cell to divide
Reproductive signals, DNA replication, DNA segregation, Cytokinesis
Reproductive signals
Initiate cell division and may originate from inside or outside the cell
DNA replication
Replication of the genetic material; Each of the new cells will have a full complement of genes to complete cell functions
DNA segregation
Process of distributing the replicated DNA to each of the two new cells
Cytokinesis
Process in which cytoplasm divides to form two cells, each surrounded by a cell membrane and sometimes a cell wall
Binary fission
Occurs in single-celled prokaryotes; process by which cell grows in size, replicates its DNA, and separates the DNA and cytoplasm to two cells
Binary fission: reproductive signals
Environmental conditions and nutrient concentrations
Binary fission: DNA replication
Single chromosome is circular; DNA is threaded through a “replication complex” of proteins near the center of the cell; Begins at ori and ends at ter; Two daughter DNA molecules separate and segregate to opposite ends of the cell
Ori
The site where replication of the circular chromosome starts (the origin of replication)
Ter
The site where replication of the circular chromosome ends (the terminus of replication)
Binary fission: DNA segregation
As replication proceeds, ori move toward opposite ends; DNA sequences adjacent to ori region bind proteins necessary for segregation; active process (ATP is hydrolyzed);it makes use of prokaryotic cytoskeleton to move ori regions and associated proteins (structurally actin, functionally tubin)
Binary fission: cytokinesis
Pinching in of cell caused by contraction of ring of fibers on inside surface of membrane (major component: structurally tubulin, functionally actin); As membrane pinches in, new cell wall materials are deposited, which finally separate the two new cells
Eukaryotic cells: reproductive signals
Unlike prokaryotes, signals are related to the function of the entire organism
Eukaryotic cells: DNA replication
Multiple chromosomes; long strands are threaded through replication complexes; occurs only at a specific stage of the cell cycle
Eukaryotic cells: DNA segregation
More complex because of nuclear envelope and multiple chromosomes; pairs of replicated chromosomes initially attached, become highly condensed, and pairs are then pulled apart
Cell cycle
The period from one cell division to the next
Mitosis
The set of processes in which the chromosomes become condensed and then segregate into two new nuclei; Divided into prophase, prometaphase, metaphase, anaphase, telophase
M phase
Refers to mitosis and cytokinesis
Interphase
Cell nucleus is visible and typical cell functions occur (e.g. DNA replication); has three subphases called G1, S, and G2
G1 phase
Cell carries out specialized functions
S phase
DNA is replicated
G2 phase
Cell prepares for mitosis (synthesizes components of microtubules that will segregate chromosomes
Prophase
Beginning of mitosis, where condensed chromosomes, reoriented centrosomes, and the spindle appear
Sister chromatids
After DNA replication, each chromosome has two DNA molecules
Centromere
Region where chromatids are held together
Kinetochores
Specialized protein structures that assemble on centromeres, one on each chromatid; help with chromosome movement
Karyotype
Number and sizes of the condensed chromosomes; karyotype analysis used to identify organisms and detect chromosomal abnormalities
Humans have ______ chromosomes (___ homologous pairs)
46; 23
Centrosome
Organelle in cytoplasm near nucleus that determines orientation of spindle apparatus; Consists of a pair of centrioles
Centriole
Hollow tube formed by nine triplets of microtubules
Reoriented centrosomes
S: centrosome is duplicated; G2-M: Centrosomes move to opposite ends of nucleus creating “poles”
Spindle
Tubulin dimers from centrosomes aggregate into microtubules that extend into the middle region of the cell; forms during prophase and prometaphase
Three types of microtubules in spindle
Polar microtubules; Astral microtubules; Kinetochore microtubules
Polar microtubules
Overlap in middle of cell and keep two poles apart
Astral microtubules
Interact with proteins attached to cell membrane
Kinetochore microtubules
Attach to kinetochores on chromosomes;
Daughter chromosomes
What sister chromosomes become after separation
Prometaphase
Nuclear envelope breaks down; chromosomes attach to kinetochore microtubules
Metaphase
Chromosomes line up at mid-line of cell (equatorial)
Anaphase
Chromatids separate
Chromosome movement
Kinetochores contain molecular motor proteins like kinesin and dynein (ATP hydrolysis energy); Kinetochore microtubules shorten
Telophase
Nuclear envelope forms; nucleoli appear; chromosomes decompactify; two nuclei in a cell
Cytokinesis in animals
Furrowing of cell membrane; Contractile ring produces a contraction, pinching the cell into two; microfilaments assemble from actin monomers present in interphase cytoskeleton controlled by calcium ions released from storage sites in center of cell
Cytokinesis in plants
Vesicles from Golgi apparatus appear along plane of cell division; fuse to form new cell membrane and cell plate (beginning of new cell wall)
Contractile ring
Composed of microfilaments of actin and myosin, which form a ring on the cytoplasmic surface of the cell membrane; Proteins interact to produce a contraction
Growth factors
Mammals produce a variety of substances that stimulate cell division and differentiation
G1-S Transition; R point; restriction point
Cell will proceed with the rest of the cell cycle and divide
Protein kinases
Class of enzymes that are common in cell signaling
Cyclin-dependent kinases (CDKs)
Catalyze the phosphorylation of target proteins that regulate the cell cycle; activated by binding to protein cyclin
Cell cycle regulator + ATP —->(CDK) Cell cycle regulator-P + ADP
Cell cycle checkpoints
Points of transition between different phases of the cell cycle, which are regulated by cyclins and cyclin-dependent kinases (Cdk’s)
G1, G2 checkpoints
Triggered by DNA damage
S checkpoint
Triggered by incomplete replication or DNA damage
M checkpoint
Triggered by a chromosome that fails to attach to the spindle
After the CDK acts, the cyclin is broken down by a _______
protease
Chain reaction for cell cycle
Growth factor → cyclin synthesis → CDK activation → cell cycle events
