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Biology 1406 > Chapter 17 > Flashcards

Chapter 17 Flashcards

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AP® Biology flashcards Biology 101 flashcards
1
Q

The information of DNA is in the form of

A

specific sequences of nucleotides

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2
Q

The DNA inherited by an organism leads to

A

specific traits by dictating the synthesis of proteins

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3
Q

Proteins are the links between

A

genotype and phenotype

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4
Q

Gene expression, the process by which DNA directs protein synthesis, includes two stages:

A

transcription and translation

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5
Q

RNA is

A

the bridge between genes and the proteins for which they code

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6
Q

Transcription is

A

the synthesis of RNA using information in DNA.

Transcription happens in the nucleus of eukaryotes.

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7
Q

Transcription produces

A

messenger RNA (mRNA)

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8
Q

Translation is

A

the synthesis of a polypeptide, using information in the mRNA

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9
Q

Ribosomes are

A

the sites of translation

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10
Q

Every kind of cell has

A

ribosomes and DNA

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11
Q

In prokaryotes, translation of mRNA can begin before

A

transcription has finished

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12
Q

In a eukaryotic cell, the nuclear envelope

A

separates transcription from translation

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13
Q

Eukaryotic RNA transcripts are modified through

A

RNA processing to yield the finished mRNA

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14
Q

A primary transcript is the

A

initial RNA transcript from any gene prior to processing

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15
Q

The central dogma is the concept that

A

cells are governed by a cellular chain of command:

DNA—> RNA —> Protein

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16
Q

There are 20 amino acids, but

A

there are only four nucleotide bases in DNA

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17
Q

The flow of information from gene to protein is based on a

A

triplet code: a series of nonoverlapping, three-nucleotide words

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18
Q

The words of a gene are transcribed into

A

complementary nonoverlapping tree-nucleotide words of mRNA.

These words are then translated into a chain of amino acids, forming a polypeptide

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19
Q

During transcription,

A

one of the two DNA strands, called the template strand, provides a template for ordering the sequence of complementary nucleotides in an RNA transcript

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20
Q

The template strand is always the same strand for

A

a given gene

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21
Q

During translation,

A

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

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22
Q

Codons along an mRNA molecule are read by

A

translation machinery in the 5’ to 3’ direction

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23
Q

Each codon specifies the amino acid (one of 20) to be placed at the

A

corresponding position along a polypeptide

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24
Q

All 64 codons were deciphered by the

A

mid-1960s

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25
Q

Of the 64 triplets,

A

61 code for amino acids; 3 triplets are “stop signals to end translation (stop codons)

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26
Q

The genetic code is redundant (more than one codon may specify a particular amino acid) but

A

not ambiguous; no codon specifies more than one amino acid

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27
Q

Codons must be read in the correct reading frame (correct groupings) in order for

A

the specified polypeptide to be produced

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28
Q

AUG

A

start codon

always codes for placement of amino acid called methionine

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29
Q

The genetic code is

A

nearly universal, shared by the simplest bacteria to the most complex animals

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30
Q

Genes can be transcribed and translated after

A

being transplanted from one species to another

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31
Q

Transcription is the

A

DNA-directed synthesis of RNA

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32
Q

Transcription is the

A

first stage of gene expression

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33
Q

RNA synthesis is catalyzed by

A

RNA polymerase, which pries the DNA strands apart and hooks together the RNA nucleotides

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34
Q

The RNA is complementary to the

A

DNA template strand

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35
Q

RNA synthesis follows the same

A

base-pairing rules as DNA, except that uracil substitutes for thymine

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36
Q

The DNA sequence where RNA polymerase attaches is called the

A

promoter,

in bacteria, the sequence signaling the end of transcription is called the terminator

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37
Q

The stretch of DNA that is transcribed is called a

A

transcription unit

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38
Q

The three stages of transcription

A
  1. Initiation
  2. Elongation
  3. Termination
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39
Q

Promoters signal the transcriptional start point and usually

A

extend several dozen nucleotide pairs upstream of the start point

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40
Q

Transcription factors mediate the binding of

A

RNA polymerase and the initiation of transcription

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41
Q

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

A

transcription initiation complex

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42
Q

A promoter called a TATA box is

A

crucial in forming the initiation complex in eukaryotes

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43
Q

As RNA polymerase moves along the DNA,

A

it untwists the double helix, 10 to 20 bases at a time

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44
Q

Transcription progresses at a rate of

A

40 nucleotides per second in eukaryotes

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45
Q

A gene can be transcribed simultaneously by

A

several RNA polymerases

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46
Q

Nucleotides are added to the

A

3’ end of the growing RNA molecule

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47
Q

The mechanisms of termination are different in

A

bacteria and eukaryotes

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48
Q

In bacteria,

A

the polymerase stops transcription at the end of the terminator and the mRNA can be translated without further modification

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49
Q

In eukaryotes,

A

RNA polymerase II transcribes the polyadenylation signal sequence; the RNA transcript is released 10-35 nucleotides past this polyadenylation sequence

50
Q

Eukaryotic cells modify

A

RNA after transcription

51
Q

Enzymes in the eukaryotic nucleus modify

A

pre-mRNA (RNA processing) before the genetic messages are dispatched to the cytoplasm

52
Q

During RNA processing,

A

both ends of the primary transcript are usually altered.

Also, usually some interior parts of the molecule are cut out, and the other parts spliced together.

53
Q

Each end of a pre-mRNA molecule is modified in

A

a particular way

  • The 5’ end and receives a modified nucleotide 5’ cap
  • The 3’ end gets a poly-A tail
54
Q

These modifications to the end of a pre-MRNA molecule share several functions

A
  • They seem to facilitate the export of mRNA to the cytoplasm
  • They protect mRNA from hydrolytic enzymes
  • They help ribosomes attach to the 5’ end
55
Q

Most eukaryotic genes and their RNA transcripts have

A

long noncoding stretches of nucleotides that lie between coding regions

56
Q

These noncoding regions are called

A

intervening sequences, or introns

57
Q

The other regions are called

A

exons because they are eventually expressed, usually translated into amino acid sequences

58
Q

RNA splicing removes

A

introns and joins exons, creating an mRNA molecule with a continuous coding sequence

59
Q

In some cases,

A

RNA splicing is carried out by spliceosomes

60
Q

Spliceosomes consist of

A

a variety of proteins and several small nuclear rinonucleoproteins (snRNPs) that recognize the splice sites

61
Q

Ribozymes are

A

catalytic RNA molecules that function as enzymes and can splice RNA

62
Q

The discovery of ribozymes rendered

A

obsolete the belief that all biological catalysts are proteins

63
Q

There properties of RNA enable it to function as an enzyme:

A
  • it can form a three-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 hydrogen-bond with other nucleic acid molecules
64
Q

Some introns contain sequences that may regulate

A

gene expression

65
Q

Some genes can encode more than

A

one kind of polypeptide, depending on which segments are treated as exons during splicing.

This is called alternative RNA splicing

66
Q

Consequently, the number of different proteins an organism can produce is

A

much greater than its number of genes

67
Q

Proteins often have a modular architecture consisting of discrete regions called

A

domains

68
Q

In many cases,

A

different exons code for the different domains in a protein

69
Q

Exon shuffling may result in

A

the evolution of new proteins

70
Q

Translation is the

A

RNA-directed synthesis of a polypeptide

71
Q

Genetic information flows from

A

mRNA to protein through the process of translation

72
Q

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

A

transfer RNA (tRNA)

73
Q

tRNAs transfer

A

amino acids to the growing polypeptide in a ribosome

74
Q

Translation is a complex process in terms of its

A

biochemistry and mechanics

75
Q

Molecules of tRNA are not identical

A
  • Each carries a specific amino acid on one end

- each has an antiocodon on the other end; the anticodon base-pairs with a complementary codon on mRNA

76
Q

A tRNA molecule consists of

A

a single RNA strand that is only about 80 nucleotides long

77
Q

Flattened into one plane to reveal its base pairing,

A

a tRNA molecule looks like a cloverleaf

78
Q

Because of hydrogen bonds, tRNA actually

A

twists and folds into a three-dimensional molecule

79
Q

tRNA is roughly

A

L-shaped

80
Q

Accurate translation requires two steps

A
  • First: a correct match between a tRNA and an amino acid, done by the enzyme aminoacyl-tRNA synthetase
  • Second: a correct match between the tRNA anticodon and an mRNA codon
81
Q

Flexible pairing at the third base of a codon is called

A

wobble and allows some tRNAs to bind to more than one codon

82
Q

Ribosomes facilitate

A

specific coupling of tRNA anticodons with mRNA codons in protein synthesis

83
Q

The two ribosomal subunits (large and small) are

A

made of proteins and ribosomal RNA (rRNA)

84
Q

Bacterial and eukaryotic ribosomes are somewhat similar but have significant differences:

A

some antibiotic drugs specifically target bacterial ribosomes without harming eukaryotic ribosome

85
Q

A ribosome has three binding sites for tRNA:

A
  • the P site
  • the A site
  • the E site
86
Q

The P site

A

holds the tRNA that carries the growing polypeptide chain

87
Q

The A site

A

holds the tRNA that carries the next amino acid to be added to the chain

88
Q

The E site

A

is the exit site, where discharged tRNAs leave the ribosome

89
Q

The three stages of translation

A
  1. Initiation
  2. Elongation
  3. Termination

All three stages require protein “factors” that aid in the translation process

90
Q

The initiation stage of translation brings together

A

mRNA, a tRNA with the first amino acid, and the two ribosomal subunits

91
Q

First, a small ribosomal subunit binds with

A

mRNA and a special initiator tRNA

initiation stage in translation??

92
Q

Then the small subunit moves

A

along the mRNA until it reaches the start codon (AUG)

initiation stage in translation??

93
Q

Proteins called initiation factors bring in the

A

large subunit that completes the translation initiation complex

(initiation stage in translation)

94
Q

During the elongation stage,

A

amino acids are added one by one to the preceding amino acid at the C-terminus of the growing chain

95
Q

Each addition involves proteins called

A

elongation factors and occurs in three steps: codon recognition, peptide bond formation, and translocation

(elongation stage in translation)

96
Q

Translation proceeds along the

A

mRNA in a 5’ to 3’ direction

97
Q

Termination occurs when

A

a stop codon in the mRNA reaches the A site of the ribosome

termination stage in translation

98
Q

The A site accepts a protein called a

A

release factor

termination stage in translation

99
Q

The release factor causes the

A

addition of a water molecule instead of an amino acid.
This reaction releases the polypeptide, and the translation assembly then comes apart.

(termination stage in translation)

100
Q

A number of ribosomes can translate a single mRNA simultaneously forming a

A

polyribosome (or polysome)

101
Q

Polyribosomes enable a cell to

A

make many copies of a polypeptide very quickly

102
Q

Often translation is not sufficient to make a

A

functional protein

103
Q

Polypeptide chains are modified after translation or

A

targeted to specific sites in the cell

104
Q

During and after synthesis,

A

a polypeptide chain spontaneously coils and folds into its three-dimensional shape

105
Q

Proteins may also require

A

post-translational modifications before doing their job

106
Q

Some polypeptides are activated by

A

enzymes that cleave them

107
Q

Other polypeptides come together to form

A

the subunits of a protein

108
Q

Two populations of ribosomes are evident in cells:

A
  • free ribosomes (in the cytosol)

- bound ribosomes (attached to the ER)

109
Q

Free ribosomes mostly synthesize

A

proteins that function in the cytosol

110
Q

Bound ribosomes make proteins of the

A

endomembrane system and proteins that are secreted from the cell

111
Q

Ribosomes are identical and

A

can switch from free to bound

112
Q

Polypeptide synthesis always begins in

A

the cytosol

113
Q

Synthesis finished in the

A

cytosol unless the polypeptide signals the ribosome to attach to the ER

114
Q

Polypeptides destined for the ER for for secretion are marked by a

A

signal peptide

115
Q

A signal-recognition particle (SRP) binds to

A

the signal peptide

116
Q

The signal-recognition particle (SRP) brings teh

A

signal peptide and its ribosome to the ER

117
Q

Messenger RNA (mRNA) function

A

carries information specifying amino acid sequences of proteins from DNA to ribosomes

118
Q

Transfer RNA (tRNA) function

A

serves as adapter molecule in protein synthesis; translates mRNA codons into amino acids

119
Q

Ribosomal RNA (rRNA) function

A

plays catalytic (ribozyme) roles and structural roles in ribosomes

120
Q

Primar transcript function

A

serves as a precursor to mRNA, rRNA, or tRNA, before being processed by splicing or cleavage

121
Q

Small nuclear RNA (snRNA) function

A

plays structural and catalytic roles in spliceosomes

122
Q

SRP RNA function

A

is a component of the signal-recognition particle (SRP)

Biology 1406 (53 decks)

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