Biology Lecture Exam #3 Review a. C3 plants (from 3-PGA – 1st organic product formed) 1) gets CO2 directly from air 2) keeps stomata open except on hot, dry days 3) photorespiration occurs on hot, dry day when stomata are closed a) CO2 levels in the leaf increase b) O2 levels increase for a period of time c) rubisco can bind to O2 when CO2 is scarce d) no sugar is produced and growth is slowed 4) plant examples: rice, wheat, soy beans b. C4 plants (from 4 carbon compound formed 1st) VIII. Reproduction and Inheritance: Cellular Basis (Part 1) A. Types of Reproduction 1. Asexual Reproduction a. offspring is genetically identical to the parent b. common in single-celled organisms 1) examples: Paramecium and Amoeba 2. Sexual Reproduction a. produces a unique combination of genes 1) Each parent contributes genes to their offspring 2) this makes offspring genetically diverse 3) genetic diversity is important for evolution B. Cell Theory 1. Cells arise only from pre-existing cells 2. Cells reproduce some cells by dividing a. functions of cell division: 1) growth – produces a multicellular adult from a single-celled embryo 2) replacement – replaces cells that are dead or damaged 3) reproduction – sexual reproduction produces eggs and sperm C. Reproduction in Prokaryotes and Eukaryotes 1. Prokaryotes reproduce by binary fission: a. duplication of the chromosome (the chromosome is smaller than in eukaryotes) b. separation of the duplicated chromosomes c. division into 2 daughter cells, which are identical to one another 2. Eukaryotes a. have large chromosomes 1) the human chromosome is 2” in length uncoiled 2) all the DNA in a single human cell, if uncoiled, is 6 feet long 3) each chromosome contains 1000s of genes (25,000 approx. total in humans) b. have complex chromosomes 1) made up of chromatin, which is composed of: a) 60% protein, including the histones (which the DNA wraps around) b) 35% DNA (each gene is just a piece of the DNA) c) 5% RNA c. chromosomes in diploid and haploid cells 1) diploid (2n) – has two complete sets of chromosomes, one from each parent; diploid cells are found in somatic cells(body cells not including sex cells)
2) haploid (n) – has one complete set of chromosomes; the gametes (egg and sperm) are haploid d. examples of specific numbers of chromosomes in organisms 1) humans – 46 2) chickens – 78 3) tomato – 24 4) mosquito – 6 5) this number is always even D. Cell Cycle 1. Stages a. Interphase – the longest stage of the cell cycle, consisting of 3 substages; 90% of the time involved in the cell cycle is spent here 1) G1 2) S 3) G2 b. (M phase) c. division time (typical human cell) 1) one complete cycle: 24 hours 2) G1: 5-6 hours 3) S: 10-12 hours 4) G2: 4-6 hours 5) M: 1 hour d. cytokinesis 1) separation of the cytoplasm 2) produces 2 daughter cells 3) in plants, a cell plate forms between the cells 4) in animals, a cleavage furrow forms between the cells 2. cells then differentiate (specialize to become blood cell, skin cells, etc.) E. Mitosis 1. Prophase a. chromosomes condense and consist of: 1) 2 sister chromatids 2) centromere – a specialized region where the chromatids are most closely attached 3) kinetochores – granules within the centromere made of specialized protein; there are 2 per centromere and each occur on opposite sides of the centromere b. nuclear membrane breaks down c. nucleoli disappear d. mitotic spindle begins to form, which is composed of: 1) centrosome – a nonmembranous organelle with a microtubule-organizing center 2) long microtubules 3) asters – a radial array of short microtubules 4) centrioles – made up of 9 sets of microtubules, each set having 3 microtubules; are arranged in a ring 2. Prometaphase a. the nuclear envelope fragments b. the long microtubules extend to the center of the cells c. some of those microtubules will attach to the kinetochores and become kinetochore microtubules, which then jerk the chromosomes back and forth 3. Metaphase a. nuclear membrane is completely gone now
b. sister chromatids line up at the metaphase plate after the kinetochore tugging with the centromeres on the metaphase plate c. non-kinetochore microtubules, or polar microtubules, growing from 1 pole of the cell interact with those growing from the other pole d. this stage lasts about 20 minutes 4. Anaphase a. sister chromatids separate b. polar microtubules lengthen the cells c. kinetochore microtubules depolymerize (shorten), releasing tubulin subunits 1) motor proteins “escort” the chromosomes to the poles 2) movement is with the centromeres first d. shortest stage; lasts only a few minutes e. ends with the equivalent and complete collection of chromosomes at the poles 5. Telophase a. chromosomes become less condensed b. nuclear envelope reforms from fragments of the parental nuclear envelope c. 2 genetically identical daughter nuclei form d. nucleolus reappears e. spindle fibers disassemble f. mitosis is now over F. Factors that Affect Cell Division 1. Anchorage dependence – cells must be in contact with a substratum (e.g. extracellular matrix or the inside of a culture container) in order to divide 2. Density-dependent inhibition – cells growing in a culture dish form a single layer and usually stop dividing when they touch each other a. if they are taken out of this layer, they will start dividing again; analogous to injuring your skin and the repair process which ensues 3. Growth factors – proteins can stimulate cells to divide; normal cells do not divide unless they receive a signal from a growth factor to continue growing a. growth factors manage the cell cycle control system G. Cell Cycle Control System 1. Normal functioning a. Checkpoints where cell division arrested unless being given a proceed signal: 1) G1 – seems to be the most important; if no go-ahead is given, cycle goes to the G0 (nondividing) phase 2) G2 3) M b. signals 1) intracellular signals – indicate whether or not a cellular process has been completed a) examples: Has the DNA been duplicated? Have the organelles been duplicated? 2) extracellular signals a) growth factors tell the cell to move on to the next step (1) signals are relayed via the signal transduction pathway to the interior of the cell (2) 50 different growth factors have been discovered thus far c. a normal cell will divide ONLY if it gets a “yes” at all signal checkpoints 1) some mature cells (which usually do not divide in an adult) are arrested permanently at the G! checkpoint (i.e. neurons and muscle cells) 2. Abnormal functioning (failure to control the cell cycle; the basis of all cancers) a. cancer cell behavior 1) no density-dependent inhibition
2) no anchorage dependence 3) can divide without receiving a signal from a growth factor 4) will continue to divide almost indefinitely b. cancer cell terminology 1) benign tumor – mass of essentially normal cells 2) malignant tumor – mass of cancer cells 3) metastasis – spread of cancer from the original site
Bonus questions: (Know the spelling of all of these answers!)