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Chapter 16 and 17 (Gene Expression: From Gene to Protein (Concept 17.4…
Chapter 16 and 17
Gene Expression: From Gene to Protein
Concept 17.1 Genes specify proteins via transcription and translation
Basic Principles of Transcription and Translation
transcription
synthesis of RNA using information in the DNA
mRNA
carries a genetic message from DNA to the protein-synthesizing machinery of cell
Translation
synthesis of polypeptide using information in mRNA
primary transcript
initial RNA transcript from any gene including specifying RNA that is no translated into protein
Codons: Triplets of Nucleotides
template strand
provides the pattern or template for the sequence of nucleotides in an RNA transcript
codons
mRNA nucleotides triplets written from 5' to 3'
triplet code
genetic instructions for a polypeptide chain are written in the DNA as series of nonoverlapping, three nucleotide words
coding strand
nontemplate DNA strand
Concept 17.2 Transcription is DNA-directed synthesis of RNA
Molecular Components of Transcription
terminator
sequence that signals the end of transcription
transcription unit
stretch of DNA down-stream from the promoter that is transcribed into RNA molecule
promoter
DNA sequence where RNA polymerase attaches and initiates transcription
RNA polymerase
pries two strands of DNA apart and joins together RNA nucleotides complementary to the DNA template strand
Concept 17.3 Eukaryotic cells modify RNA after transcription
Split Genes and RNA Splicing
introns
noncoding segments of nucleic acid that lies between coding region
exons
usually translated into amino acid sequences
RNA splicing
large portions of RNA molecules are removed and the remaining portions are reconnected
slicepsome
removal introns is accomplished by large complex made of proteins and small RNAs
Concept 17.4 Translation is RNA directed synthesis of polypeptides
tRNA
function is to transfer an amino acids from cytoplasmic pool of amino acids to growing polypeptide in a ribosomes
aminoacyl-tRNA synthetase
correct matching up of tRNA and amino acid is carried out by a family related enzymes
rRNA
are transcribed and the RNA is processed and assembled with proteins imported from cytoplasm
P site
holds tRNA carrying the growing polypeptide chain
A site
holds the tRNA carrying the next amino acid to be added to the chain
E site
holds the tRNA and mRNA in close proximity and positions the new amino acid to be added to carboxyl end of growing polypeptide
Concept 17.5 Mutations of one or few nucleotides can affect protein structure and function
substitutions
nucleotide-pair substitution
replacement of one nucleotide and its partner with another pair of nucleotides
silent mutation
has no observable effect on the phenotype
missense mutations
substitutions that change one amino acid tot another one, such mutation may have little effect on the protein
nonsense mutations
causes translation to be terminated prematurely, causing the resulting polypeptide will be shorter than the polypeptide encoded by the normal gene
Insertions and Deletions
are additions or losses of nucleotides pairs in a gene
frameshift mutation
occurs when the number of nucleotides inserted or deleted is not a multiple of three
The Molecular Basis of Inheritance
Concept 16.2 Proteins work together in DNA replication and repair
The Basic Principle: Base Pairing to a Template Strand
semiconservative model
two strands of parental molecule separate and each functions as a template for synthesis of new complimentary strands
dispersive model
each strand of both daughter molecules contains a mixture of old and new synthesized DNA
conservative model
two parental strands reassociate after acting as templates for new strands
DNA Replication
origin of replication
replication of chromosomal DNA begins at a particular site
getting started
proteins recognize DNA sequences and separate the two strands and open a replication bubble
replication fork
at the end of each bubble, a Y-shaped region where parent strands of DNA are being unwound
helicases
enzymes that untwist the double helix at replication forks, separating two parent strands and becoming template strands
topoisomerase
enzyme that helps relieve this strain by breaking, and rejoining DNA strands
eukaryotic chromosomes have hundreds or thousands of replication origins
Synthesizing a New DNA Strand
primase
starts a complementary RNA chain with RNA nucleotide and adds RNA nucleotides using parent DNA strands as templates
primer
initial nucleotide chain produced during DNA synthesis is RNA
DNA polymerase
catalyze the synthesis of new DNA by adding nucleotides to the 3' end of a pre-existing chain
Antiparrallel Elongation
lagging strand
is synthesized discontinuously as a series of segments
leading strand
Only one primer is required for DNA pol III to synthesize the entire strand
Concept 16.3 Chromosome consists of DNA molecules packed with proteins
chromatin
complex of DNA and protein that fits into the nucleus through systems of packing
heterochromatin
interphase chromatin visible as irregular clumps with light microscope
euchromatin
disperse and less compact
Concept 16.1 DNA is genetic material
The Search for the Genetic Material
Evidence that DNA can transform bacteria
transformation
change in genotype or phenotype due to assimilation of eternal DNA by a cell
Evidence that viral DNA can program cells
virus
DNA enclosed by a protective protein
bacteriophages
DNA was shown to be genetic material for viruses to infect bacteria
Building a Structural Model of DNA
Each DNA nucleotide monomer consists of a nitrogenous base, a sugar deoxyribose and a phosphate group.
double helix
presence of two strands
antiparallel
subunits running in opposite directions