Protein synthesis and cell division
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- -occurs in the nucleus
- -the genetic sequence represented by the base triplets in DNA serves as a template for copying the information into a complimentary sequence of codons.
- -Three types of RNA are made from the DNA template
- 1) Messanger RNA (mRNA)- directs the synthesis of a protein
- 2) Ribosomal RNA (rRNA) - joins with ribosomal proteins to make ribosomes
- 3) Transfer RNA (tRNA)- binds to an amino acid and holds it in place on the ribosome until it is incorporated into a protein during translation
- the nucleotide sequence in a mRNA molecule specifies the amino acid sequence of a protein. Ribosomes in the cytoplasm carry out translation.
- 1) An mRNA molecule binds to the small ribosomal subunit at the binding site. A special tRNA called the intiator binds to start the codon on mRNA, where translation begins.
2) next the large ribosomal subunit attaches with the small ribosomal subunit creating a functional ribosome.
3) the anticodon of another tRNA with its attached amino acid pairs with a second mRNA codon at A site of the ribosome
4)A component of the large ribosomal subunit catalyzes the formation of a peptide bond between methionine, which seperates from the tRNA at the P site , and the amino acid carried by the tRNA at the A site.
5) tRNA at the P site detaches, and the ribosome shifts the mRNA strand by one codon. The tRNA in the A site moves to the P site allowing another tRNA with its amino acid to bind to a newly exposed codon at the A site. steps 3 through five repeat
6) protein synthesis ends when the ribosome reaches a stop codon at the A site which causes the completed protein to detach from the final tRNA
the process by which cells reproduce themsleves. two types of cell division. Somatice cell division and Reproductive cell division
Somatic cell division
a cell undergoes a nuclear division called mitosis to produce two identical cells with the same number and kind of chromosomes as the original cells
a cytoplasmic division during mitosis
the two chromosomes that make up each. 23 pairs on inherited from each parent.
sex chromosomes X and Y
are not homologus chromosomes
diploid cells 2n
because somatic cells contain two sets of chromosomes the are called diploid cells
the period between cell divisions; chromosomes not visible under light microscope
G1 phase (somatic cell cycle)
Metabolically active cell duplicates organelles and cytosolic components; replication of chromosomes begins (cells that remain in the g1 phase for a very long time are siad to be in the G0 phase)
Replication of DNA and centrosomes
cell growth, enzyme and protein synthesis continues; replication of centrosomes is complete
Parent cell produces identical cells with identical chromosomes; chromosomes under light microscope
nuclear division; distribution of two sets of chromosomes onto seperate nuclei
Prophase (after G2 phase) start of the actual split
chromatin fibers condense into paired chromatids; nucleolus and nuclear envelope disappear; each centrosome moves to an opposite pole of the cell
Centromeres of chromatid pairs line up at metaphase plate
centromeres split ; identical sets of chromosomes move to opposite poles of cells.
Nuclear envelopes and nucleoli reappear; chromosomes resume chromatin form; mitotic spindle disappears
Cytoplasmic division; contractile ring forms cleavage furrow around centre of cell, dividing cytoplasm into separate and equal portions.
- reproductive cell division that occurs in the gonads (avaries and testes) produces gametes in which the number of chromosomes is reduced by half
- - is the process that produces haploid gametes; it consists of two successive nuclear divisions called meiosis 1 and meiosis 2
contain a single set of 23 chromosomes and thus are haploid
homologus chromosomes undergo synapsis (pairing) and cross-over; the net result is two haploid cells that are genetically unlike eachother and unlike the starting diploid parent cell that produced them
two haploid cells divide to form four haploid cells
- a cells shape is similar to its function
- the almost 200 different types of cells in the body vary considerably in size and shape.
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