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Chapter 16-17 (Concept 16.2 (DNA Replication and Repair (Replication:…
Chapter 16-17
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Concept 16.1
Genetic Material
- Transformation - a change in genotype and phenotype due to assimilation of external DNA by a cell (a nonpathogenic strain can become pathogenic through DNA or cell mixing)
- Bacteriophage - viruses that infect bacteria (bacteria-eaters)
- Virus - DNA enclosed in a protective coat and in order to reproduce, they must infect a cell and take over the cell's machinery
- E. coli - a bacteria that normally lives in the intestines of mammals and is generally the bacteria used for infection by phage T2.
- Tests were performed by scientists and it is proven that DNA is what causes infection in cells and when it is injected by phages, genetic information is carried to produce new viral DNA and proteins
DNA
- DNA and proteins are two chemical components of chromosomes and are leading candidates for genetic material
- Proteins are a strong class of macromolecules and are required for hereditary material
DNA was understood but a discovery of 3D structure of DNA needed to surface.
- Double helix - composed of two DNA strands
- Two sugar phosphate are antiparallel and run in opposite directions
The overall shape of DNA:
- side ropes represent sugar-phosphate backbone
- rungs are nitrogenous base pairs, which are held together by hydrogen bonds
- DNA is known as the polymers for nucleotides (phosphate group, sugar, and nitrogen base)
There are four bases linked with DNA: Adenine (A), Thymine (T), Guanine (G), or cytosine (C).
Chargaff's Rule of Base Equivalence:
1) DNA base composition varies between species
2) for each species, the percentages of A and T , and C and G bases are roughly equal
Adenine and Guanine are purines, nitrogenous bases with two organic rings. Cytosine and Thymine are pyrimidines, nitrogenous bases with one organic ring. The double helix worked by pairing a purine with a pyrimidine.
Each base has chemical side groups that can form hydrogen bonds with their corresponding partner. Purines can form two, pyrimidines can form three.
Concept 17.3
Modifying RNA
During RNA processing, both ends of the primary transcript are altered. The 5' end is synthesized first and receives a 5' cap - a modified form of guanine added after transcription. The 3' end is modified before exiting the nucleus. Poly-A tail - formed by enzyme adding adenine at the 3' end
5' cap and poly-A tail both:
1) facilitate exporting of mRNA from nucleus
2) help protect mRNA from degradation by hydrolytic enzymes
3) help ribosomes attach to 5' end
- Introns - noncoding segment of nucleic acid; intervening sequences; generally tRNA
- Exons - coding segments; expressed by amino acid sequence; pairs of 3 make amino acid; codon; mRNA
RNA splicing - process where pre mRNA is transformed to mature mRNA. Introns (non codon) are removed and cut out, while exons (codon) are joined together
- Spliceosome - large complex made of proteins and small RNA, which removes introns
Ribozymes - RNA molecules that function as enzymes; intron RNA function as a ribozymes
1) since RNA is single-stranded, a region may base-pair with any region elsewhere in the same molecule
2) like amino acids, some bases in RNA contain functions that participate in catalysis
3) for RNA to hydrogen bond with other nucleic acid and molecules adds to its catalytic activity
- Alternative RNA splicing - process of producing differential combinations of exons of the same gene
- Domains - structural region in protein; includes active sites of enzymes or enzyme binding to cell membrane
- Exon shuffling - molecular mechanism for the formation of new genes; two or more different exons can be brought together to create new structure
Concept 16.3
Chromosome DNA
- Chromosomes - what makes up the DNA and these structures carry the genetic information
- Chromatin - complex of DNA protein, chromosomes densely packed to fit in the nucleus
- Bacterial chromosome (prokaryotic) - one double-stranded, circular DNA molecule associated with small amounts of proteins
- Eukaryotic chromosome - one linear DNA molecule associated with large amounts of proteins
- Histones - proteins responsible for the first level of DNA packing; over one-fifth of a histone's amino acid is positively charged and it binds to the negatively charged DNA
- Nucleosomes - each single bead on the line of string, or linker DNA; basic unit for DNA packing; sequences around eight histone proteins
- Looped Domains - fiber is formed into these loops which attach to chromosome scaffold composed of proteins
- Heterochromatin - firmly packed form of chromatin and are genetically inactive
- Euchromatin - loosely packed form of chromatin and are genetically active
Concept 17.1
Genes
- Gene Expression - process DNA directs the synthesis of proteins
- One Gene - One Enzyme Hypothesis - theory that each gene directly produces a single enzyme, which consequently affects an individual step in a metabolic pathway
- One Gene - One Polypeptide - modified when it was realized that genes also encoded non-enzyme proteins and individual polypeptide chains
Two Stages for coding DNA to proteins:
- Transcription - synthesis of RNA using information in the DNA; DNA strand during DNA replication also serves as a template for RNA; (any kind of synthesis of RNA on DNA template)
- Translation - synthesis of polypeptide using the information mRNA. Cell must translate nucleotide sequence of mRNA into amino acid sequence.
Bridge between DNA and protein is RNA. RNA - similar to DNA except it contains ribose and uses nitrogen base uracil instead of thymine. Nucleic acids and proteins are polymers with specific sequences of monomers and contain information written two ways: DNA and RNA
In prokaryotes, these stages occur in the cell. In eukaryotes, transcription occurs in the nucleus, while translation occurs in the cytoplasm.
- mRNA - carries genetic messages from the DNA to protein synthesizing machines
- Ribosomes - sites of translation, which are molecular complexes that facilitate the orderly linking of amino acids into polypeptide chains
DNA ----- RNA ----- Protein
- Not all enzymes are proteins
- Many proteins are constructed from two or more polypeptide chains
- Alternative splicing - process that enables a messenger RNA to direct synthesis of different protein variants that may have different cellular functions or properties
Genetic Code
There are only 4 base pairs to complete the set of 20 amino acids.
- Triplet code - flow of information from gene to protein; genetic instructions of polypeptide chain written in DNA
- Template strand - strand that is transcribed, providing a template for the sequence of nucleotides in RNA transcript
- mRNA is complementary to DNA. These pairs are the same in replication except it U substitutes for T in RNA to pair with A
- Codons - mRNA nucleotide triplets paired with DNA
- Reading frame - dividing the sequence of nucleotides in a nucleic acid molecule into a set of consecutive, non-overlapping triplets
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