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chemical composition of DNA
  • A sugar – deoxyribose
  • Nitrogenous base (there are 4) – thymine (T), cytosine (C), adenine (A), guanine (G)
  • Phosphate group – (PO4-2)
Chemical composition of RNA
  • A sugar – ribose
  • Nitrogenous base (there are 4) – uracil (U), cytosine (C), adenine (A), guanine (G)
  • Phosphate group – (PO4-2)
Chromosome
is a structure containing DNA that physically carries hereditary information; the chromosome contains the genes.
Gene
sequence of nucleotides that stores the information for the synthesis of a protein
Genome
all the genetic information in an organism (or cell)
Phenotype
specific physical characteristic displayed by the organism
Genotype
genetic information contained in DNA of an organism
DNA Replication
used to duplicate the DNA in the cell chromosome before cell division
Step 1 of DNA replication
Two DNA strands unwind (by breaking hydrogen bonds between bases of opposite strands); Strands separate and bases are exposed; this step is catalyzed by DNA gyrase and DNA helicase
Step 2 of DNA replication
Nucleotides free in the cytoplasm base-pair to the exposed nucleotide on the parental strand by forming hydrogen bonds (complementary base pairing)
Step 3 of DNA replication
covalent bonds are formed between the sugar and phosphate groups of adjacent nucleotides (links them); this step is catalyzed by DNA polymerase which synthesizes DNA, proofreads and repairs DNA
semi-conservative replication
End product of DNA replication consists of one of the original strands of DNA and one of the newly synthesized DNA strands
where within the cell does DNA replication occur in procaryotes and eucaryotes
  • Procaryotes – within the cytoplasm
  • Eucarytoes – within the nucleus
DNA proofreading enzymes
DNA polymerase – examines the newly synthesized DNA strand for any errors and corrects any that are found
Transcription
making a mRNA copy of DNA
Step 1 of Transcription
Unwind the two DNA strands where the gene is located; only the part of DNA that contains the gene being copied will unwind, rest of it stays tightly wound
Step 2 of Transcription
Only one of the strands is copied (transcribed), the DNA coding strand; using the coding strand as a template, base pairing occurs using RNA nucleotides; covalent bonds are formed between adjacent RNA nucleotides
Step 3 of Transcription
RNA separates from DNA and DNA rewinds; all of these steps are catalyzed by RNA polymerase
RNA polymerase
binds to a sequence of DNA just in front of the gene to be copied (transcribed) called the promoter (the start sequence); RNA polymerase stops transcribing the gene when it reaches the terminator (the stop sequence)
Coding & Non-coding Strands
  • Coding strands – called exons, it is a stretch of DNA in a gene that contains the information about the amino acid sequences
  • Non-coding stands – called introns, it is a stretch of DNA contained in a gene that does not contain information about amino acid sequences
  • Only eukaryotic genes have introns and exons
where within the cell does transcription occur in procaryotes and eucaryotes
  • Procaryotes – within the cytoplasm
  • Eucaryotes – within the nucleus
Translation
using the information in mRNA to synthesis a protein
Step 1 of Translation
Initiation: mRNA binds to the ribosome and tRNA brings the first amino acid to the ribosome; mRNA binds to the ribosome at the start codon, protein synthesis always starts with methionine (Met)
Step 2 of Translation
Elongation: synthesis of polypeptide involves sequential addition of amino acids to the growing polypeptide chain; ribosome moves down the mRNA matching tRNA anticodons with mRNA codons which repeats over and over until termination
Step 3 of Translation
Termination: protein synthesis is complete; ribosome reaches the stop codon on mRNA, the newly synthesized polypeptide released from ribosome, mRNA released from ribosome
Ribosome
site for protein synthesis in the cell
rRNA
is the RNA component of the ribosome and is essential in protein synthesis, composed of rRNA and proteins
tRNA
it brings the correct amino acid to a ribosome during protein synthesis
mRNA
messenger RNA that conveys the genetic information from DNA to the ribosome where it will be used to synthesis a protein
Codons
sequence of nucleotides in mRNA that are arranged into groups of three that represents a specific amino acid
Genetic code
is a set of rules which determines how nucleotide sequences of mRNA are converted into the amino acid sequences of proteins
where within the cell does translation occur in procaryotes and eucaryotes
  • Procaryotes – within the cytoplasm
  • Eucaryotes – within the ribosomes free in the cytoplasm or the ribosomes attached to the rough endoplasmic reticulum
Mutation
permanent change in the base sequence (genetic material) of DNA
Why can mutations change phenotype?
Mutations can cause a change in phenotype because they alter the organisms DNA. The altered DNA could then cause that mutation to be expressed physically.
UV radiation
Exposure to ultraviolet light causes adjacent thymines to become cross-linked, forming a thymine dimer and disrupting their normal base pairing
Operon
is a special arrangement of prokaryotic genes that play a role in gene expression; it regulates genes that are turned on only when the protein they code for is needed; consists of a promoter, an operator, and structural genes
Structural genes
are the genes which code for a protein
Promoter
regulatory gene, it is a DNA sequence close to the structural genes where RNA polymerase binds and begins transcription of the structural genes of the operon
Operator
regulatory gene, it is a DNA sequence close to the promoter where a repressor protein can bind to prevent transcription
What is the advantage of the bacteria that have an operon?
It helps the bacterium save energy by not making enzymes it doesn’t need at that time. For example; when lactose is missing from the E. coli environment, it won’t waste energy making the enzyme to break it down. Only when lactose enters the environment will it make the enzyme.
Recombinant cell
an organism or cell that has undergone recombination of its genes on a chromosome
Transformation
Naked DNA from a dead or lysed bacteria is transferred in solution to a recipient cell; requires that the donor and recipient be closely related and DNA must pass through cell wall and cell membrane of recipient but this is often impossible; important in the field of genetic engineering
Plasmids
small circular piece of double stranded DNA that is separate from the chromosome; examples of genes found on the plasmid are genes for bacterial toxins and genes for resistance to antibiotics
Conjugation
direct transfer of genetic material between two bacterial cells that are temporarily joined together
Pilus
a cytoplasmic bridge or conjugation bridge
F factor (plasmid)
contains genes for production of sex pilus and transfer of the plasmid
F+
DNA donor; cell that has a plasmid and can transfer a copy to another bacteria cell
F-
DNA recipient; cell that does not contain a plasmid but can receive a copy from another bacterial cell
R factor (plasmid)
a plasmid that contains genes for antibiotic and heavy metal resistance; a copy of the plasmid can be transferred to a bacterial cell that doesn’t contain the resistance genes in turn giving it the genes for antibiotic resistance
Transduction
bacterial DNA transferred between bacterial cells via viruses
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