Unit 3.2 (ch17) bio

The information content of DNA is in the form of specific sequences of ___

nucleotides

Proteins are the links between ___ and ___

genotype, phenotype

____, the process by which DNA directs protein synthesis, includes two stages: ____ and ____

Gene Expression, transcription, translation

In 1909, British physician ____ first suggested that genes dictate phenotypes through enzymes that catalyze specific chemical reactions. He thought symptoms of an inherited disease reflect an inability to synthesize a certain enzyme. Alkaptonuria (black urine disease or alcaptonuria)

Archibald Garrod

____ and ____ exposed bread mold to X-rays, creating mutants that were unable to survive on minimal medium as a result of inability to synthesize certain molecules

Beadle, Tatum

They developed a one gene–one polypeptides hypothesis, which states

that each gene dictates production of a specific enzyme

___ is the intermediate between genes and the proteins for which they code

RNA

____ is the synthesis of RNA under the direction of DNA. produces messenger RNA (mRNA)

Transcription

___ is the synthesis of a polypeptide, which occurs under the direction of mRNA

Translation

____ are the sites of translation

Ribosomes

In ____, mRNA produced by transcription is immediately translated without more processing

prokaryotes

In a ____ cell, the ____ separates transcription from translation

eukaryotic, nuclear envelope

Eukaryotic RNA transcripts are modified through ____ to yield finished mRNA

RNA processing

The central dogma is the concept that cells are governed by a cellular chain of command:

DNA -> RNA -> protein

The flow of information from gene to protein is based on a____: a series of nonoverlapping, three-nucleotide words

triplet code

During ___, one of the two DNA strands called the ____ provides a template for ordering the sequence of nucleotides in an RNA transcript

transcription, template strand

During ____, the mRNA base triplets, called ____, are read in the 5’ to 3’ direction

translation, codons

Codons along an ____ molecule are read by translation machinery in the 5’ to 3’ direction

mRNA

____ is the DNA-directed synthesis of RNA

Transcription

RNA synthesis is catalyzed by ____, which pries the DNA strands apart and hooks together the RNA nucleotides

RNA polymerase

The DNA sequence where RNA polymerase attaches is called the ____ (both prokaryotes and eukaryotes)

only in bacteria, the sequence signaling the end of transcription is called the ___

promoter, terminator

The stretch of DNA that is transcribed is called a____

transcription unit

____ signal the initiation of RNA synthesis

Promoters

Transcription factors mediate the binding of ____ and the initiation of ____

RNA polymerase, transcription

The completed assembly of transcription factors and RNA polymerase II bound to a promoter is called a_____ (eukaryotes)

transcription initiation complex

A promoter called a ____ is crucial in forming the initiation complex in eukaryotes

TATA box

In bacteria, the polymerase stops transcription at the end of the ____

terminator

In eukaryotes, the polymerase continues transcription after the ____ is cleaved from the growing RNA chain; the polymerase eventually falls off the DNA

pre-mRNA

Enzymes in the *nucleus modify pre-mRNA before the genetic messages are dispatched to the ____

cytoplasm

Most eukaryotic genes and their RNA transcripts have long ____
stretches of ___ that lie between ___ regions

noncoding, nucleotides, coding

These noncoding regions are called intervening sequences, or ____

introns

The other regions from introns are called ____ because they are eventually expressed,
usually translated into amino acid sequences

exons

___ removes ___ and joins ___, creating an mRNA molecule
with a continuous coding sequence

RNA splicing, introns, exons

RNA splicing is carried out by ____. They consist of a variety of proteins and several small nuclear
_____ (snRNPs) that recognize the splice site

spliceosomes, ribonucleoproteins

____ are catalytic RNA molecules that function as enzymes and
can splice RNA (for prokaryotes)

Ribozymes

Three properties of RNA enable it to function as an enzyme

i. It can form a three-dimensional structure because of its ability to
base pair with itself
ii. Some bases in RNA contain functional groups
iii. RNA may hydrogen-bond with other nucleic acid molecules

Some genes can encode more than one kind of polypeptide,
depending on which segments are treated as exons during RNA
splicing. Such variations are called ______

alternative RNA splicing

Proteins often have a modular architecture consisting of discrete regions
called ____

domains

In many cases, different exons code for the different ____ in a protein

domains

A cell translates an mRNA message into protein with the help of____

transfer RNA (tRNA)

Flattened into one plane to reveal its base pairing, a tRNA molecule looks like a cloverleaf.

Because of _____, tRNA actually twists and folds into a three-dimensional
molecule L shaped

hydrogen bonds

Accurate translation requires two steps:

i. First: a correct match between a tRNA and an amino acid, done by the enzyme
aminoacyl-tRNA synthetase
ii. Second: a correct match between the tRNA anticodon and an mRNA codon

Flexible pairing at the third base of a codon is called ____ and allows some tRNAs to
bind to more than one codon

wobble

Ribosomes facilitate specific coupling of tRNA ____ with mRNA codons in protein
synthesis

anticodons

The two ribosomal subunits (large and small) are made of ____ and ____

proteins, ribosomal RNA

ribosome has three binding sites for tRNA:

i. The P site holds the tRNA that carries the growing polypeptide chain
ii. The A site holds the tRNA that carries the next amino acid to be added to the chain
iii. The E site is the exit site, where discharged tRNAs leave the ribosome

Building a polypeptide
a. The three stages of translation:

i. Initiation
ii. Elongation
iii. Termination

The initiation stage of translation brings together ___, a ____ with the first amino
acid, and the two ____ subunits.

mRNA, tRNA, ribosomal

First, a small ribosomal subunit binds with ___ and a special initiator tRNA

mRNA

Then the small ___ moves along the mRNA until it reaches the start ___

subunit, codon (AUG)

Proteins called ____ bring in the large subunit that completes the
translation initiation complex

initiation factors

During the elongation stage, ___ are added one by one to the preceding
amino acid
Each addition involves proteins called _____ and occurs in three steps:
1.___2.___3.___

amino acids, elongation factors, 

codon recognition, peptide bond formation, and translocation

Termination occurs when a ____ in the mRNA reaches the A site of the
____

stop codon, ribosome

The A site accepts a protein called a ____

release factor

The release factor causes the addition of a  ____ instead of an amino acid
This reaction releases the ____, and the translation assembly then comes
apart

water molecule, polypeptide

A number of ribosomes can translate a single mRNA simultaneously, forming a
____. They enable a cell to make many copies of a ____ very quickly

polyribosome,polypeptide

During and after synthesis, a polypeptide chain spontaneously coils and folds into its_____

ii. Proteins may also require ____ before doing their job

iii. Some polypeptides are activated by enzymes that ____ them

iv. Other polypeptides come together to form the subunits of a protein

three-dimensional shape

post-translational modifications

cleave

Two populations of ribosomes are evident in cells: ___ (in the cytosol) and ___ (attached to the ER)

ii. Free ribosomes mostly synthesize proteins that function in the ____

iii. Bound ribosomes make proteins of the ____ and proteins that are secreted from the cell

iv. Ribosomes are identical and can switch from____

v. Polypeptide synthesis always begins in the ____

vi. Synthesis finishes in the cytosol unless the polypeptide signals the ribosome to attach to the ER

vii. Polypeptides destined for the ER or for secretion are marked by a ____

viii. A _____ (SRP) binds to the signal peptide

ix. The SRP brings the signal peptide and its ribosome to the ER

free ribosomes, bound ribosomes, cytosol, endomembrane system, free to bound, cytosol, signal peptide, signal-recognition particle

____ can affect protein structure and Function

Point Mutations

____ are changes in the genetic material of a cell or virus

Mutations

____ are chemical changes in just one base pair of a gene

Point mutations

The change of a single nucleotide in a DNA template strand can lead to the production of an _____

abnormal protein

A _____ replaces one nucleotide and its partner with another pair of nucleotides

base-pair substitution

_____ still code for an amino acid, but not necessarily the right amino acid

____ change an amino acid codon into a stop codon, nearly always leading to a nonfunctional protein

Missense mutations, Nonsense mutations

Base-pair insertions or deletions

1. Insertions and deletions are additions or losses of nucleotide pairs in a gene

2. These mutations have a disastrous effect on the resulting protein more often than substitutions do

3. Insertion or deletion of nucleotides may alter the reading frame, producing a ____

frameshift mutation

____ mutations can occur during DNA replication, recombination, or repair 

____ are physical or chemical agents that can cause mutations

Spontaneous, mutagens