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path from genes to proteins
1. Transcription- enzymes use the base sequence of a gene to make a strand of RNA
2. Translation- Information in the RNA strand id decoded (translated) into a sequence of amino acids
3. Central Dogma of DNA to RNA to Protein
Central Dogma of DNA to RNA
1. Replication: DNA is replicated and passes on coded information
2. Transcription: Coded information is passed on to the RNA during transcription
3. Translation: Messenger RNA carries coded information to the ribosome during protein synthesis
4. Proteins provide structure and carry out almost all biological activity
(most abundant RNA in the cell)- Forms ribosomes where polypeptide chains are assembled
RNA (structure and function)
Form: Single stranded
Function: disposable copies of heritable information
DNA (structure and function)
Form: Double-stranded helix
Function:Permanent storage of heritable information
Reading unit for translation machinery during translation
-starting codon is always AUG
-codons specify different amino acids
The Genetic Code
1. Messenger RNA carries DNA protein-building structures to ribosomes
2. Messenger RNA's messgae is written in codons
_Mutations are permanent, small-scale changes in the base sequence of a gene
-Common mutations include insertions, delitions, and base-pair substitutions
(makes exact copies)- the basis of growth, cell replacement, and tissue repair in multicelled organisms
-the basis of asexual reproduction in single-celled and multicelled species
(Only in the context of sexual reproduction)
basis of sexual reproduction
reduces chromosome number by half to produce egg and sperm
-association of DNA, histones, and other proteins
-proteins structurally organize the chromosome and affect access to its genes
1. New cell forms
2. Runs through Interphase
3. Ends when cell reproduces by nuclear and cytoplasmic division
1. cell grows in mass and all cytoplasmic material is duplicated
2. DNA replication duplicates chromosomes
3. The cell prepares for division
Process of Mitosis
(a nuclear division method that maintains the chromosome number)
1. duplicated chromosomes condense and prepare to form chromosomes
2. microtubules form a bipolar spindle
3.Nuclear envelope breaks down
1. Microtubules from one spindle pole harness one chromatid of each chromosome
2. microtubules from opposite poles then harness the sister chromatid
3. chromosomes are lined up in the middle of the cell
1. sister chromatids are detached from one another as the spindles move apart from each other
2. microtubules that overlap puch away from each other and spread the poles further apart
1. two identical clusters reach opposite poles
2. The nuclear envelope forms around each side
3. Both new nuclei have the parental chromosome number
(nuclear division mechanism that precedes gamete formation in Eukaryotic cells and halves the parental chromosome number)
-the first nuclear division
-each duplicated chromosome lines up with its homologous partner
-the two homologous chromosomes move apart, toward opposite spindle poles
-The second nuclear division
- Sister chromatids are pulled away from each other
- Each is now an individual chromosome
The first phase of meiosis I. During prophase I the replicated chromosomes condense, homologous chromsomes pair up, crossing over occurs between homologous chromosomes, the spindle is formed, and the nuclear envelope breaks apart into vesicles. Prophase I is the longest phase of meiosis.
The second phase of meiosis I. During metaphase I the paired homologous chromsomes (tetrads) align at the center of the cell (the metaphase plate).
The third phase of meiosis I. the replicated homologous chromosomes are separated (the tetrad is split) and pulled to opposite sides of the cell.
The fourth of meiosis I. the number of chromosoms is now reduced by half. After this phase the cell is considered to be haploid. Note however, that the chromosomes are still replicated, and the sister chromatids must still be separated during meiosis II.
The first phase of meiosis II. identical to the mitotic step, except that the number of chromosomes was reduced by half during meiosis I.
The second phase of meiosis II. identical to the mitotic step, except that the number of chromosomes was reduced by half during meiosis I.
Variation during Meiosis
1. Crossing over during prophase 1
2. Chromosome shuffling during metaphase 1
3. Chance meeting of gametes at fertilization
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