reproduction
organisms have a drive to preoduce (pass on their genes to the next generation
two ways of reproduction
- sexual reproduction
2. asexual reproduction
sexual reproductino
fertilization of an egg by a sperm (multicellular organisms)
many eukaryotic cells reproduce sexually
by fertilization of an egg by a sperm, 1. organisms produce replicates with a wide range of variation and 2. variation helps the species survive through all kinds of environmental changes
asexual reproduction
organismas divide in half making two exacct duplicates (single celled organisms)
binary fission
dividing in half; done in asexual reproduction
- chromosomes (DNA) are duplicated and migrate to oppostie sides of the cell
- cell divides in two (each cell is an exact duplicate of each other)
reasons cells reproduce themselves
- enable a multicellular organism to grow to adult size
- replace worn out or damaged cells
- add new cells (ex: more muscle as a result of exercise)
- reproduction of the species (meiosis)
chromosomes
gene-carrying structure found in the nucleus (gene)
before cells replicate that duplicate their dna
when chromosomes duplicate, the two exact duplicates are attache at the centromere forming sister chromatids
gene
a discreet unit of heredity
chromatin
what chromosomes are called in uncondensed form (most of the time)
human cells carry around ___ genes on ___ chromosomes
25,000, 46
karyotype
a set of chromosomes for an individual in pairs
cell cycle
the time between cell division
1. interphase
interphase
most of the time; variable length of time, cell is doing its "job"; s-phase (synthesis phase when dna is synthexized which means it is duplicated or replicated); g phasees (gaps); m-phase (mitosis when the cell is dividing) cell is active, doings its job chromosomes in chromatin form preparation for cell division see slides
prophase
- chromatin fibers coil up and chromosomes are visible (sister chromatids joined at centromere
2 nuclear envelope begins to break up - mitotic spindle begins to appear
metaphase
- mitotic spindle is fully formed
- sister chromatids brought to the center of the cell, along an imaginary equator (microtubules are pulling from each side, bringing chromosomes to the middle)
mitotic spindle
“spoke-like” microtubules that attach to chromosomes at centromere
anaphase
- some microtubules shorten, pullin sister chromatids apart (moving them toward opposite poles)
- other microtubules lengthen ushing cell poles apart (elongating the cell)
telophase
begins when the two sets of chromosomes reach opposite cell poles (two sets of nuclei)
- spindle disappears
- nuclear envelopes begins to reform
- chromosomes begin to uncoil going back into chromatin form
cytokinesis (in animal cells)
cell divides in two
- cleavage furrow forms
- microfilaments contract (like pulling drawstrings ; two daughter cells with the exact duplicate dna)
cancer
a disease where cells within the organism are dividng out of control (over 200 types exist); the cancer cells keep dividing because they ignore the signals that usually tell them to stop dividing
tumors/cancer grow from a single cell
tumor
an abnormal mass of cells; starts from a single cell
contact inhibition
a control mechanism where normal animal cells stop dividing when they come in contract with other cells; signal are released “telling” the cells to stop dividing
benign tumors
abnormal mass of essentially normal cells; not as dangerous, generally speaking
- do not invade other tissue
- stay in their original place
- can often be completely removed by surgery (unless they are growing in certain organs such as the brain or pancreas)
malignant tumors
cancerous tumors; cells have changed to become more dangerous
- can invade neighboring tissue
- can spread to other parts of the body (metastasis)
- can be very hard to remove by surgery since they often have spread into neighboring tissue
