Chapter 17 Flashcards
Polysomes may be described as
Groups of ribosomes
The function of tRNA during protein synthesis is to
Deliver amino acids to their proper site during protein synthesis
How many nucleotides are needed to code for a protein with 450 amino acids?
At least 1,350
Because codons are nucleotide triplets, the number of nucleotides making up a generic message must be
Three times the number of amino acids in the protein product
Bacteria can transcribe and translate human genes to produce functional human proteins because
The genetic code is nearly universal
Stop codons are unique because they
Do not code for amino acids that allow a releasing factor to bind to the A site of the ribosome
Final stage of translation
Termination
Elongation (in translation) continues until
A stop codon in the mRNA reaches the A site of the ribosome
Release factor
Bonds directly to the stop codon in the A site
Causes the addition of a water molecule to the polypeptide chain
In order for transcription to occur in that strand, there would have to be a specific recognition sequence, called a __, to the left of the DNA sequence indicated
Promoter
Promoter
The DNA sequence where RNA polymerase attaches and initiates transcription
RNA polymerase binds
In a precise location and orientation on the promoter, determining where transcription starts and which of the two strands of the DNA helix is used as the template
Specific sequences of the nucleotides along the DNA mark
Where transcription begins
The TATA box is a __ that allows for the binding of __ and __
Eukaryotic promoter; transcription factors; RNA polymerase II
Transcription factors
Mediate the binding of RNA polymerase and the initiation of transcription
-after transcription factors are attached to the promoter, RNA polymerase II binds to it
Transcription initiation complex
The whole complex of transcription factors and RNA polymerase II bound to the promoter
RNA molecules that function as enzymes are called
Ribozymes
The “triplet code” refers to the fact that
Three nucleotides code for a single amino acid
__ is the synthesis of a polypeptide using information in the mRNA
Translation
Cell translates the nucleotide sequence of an mRNA molecule into the amino acid sequence of a polypeptide
Sites of translation
Ribosomes
Generic information of eukaryotic cells is transferred from the nucleus to the cytoplasm in the form of
RNA
Nuclear envelope separates
Transcription from translation in space and time
Transcription occurs
In the nucleus
And then mRNA is then transported to cytoplasm, where translation occurs
An exception to the one gene-one enzyme hypothesis is
Not all genes code for enzymes; some genes code for structural proteins such as keratin
What is the proper order in the expression of a eukaryotic gene?
Transcription
RNA processing
Translation
Modification of protein
DNA ->
RNA -> PROTEIN
Genes program
Protein synthesis via genetic messages in the form of mRNA
The bonds that hold tRNA molecules in the correct three-dimensional shape are
Hydrogen bonds
Because the bacterial cell’s DNA is not surrounded by a nuclear envelope
Coupled transcription and translation occurs
The type of point mutation that results in a premature stop codon is called a
Nonsense mutation
Gene expression is
The process by which DNA directs the synthesis of proteins
Eukaryotic processing of the primary transcript includes
The addition of a 5’ cap, a 3’ Poly-A tail, and the splicing out of introns
What is an example of a post-translational modification of a polypeptide?
Cleavage of a polypeptide into two or more chains
Nonsense mutations can
Also change a codon for an amino acid into a stop codon
Causes translation to be terminated early
Resulting polypeptide will be shorter than regular
Lead to nonfunctional proteins
In eukaryotic cells, a __ by a __ targets a growing peptide to the ER
Signal peptide
Signal-recognition particle
What best describes the arrangement of generic information in a DNA molecule?
The three-nucleotide words of a gene are arranged in a non overlapping series on the DNA template strand
Transcription is
The synthesis of RNA using information in the DNA
Insertions and deletions are called
Frameshift mutations
What is a key difference in gene expression between eukaryotic and prokaryotic cells?
In prokaryotic cells, the mRNA transcript is immediately available as mRNA without processing
Who made the one gene-one enzyme hypothesis?
Beadle and Tatum
What catalyzes the linkage between ribonucleotides to form RNA during gene expression?
RNA polymerase
Gene expression
Process by which DNA directs synthesis of proteins
One gene-one enzyme hypothesis
Function of a gene is to dictate the production of a specific enzyme
Genes provide
Instructions for making specific proteins, but do not directly build proteins
RNA has
Uracil instead of T
Single stranded
DNA protein requires
Transcription and translation
Transcription
Synthesis of RNA using information in the DNA
Two nucleic acids (DNA&RNA) are written in different forms of the same language. Information is transcribed, rewritten, from DNA to RNA
DNA strand can
Serve as a template for assembling a complementary sequence of RNA nucleotides
Messenger RNA (mRNA)
Transcript of the gene’s protein building instructions
Carries a generic message from the DNA to the protein synthesizing machinery of the cell
Transcription is
The general term for synthesis of any kind of RNA on a DNA template
Translation
Synthesis of a polypeptide using the information in the mRNA
During this, the cell translates
The nucleotide sequence of an mRNA molecule into an amino acid sequence of a polypeptide
Ribosomes are
The sites of translation, molecular complexes that facilitate the orderly linking of amino acids into polypeptide chains
Bacteria cell
Allows translation of mRNA to begin while is transcription is still in progress
Eukaryotic cell
Nuclear envelope separates transcription from translation in space and time
Transcription occurs
In nucleus before RNA transcripts can leave the nucleus, they’re modified to produce mRNA
mRNA then transported to the cytoplasm
Primary transcript
Initial RNA transcript from any gene
Genes program
Protein synthesis via genetic messages in the form of messenger RNA
DNA RNA protein
Triplet code
Generic instructions for a polypeptide chain are written in the DNA as a series of nonoverlapping, 3 nucleotide words
Transcribed into complementary series of nonoverlapping, 3 nucleotide words in mRNA, then into a chain of amino acids
Template strand
For each gene, only one of 2 DNA strands is transcribed, provides the pattern (template) for the sequence of nucleotides in an RNA transcript
During transcription, the gene determines the
Sequence of nucleotide bases along the length of the RNA molecule that is being synthesized
Codons
RNA nucleotide triplets, written in 5-3 direction
An mRNA molecule is complementary rather than identical to its DNA template because
RNA nucleotides are assembled on the template according to base pairing rules
The term codon is also used for
The DNA triplets along the nontemplate strand
Reading frame
Correct groupings
mRNA, carrier of information from DNA to the cell’s protein synthesizing machinery
Transcribed from the template strand of a gene
RNA polymerase pries
The two strands of DNA part and joins together RNA nucleotides complementary to the DNA template strand, elongating the RNA polynucleotide
Assembles a polynucleotide only in its 5-3 direction
Can start a chain and initiates transcription
Bacteria, the sequence that signals the end of transcription is called
Terminator
Transcription unit
Stretch of DNA to un stream from the promoter that it transcribed into an RNA molecule
Start point
The nucleotide where RNA synthesis actually begins
Promoter of a gene includes within it in the transcription and extends several dozen or more nucleotide pairs upstream from the start point
Eukaryotic transcription factors
Mediate the binding of RNA polymerase and the initiation of transcription
Transcription initiation complex
Whole complex of transcription factors and RNA polymerase Is bound to the promoter
TATA box
Shows the role of transcription factors and a crucial promoter DNA sequence
RNA polymerase moves along the DNA
Untwists the double helix
Enzyme adds nucleotides to the 3 end of the growing RNA molecule as it continues along the double helix
Bacteria transcription proceeds through
A terminator sequence in the DNA
RNA processing
Both ends of the primary transcript are altered
Poly A tail
At 3 end, enzyme adds 59-250 more nucleotides
RNA splicing
Removal of large portions of the RNA molecule that is initially synthesized
Introns
Noncoding segments of nucleic acids that lie between coding regions
Exons
Other regions, they are eventually expressed, usually by being translated into amino acid sequences
Spliceosome
Small RNAs and proteins, large complex
Binds to several short nucleotide sequences along an intron, including key sequences at each end
Intron released and spliceosome joins together 2 exons
Ribozymes
RNA molecules that function as enzymes
Alternative RNA splicing
Genes can give rise to 2 or more different polypeptides, depending on when segments are treated as exons
Domains
Proteins often have a molecular architecture consisting of discrete structural and functional regions
Exon shuffling
The presence of introns in a gene may facilitate the evolution of a new and potentially beneficial proteins
Transfer RNA
The translator, series of codons along an mRNA molecule
Functions to transfer amino acids from the cytoplasmic pool of amino acids to a growing polypeptide in a ribosome
Each tRNA molecule translates a given mRNA coding into a certain amino acid
Anticodon
Nucleotide triplet that basa pairs to a specific mRNA codon
tRNA molecules are transcribed from
DNA templates
Aminoacyl-tRNA synthetases
Correct matching up of tRNA and amino acid is carried
Wobble
Flexible base pairing at this codon position
Ribosomal RNAs (rRNA)
A ribosome that consists of a large subunit, each made up of proteins and one or more
Most abundant type
P site (Peptidyl-tRNA binding site)
Holds the tRNA carrying the growing polypeptide chain, while the A site (aminoacyl-tRNA binding site) holds the tRNA carrying the next amino acid to be added to the chain
Discharged tRNAs leave the ribosome from the
E site
Signal peptide
Targets the protein to the ER
the polypeptides of proteins destined for the endomembrane sytem or for secretion are marked by
Signal recognition particle
Protein RNA complex
Polyribosomes (polysomes)
Strings of ribosomes
Enable a cell to make many copies of a polypeptide very quickly
Mutations
Changes to genetic information, responsible for diversity
Point mutation
Chanda in a single nucleotide pair of a gene
Small-scale mutations
Single nucleotide pair substitutions
Nucleotide pair insertions or deletions
Can involve 1 or 2 pairs
Nucleotide pair substitution
Replacement of one nucleotide and its partner with another pair of nucleotides
Silent mutation
Change in nucleotide pair that may transform one codon into another that is translated into the same amino acid
Has no observant effect on the phenotype
Can occur outside genes as well
Missense mutations
Substitutions that change one amino acid to another
Little effect on the protein
Nonsense mutations
Point mutation that can also change a codon for an amino acid into a stop codon
Causes translation to end prematurely
Resulting polypeptide will be shorter than the polypeptide encoded by the normal gene
Lead to nonfunctional proteins
Insertions and deletions are
Additions or losses of nucleotide pairs in a gene
Often have a disastrous effect on resulting protein more often than substitutions do
Alter the reading frame of the generic message, the triplet grouping of nucleotides on the mRNA that’s read during translation
Frameshift mutation
Frameshift mutation
Occurs whenever the number of nucleotides inserted or deleted is not a multiple of 3
Protein almost certain to be nonfunctional, unless frameshift very near end of gene
Mutagens
Physical and chemical agents that cause mutations
A gene is a region of DNA that can be expressed to
Produce a final functional product that is either a polypeptide or an RNA molecule
Transcription into RNA then
Translation into a polypeptide that forms a protein or specific structure and function
Ribozymes are
Catalytic RNA molecules that function as enzymes
3 properties of RNA that enable it to function as an enzyme
Can form 3 dimensional structure because of its ability to base pair with itself
Some bases in RNA contain functional groups that may participate in catalysis
RNA may H-bond with their nucleic acid molecules
Some introns contain sequences that
May regulate gene expression
Alternative RNA splicing
Some genes can encode more than one kind of polypeptide, depending on which segments are treated as exons during splicing
Domains
Discrete regions
Proteins often have a modular architecture consisting of discrete regions
Different exons code for
Different proteins
Translation is
mRNA to protein
tRNA helps
Cell translate an mRNA message into protein
Transfers amino acids
Carries anticodon
Accurate translation
Correct match between tRNA and an amino acid, done by the enzyme aninoacyl tRNA synthetase
Correct match between the tRNA anticodon and mRNA codon
Gene determines
Primary structure, and primary structure determines shape
Bacteria transcription/translation
Can happen at the same time
In eukaryotic cells, the nuclear envelope separates
Transcription/translation
Point mutations
Chemical changes in just one base pair of a gene
Change of single nucleotide in a DNA template strand can lead to production of abnormal protein
Once mutation occurs, usually stays
Nucleotide pair replaces
One nucleotide and its partner with another pair of nucleotides
Missense mutation
Still codes for an amino acid, but not the correct amino acid
Silent mutation
No effect on the amino acid produced by a codon because of the redundancy of the genetic code
Nonsense mutation
Change an amino acid codon into a stop codon, nearly always leading to a nonfunctional protein
Insertion/deletion
May alter the reading frame-frameshift mutation
Disastrous effect on the resulting protein more often than substitutions do
Additions or losses of nucleotide pairs in a gene
Possibility of amino acid changes
Maybe changes the secondary and tertiary, definitely changes the primary
Spontaneous mutations can occur during DNA replication, recombination, or repair
.
Gene is
A discrete unit of inheritance, region of DNA that can be expressed to produce a final functional product that is either a polypeptide or an RNA molecule
Coding segments are
Exons
