chapter 17: DNA test 5 Flashcards
The information content of genes is in the specific sequences of ___
The DNA inherited by an organism leads to
specific traits by dictating the ___
Proteins are the links between ___ and ___
Gene expression, the process by which DNA directs protein synthesis, includes two stages: ___ and ___
nucleotides
synthesis of proteins
genotype and phenotype
transcription and translation
(The Study of Metabolic Defects Provided Evidence that Genes specify Proteins)
In 1902, British physician Archibald Garrod first suggested that genes dictate ___ through enzymes that catalyze specific chemical reactions
He thought symptoms of an inherited disease reflected an inability to ___
This led to one ___ hypothesis (remember…. enzymes are proteins)
___ is current hypothesis
phenotypes
synthesize a certain enzyme
gene-one enzyme
One gene-one polypeptide
(Transcription and Translation link gene to protein (polypeptide)
RNA is the ___ between genes and the proteins for which they code
___ is the synthesis of RNA using information in DNA
Transcription produces ___
___ is the synthesis of a polypeptide (protein), using information in the mRNA
___ are the sites of translation
bridge (intermediate)
Transcription
messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA)
Translation
Ribosomes (rRNA)
A ___ is the initial RNA transcript from any gene prior to processing
The ___ is the concept that cells are governed by a cellular chain of command:
DNA → RNA → protein
primary transcript
central dogma
(Codons: Triplets of Nucleotides)
The flow of information from gene to protein is based on a ___: a series of nonoverlapping, three-nucleotide words
These triplets are the smallest units of uniform length that can code for an ___.
triplet code
amino acid
During transcription, one of the two DNA strands, called the ___, provides a template for ordering the sequence of complementary nucleotides in an RNA transcript
(The template strand is always the same strand
for a given gene)
The complementary RNA molecule is synthesized according to base-pairing rules except ___ is the complementary base to adenine (instead of thymine)
template strand
uracil (U > A instead of U > T)
During translation, the mRNA base triplets, called ___, are written in the ___ direction
Each codon specifies the ___ (one of 20)
to be placed at the corresponding position along
a polypeptide
codons
5′ → 3′
amino acid
Of the 64 codons, 61 code for ___; 3 codons are ___ signals to end translation
There is ___ in the genetic code (more than one codon may specify a particular amino acid) but no ___ (no codon specifies more than one amino acid)
The correct starting point is necessary to extract the message. This establishes the ___ (correct groupings) in order for the specified polypeptide to be produced
amino acids
“stop”
redundancy
ambiguity
reading frame
The genetic code is nearly ___, shared by the simplest bacteria to the most complex animals
Genes can be ___ and ___ after being transplanted from one species to another
universal
transcribed and translated
(Transcription is the DNA-directed synthesis of RNA: A closer look)
Transcription is the ___ stage of gene expression
The RNA synthesized is complementary to the ___ template strand
first
DNA
(Molecular Components of Transcription)
RNA synthesis is catalyzed by ___, which separates the DNA strands apart and joins together the ___
Like DNA polymerase RNA polymerase assembles nucleotides in the 5’- 3’ direction.
Unlike DNA polymerases, RNA polymerases are able to start a chain from scratch, they do not need a ___.
RNA polymerase
RNA nucleotides
primer
The DNA sequence where RNA polymerase attaches is called the ___.
The stretch of DNA that is transcribed is called a ___
promoter
transcription unit
Synthesis of an RNA Transcript
The three stages of transcription
Initiation
Elongation
Termination
(RNA Polymerase Binding and Initiation of Transcription)
Promoters signal the transcriptional ___
In eukaryotes, ___ mediate the binding of RNA polymerase and the initiation of transcription
The completed assembly of transcription factors and RNA polymerase bound to a promoter is called a ___
A promoter called a ___ is crucial in forming the initiation complex in eukaryotes
start point
transcription factors
transcription initiation complex
TATA box
(Elongation of the RNA Strand)
As RNA polymerase moves along the DNA, it ___ the double helix, 10 to 20 bases at a time
Transcription progresses at a rate of ___ in eukaryotes
A gene can be transcribed simultaneously by several RNA polymerases
Nucleotides are added to the ___ of the
growing RNA molecule
untwists
40 nucleotides per second
3′ end
(Eukaryotic cells modify RNA after transcription)
Enzymes in the eukaryotic nucleus modify ___ (RNA processing) before the genetic messages are dispatched to the ___
During RNA processing, both ends (5’ and 3’) of the primary transcript are usually ___
pre-mRNA
cytoplasm
altered
(Alteration of mRNA Ends)
Each end of a pre-mRNA molecule is modified in a particular way
The 5′ end receives a modified nucleotide 5′ ___
The 3′ end gets a ___
cap
poly-A tail
(RNA Splicing)
Most eukaryotic genes and their RNA transcripts have long noncoding stretches of nucleotides that lie between coding regions
These noncoding regions are called intervening sequences, or ___
The other regions are called ___ because they are eventually expressed, usually translated into amino acid sequences
___ removes introns and joins exons, creating an mRNA molecule with a continuous coding sequence
introns
exons
RNA splicing
(Genetic information flows from mRNA to protein through the process of translation)
A cell translates an mRNA message into protein by interpreting a series of codons along an mRNA molecule to build a ___
Transfer RNA (tRNA) transfers the ___ to ___ in a ribosome
Translation is a complex process in terms of its biochemistry and mechanics
polypeptide
amino acids to the growing polypeptide
(The Structure and Function of Transfer RNA)
Molecules of tRNA are not identical
- Each carries a specific ___ on one end
- Each has an ___ on the other end; the anticodon base-pairs with a complementary codon on mRNA
The anticodon pairs with a complementary codon on the mRNA
Codon by codon, the tRNAs deposit the amino acids in the prescribed order, and the ribosome joins the amino acid into a polypeptide
amino acid
anticodon
(The Structure and Function of Transfer RNA)
A tRNA molecule consists of a single RNA strand that is only about ___ nucleotides long
Flattened into one plane to reveal its base pairing, a tRNA molecule looks like a ___
Like mRNA, tRNA molecules are transcribed from ___
80
cloverleaf
DNA
Accurate translation requires two steps
First: a correct match between a tRNA and an amino acid, done by the enzyme ___
Second: a correct match between the tRNA anticodon and an ___
Flexible pairing at the third base of a codon is called ___ and allows some tRNAs to bind to more than one codon
aminoacyl-tRNA synthetase
mRNA codon
wobble
(Ribosomes)
Ribosomes facilitate specific coupling of ___ with mRNA codons in protein synthesis
The two ribosomal subunits (large and small) are made of proteins and ___
tRNA anticodons
ribosomal RNA (rRNA)
A ribosome has three binding sites for tRNA
The ___ site holds the tRNA that carries the growing polypeptide chain
The ___ site holds the tRNA that carries the next amino acid to be added to the chain
The ___ site is the exit site, where discharged tRNAs leave the ribosome
P
A
E
(Building a Polaypeptide)
The three stages of translation
1.
2.
3.
All three stages require protein “factors” that aid in the translation process
Energy is required for some steps also
Initiation
Elongation
Termination
(Ribosome Association and Initiation of Translation)
___ brings together mRNA, a tRNA with the first amino acid, and the two ribosomal subunits
Initiation
(Elongation of the Polypeptide Chain)
During ___, amino acids are added one
by one to the growing chain
Each addition involves proteins called elongation factors and occurs in three steps: ___, ___, and ___
Translation proceeds along the mRNA in a
5′ → 3′ direction
elongation
codon recognition, peptide bond formation, and translocation
(Termination of Translation)
Termination occurs when a ___ in the mRNA reaches the A site of the ribosome
The A site accepts a protein called a ___
This reaction releases the polypeptide, and the translation assembly comes apart
stop codon
release factor
(Targeting Polypeptides to Specific Locations)
Two populations of ribosomes are evident in cells: ___ (in the cytosol) and ___ (attached to the ER)
Free ribosomes synthesize proteins that function in the ___
Bound ribosomes make proteins of the ___ and proteins that are secreted from the cell
Ribosomes are identical and can switch from free to bound
free ribosomes, bound ribosomes
cytosol
endomembrane system
Polypeptide synthesis always begins in the ___
Synthesis finishes in the cytosol unless the polypeptide signals the ribosome to attach to
the ER
Polypeptides destined for the ER or for secretion are marked by a ____
cytosol
signal peptide
(Concept 17.5: Mutations of one or a few nucleotides can affect protein structure and function)
___ are changes in the genetic material of a cell
___ are chemical changes in just one base pair of a gene
The change of a single nucleotide in a DNA template strand can lead to the production of an abnormal protein
Mutations
Point mutations
Substitutions
___ have no effect on the amino acid produced by a codon because of redundancy in the genetic code
___ still code for an amino acid, but not the correct amino acid
___ change an amino acid codon into a stop codon, nearly always leading to a nonfunctional protein
Silent mutations
Missense mutations
Nonsense mutations
(Insertions and Deletions)
Insertions and deletions are additions or losses of ___ in a gene
These mutations have a disastrous effect on the resulting protein more often than substitutions do
Insertion or deletion of nucleotides may alter the reading frame, producing a ___
nucleotide pairs
frameshift mutation
(New Mutations and Mutagens)
Spontaneous mutations can occur during DNA replication, recombination, or repair
___ are physical or chemical agents that can cause mutations
Mutagens
(What Is a Gene? Revisiting the Question)
The idea of the gene has evolved through the history of genetics
We have considered a gene as
A discrete unit of inheritance
A region of specific nucleotide sequence in
a chromosome
A DNA sequence that codes for a specific polypeptide chain
