Chapter 8 Flashcards
Replication, Binary Fission, and Mitosis
All cells divide
-unicellular organisms divide to reproduce
-cell division produces a continuous supply of
replacement cells in multicellular organisms
Sexual life cycle- eukaryotic cells divide by mitosis
-a fertilized egg, or zygote, divides by mitosis
-the fetus grows and develops into a mature adult consisting out countless cells
-mitosis makes cells with identical DNA
Sexual life cycle- eukaryotic cells divide by meiosis
-each mature individual produces sex cells by another form of cell division, meiosis
-meiosis only occurs during reproduction (fertilization)
-meiosis makes gamete cells with unique DNA
Sexual life cycle- gametes fuse during fertilization
-sex cells produced by meiosis contain half the DNA as body cells
-at fertilization, the zygote inherits DNA from both gametes (sperm and egg cells)
What can mitosis allow an organism to do?
-miotic cell division allows an organism to grow and develop, repair tissues, and regenerate lost body parts
-some organisms reproduce asexually by mitosis
Define apoptosis
-cell death
-it’s a process that can carve out distinctive structures during development
-programmed cell death
-normal part of development
-also eliminates damaged or aging cells
-dismantles a cell from the inside out
Define necrosis
-accidental cell death, like a cut or bruise
2 functions of apoptosis
-eliminates excess cells, carving out structures
-weeds out aging or defective cells
Apoptosis is closely regulated
1.) death receptor on doomed cells binds signal molecule
2.) executioner proteins destroy proteins and other remnants
3.) immune system cell engulfs and destroys cell remnants
How fast do you shed skin cells?
-tens of thousands of skin cells shed per minute
How long, on average, does a new cell live?
-an average of 35 days
Define fertilization
-the union of the sperm and egg cell
Define zygote
-the first cell of a new offspring
Define binary fission
-replicates and divides prokaryotic cell’s DNA into 2 daughter cells
Define cytokinesis
-distributes cytoplasm into 2 daughter cells following the division of a cell’s chromosomes
Step 1 in DNA replication is to unwind DNA
-the DNA helix strands unwind/unzip and separate
-enzyme called helicase unwinds the DNA
-single strand binding proteins hold the strands apart/ keep them from rejoining
Step 2 in DNA replication is to bind complementary nuceotides
-RNA primers match up with DNA
-an enzyme celled primase adds a short strand of RNA to each template strand
Step 3 in DNA replication is new strands are synthesized
-DNA polymerase is an enzyme that makes new DNA strands, starting at the RNA primers
Step 4 in DNA replication is nucleotides are added
-each strand is a template that attracts and binds to complementary nucleotides (a>u, g>c, c>g, t>a)
-the RNA primers provide 3’ ends, where the DNA polymerase adds nucleotides
-proof reading activity checks and replaces incorrect bases that were just added
Step 5 in DNA replication is leading strand synthesis is continuous
-on one strand the DNA polymerase follows the helicase as it unzips (leading strand) in a 5’ to 3’ direction
Step 6 in DNA replication is lagging strand synthesis is discontinuous
-on the other strand, DNA polymerase adds nucleotides in the opposite direction from helicase movement (lagging strand)
-they produce DNA in small sections called Okazaki fragments
Step 7 in DNA replication is DNA ligase fills the gaps
-after RNA primer is replaced with DAN, ligase seals the sugar-phosphate backbone
-ligases form covalent bonds between the DNA segments
Define genome
-all the genetic material in an organism
What are the DNA replication proteins?
-helicase
-binding proteins
-primase
-DNA polymerase
-ligase
What does the helicase do?
-unwinds the double helix, to make it ready for replication
What do the binding proteins do?
-stabilize each strand of DNA, making it not join back together
What does the primase do?
-adds short RNA primer to each template strand
-it’s an enzyme
What does the DNA polymerase do?
-binds nucleotides to form new strands, starting at the RNA primers
-also corrects mismatched base pairs in DNA replication
What do ligase do?
-creates covalent bonds between adjacent DNA segment (the sugar-phosphate backbone)
Why do enzymes work at multiple origins of replication?
-each cell contains an enormous amount of DNA, so having multiple origins of replication greatly reduces the amount of time needed for DNA replication
Define chromosome
-a continuous molecule of DNA wrapped around a protein in the nucleus of a eukaryotic cell
-the genetic material of a prokaryotic cell
Define RNA primer
-a short strand of RNA that attracts DNA to initiate DNA replication
DNA polymerase can only add nucleotides to which end?
-only to the exposed 3’ end
Define leading strand
-the strand in DNA replication that is continuously adding nucleotides from 3’ to 5’
-toward helicase
Define lagging strand
-the strand in DNA replication that adds short 5’ to 3’ pieces, each from its own RNA primers in Okazaki fragments
-away from helicase
Prokaryotes divide by binary fission (bacteria and archaea)
-in prokaryotes, reproduction occurs by binary fission, an asexual process that replicates DNA and distributes it to 2 daughter cells
Steps for binary fission
1.) prokaryotes have 1 chromosome (a singular cellular chromosome)
2.) prokaryotes replicate their DNA (as the cell prepares to divide, DNA is replicated and attaches to the inside of the cell membrane)
3.) prokaryotes separate 2 copies (the cell membrane extends and grows between the 2 DNA molecules, partitioning them off
4.) prokaryotes divide into 2 new cells (the cell divides in half, forming 2 daughter cells, each identical to the original)
How many chromosomes do prokaryotic cells have?
-each prokaryotic cells contain one circular chromosome
How fast can bacteria cells divide?
-bacteria cells can divide every 20 minutes
What happens when a cell isn’t dividing?
-the chromatin is loosely packed so the cells can easily access the information in the DNA to produce the proteins it needs
List the parts of a cell from smallest to largest
-nucleotide
-histone
-nucleosome
-chromosome
-nucleus
-cell
Eukaryotes divide by mitosis
-eukaryotes don’t divide by binary fission. instead they divide by mitosis, which is similar but more complex
Replicated chromosome condense before eukaryotic division
-the DNA in the cell on the left is loose (like loose yarn)
-the DNA in the cell on the right has condensed into visible chromosomes (like tightly coiled yarn)
DNA condenses when the cell is dividing
-packaging condenses DNA
-naked DNA wraps histone proteins, forming bead-like structures called nucleosomes
-nucleosomes cluster together in chromatin
-scaffold proteins within chromatin keep it tightly packed
Chromosomes are extra condensed
-after DNA is replicated, discrete chromosomes form
-the highly folded chromosomes take up less space and are easier to move than unwound chromatin
Define chromatin
-a collective term for all the DNA and its associated proteins in the nucleus of a eukaryotic cell
Define nucleosome
-the basic unit of chromatin
-consists of DNA wrapped around histone proteins
Define chromatid
-1 of 2 identical DNA molecules that makeup a replicated chromosome
Define centromere
-a small section of a chromosome where sister chromatids attach to each other
Define centrosome
-structures in a cell that organize the miotic spindles
Define spindle
-a set of microtubule proteins that coordinate the movement of the chromosomes
-aligns and separates chromosomes in mitosis and meiosis
Define kinetochores
-a protein that attaches a chromosome to the spindle in cell division
Define cell cycle
-a sequence of events that occur in an actively dividing cell
-is a repeated series of events
What are the 3 main stages of a cell cycle?
-interphase
-mitosis
-cytokinesis
Define cell plate
-a structure that appears at the midline of dividing plant cells
-cell plate grows and consolidates as vesicles from the golgi apparatus deliver cellulose, proteins, and other polysaccharides
What happens during interphase?
-the cell replicates its DNA and carries out many functions unrelated to cell division (like protein synthesis)
-G1, S, and G2 phases (also G0 phase)
-happens before meiosis and mitosis
-cell is growing
What happens in G1 phase of interphase?
-normal cell function and cell growth
-produces new organelles and other components it will need if it divides
-protein synthesis occurs
What happens in S phase of interphase?
-DNA replication
-cell replicates its entire genome, every chromosome (it’s not committed to divide)
-also repairs damaged DNA
What happens in G2 phase of interphase?
-additional growth and preparation for division
-cell produces proteins that are necessary for mitosis
-DNA winds more tightly around its associated proteins which signals the start of mitosis
What happens in G0 phase of interphase?
-non dividing
-cell continues the function but doesn’t its DNA or divide
-most of your cells are in G0 phase
-nerve cells in brain are permanently, that’s why it doesn’t grow after adult size and brain damage is often irreparable
What are the 5 stages of mitosis?
-prophase
-prometaphase
-metaphase
-anaphase
-telophase
What happens in prophase of mitosis?
-chromosomes and spindle form
-chromosomes condense and become visible
-mitotic spindle forms as centrosomes move to opposite poles of the cell
What happens in prometaphase of mitosis?
-chromosomes attach to the spindle fibers
-nuclear envelope breaks up
-spindle fibers attach to the kinetochores on chromosomes
What happens in metaphase of mitosis?
-chromosomes line up along the equator of the cell (which is called the metaphase plate)
What happens in anaphase of mitosis?
-chromatids separate
-centromeres split as sister chromatids separate and move to opposite poles of the cell (they are now chromosomes)
What happens in telophase of mitosis?
-2 new nuclei form
-nuclear envelope and nucleolus form at each pole
-chromosomes decondense
-spindle fibers disappears
What happens in cytokinesis?
-in animal cells, the cleavage furrow first appears in telophase as an indentation/contractile ring of the cell membrane
-it deepens as a ring of proteins beneath the cell membrane contracts
Define cleavage furrow
-a ring of actin and myosin that split cells in cytokinesis
-works like a drawstring
How fast does miotic cell division happen?
-miotic cell division occurs some 300 million times per minute in your body
How are cancer cells different?
-look different shape wise
-lose specialized features
-some have multiple nuclei
-immortal: ignores “clock” that limits normal cells to 50 or so divisions
-divide uncontrollably
-resist controls over cell division
-high telomerase
Define telomere
-noncoding DNA at the tip of a eukaryotic chromosome
Define telomerase
-an enzyme that extends telomeres, enabling cells to divide continuously
-they add DNA
-cancer cells have high telomerase
Define contact inhibition
-property of most eukaryotic non cancerous cells
-inhibits cell division when cells come in contact with another cell
Define ongiogenisis
-the product/development of new blood cells
Define oncogene
-a gene that normally stimulates cell division when when overexpressed/too active lead to cancer
Define proto oncogene
-mutated or overly active oncogenes
Define tumor suppressor gene
-genes that encodes proteins that block cancer development
-prevents cell division and promote apoptosis
-when inactivated or suppressed cause cancer
What does the G1 phase checkpoint check for?
-it checks to see if the DNA is damaged
-if genetic material is damaged beyond repair, a protein called p53 promotes the expression of genes encoding DNA repair enzymes
-badly damaged DNA prompts p53 to trigger apoptosis, and the cell dies
What does the S phase checkpoint check for?
-it checks to see if the DNA is replicated correctly
-if cell doesn’t have enough nucleotides to complete replication or if a DNA molecule breaks, the cell cycle may pause or stop at this point
What does the G2 phase checkpoint check for?
-has all the DNA been replicated?
-can damaged DNA be repaired?
-is spindle making machinery in place?
-last one before mitosis
-if cell doesn’t contain 2 full sets of identical DNA or if the spindle-making machinery isn’t in place, the cell cycle may be delayed. Alternatively, the p53 protein may trigger apoptosis
What does the metaphase checkpoint check for?
-if the kinetochores are attached correctly to the spindle fibers
-if the chromosomes are aligned at the equator
-if everything checks out, the cell proceeds to anaphase
Define tumor
-an abnormal mass of tissue
-cancerous cells divide out of control and form a mass called a tumor
Define benign tumor
-slow growing
-harmless, unless they become large enough to disrupt nearby tissues or organs
-tough capsule surrounds tumor to prevent it from invading
-capsule of connective tissue that keeps tumor from spreading
-contained
-warts or moles
Define malignant tumor
-can “seed” new tumors throughout the body
-spreadable
-doesn’t have that surrounding capsule to keep it from spreading
Cancer arises when genes are mutated
-mutations alter the function of key cell cycle control genes
-cancer may arise from overactive proto-oncogenes or from underactive tumor-suppressor genes
Cancer risk can vary by ethnicity
-gene mutations such as BRCA1 are inherited, making them more common in particular ethnic groups
-BRCA1 increases the risk of break cancer
What are the traditional cancer treatments?
-surgical tumor removal
-drugs (chemotherapy)
-radiation
What is chemotherapy?
-drugs delivered intravenously to stop cells from dividing
-can selectively kill cancer cells
What is radiation therapy?
-direct streams of energy from radioactive isotopes to kill tumor cells in limited areas
-can selectively kill cancer cells
Define metastasis
-cells can break away from original mass and travel to bloodstream or lymphatic system to colonize the other areas of the body
Define cancer
-class of diseases characterized by uncontrollable division of malignant cells that invade and spread to the other tissues
What is leukemia
-excessive production of the wrong kinds of blood cells
What happens at each cell division?
-at each cell division, telomeres lose nucleotides from their ends (they gradually become shorter)
-after about 50 divisions, the cumulative loss of telomere DNA signals division to stop in a normal cell
Reducing DNA damage reduces cancer risk
-inherited mutations and factors in the environment that damage DNA can increase cancer
-mutations are caused in many ways
What to do to avoid or reduce the risk of cancer
-eat less saturated fats and eat more fruits and veggies
-maintain healthy bodyweight and get regular, vigorous activity
-stop using tobacco, or better yet, never start
-avoid UV radiation from sunlight and tanning beds
-use self tests and medical exams for for early detection
-use condoms to avoid exposure to viruses known to cause cancer
What is the newest approach to cancer treatment that promises to be the most selective?
-immunotherapy
-gene therapy
Define growth factors
-proteins that stimulate/signal cell division
Investigating life: natural selection is a huge challenge in the fight against cancer
-every tumor contains a mix of drug-resistant and susceptible cells that compete for space and nutrients
-in the absence of drugs, resistant cells are at a disadvantage, but the elimination of all drug-susceptible cells by standard cancer therapies give them selective advantage
-adaptive cancer therapies maintain competition between drug-resistant and susceptible cells
Investigating life: experimental results comparing cancer therapies
-in mice receiving cancer therapy, tumors grew quickly after treatment stopped.
-periodically skipping doses delayed but didn’t prevent this outcome.
-in contrast, adaptive therapy (declining drug doses) caused stable tumor size
