Genetics Flashcards
(130 cards)
1
Q
What is the genetic code?
A
Set of rules by which information encoded with genetic material (DNA or RNA sequences) is translated into proteins (amino acid sequences) by living cells
2
Q
What is a codon?
A
Specific sequence of 3 nucleotides in mRNA that constitutes the genetic code for a particular amino acid
3
Q
What is a sense codon?
A
Codon that codes for an amino acid
4
Q
What is a nonsense codon?
A
Codon that causes the termination of translation
5
Q
What is the initiation codon? What does it code for?
A
The start codon
Methionine
6
Q
How many codons are there?
A
64
7
Q
How many sense codons are there?
A
61
8
Q
How many nonsense codons are there?
A
3
9
Q
What is translation?
A
Production of proteins
10
Q
What are the three stop codons?
A
UAA
UAG
UGA
11
Q
What is the start codon for most proteins and mRNA?
A
AUG
12
Q
What are the names of the three steps of translation?
A
Initiation
Elongation
Translocation
13
Q
What happens during the initiation step of translation?
A
Small subunit of ribosome binds to mRNA
tRNA binds to mRNA
Large subunit binds
Begins translation initiation complex
14
Q
What happens during the elongation step of translation?
A
More amino acids are added to the chain
Complementary tRNA arrives to A site
Large subunit provides enzymes, formidg bond between amino acids
Ribosome moves along mRNA strand
15
Q
What happens during the translocation step of translation?
A
tRNA moves from P site to E site (ready to leave ribosome)
A moves to P
A is ready to accept next tRNA
16
Q
How many times does translocation happen? When does it stop?
A
Over and over again
When it reaches the stop codon
17
Q
Where on the ribosome does elongation occur?
A
A site
18
Q
Where on the ribosome does translocation occur?
A
P & E Sites
19
Q
What are polyribosomes?
A
Multiple ribosomes arranged in short chains
20
Q
What is a termination factor?
A
Proteins that bind to the ribosome at the stop codon and help disassemble the ribosome
21
Q
In which kind of cell do transcription and translation occur at the same time?
A
Prokaryote
22
Q
Where does transcription occur in eukaryotes?
A
Nucleus
23
Q
What happens to RNA in eukaryotes before translation?
A
It has to be modified and protected before it enters the cytoplasm
24
Q
What is an operon?
A
Specific group or collection of regulated genes that have a special job
25
What is a repressible operon?
Operon that is always working, but can be turned off
26
What kind of operon is the lac operon?
Inducible operon
27
What does the lac operon do?
Breaks down lactose into monosaccharides (galactose & glucose)
28
What are the 3 features of the lac operon?
Regulator
Control locus
Structural locus
29
What are the 3 features of the lac operon?
Regulator
Control locus (regulatory part)
Structural locus
30
What is the promoter of the control locus recognized by?
RNA polymerase
31
What does the operator of the control locus of the lac operon do?
Sequence that acts as the on/off switch for transcription
32
What is the structural locus made up of?
Three genes, each coding for a different enzyme needed to catabolize lactose
33
What are the 3 enzymes that catabolize lactose?
Beta galactosidase
Lactose permease
Thiogalactoside transacetlyase
34
What are the 3 enzymes that catabolize lactose?
Beta galactosidase
Lactose permease
Thiogalactoside transacetlyase
35
What does beta galactosidase do?
Hydrolyzes lactose into monosaccharides
36
What does lactose permease do?
Transports lactose across cell membrane
37
What does thiogalactoside transacetlyase
Helps metabolism of lactose (non-essential function)
38
What are the three genes that code for the enzymes required for the catabolism of lactose?
lac z
lac y
lac a
39
What is the I gene responsible for?
Controls what happens to the other genes
Responsible for creating the represssor
40
What is the regulator composed of?
Gene that codes for protein
Capable of repressing the operon
41
What does the repressor do when lactose is not present?
Binds to the operator
Makes RNA polymerase unable to perform transcription
Translation is inhibited
Enzyme production is stopped
42
What happens to a lac operon cell when it encounters lactose?
Lactose turns on operon
Binds to repressor, making it inactive
Cell has different shape, cannot bind
RNA polymerase is free to transcribe
43
Lactose is an _______, which means it _______ the operon of the cell.
Inducer
Turns on
44
If lactose is present, the ________ binds to the ______ and changes its shape, so it cannot bind to the __________.
Inducer
Repressor
Operator
45
The lactose operon is regulated by the presence of what?
Glucose
46
What happens when there is a high amount of glucose in a cell?
Lactose operon is inhibited
47
What is CAP? What does it stand for?
A protein present in transcription
Catabolite Activator Protein
48
When glucose is present, cAMP levels are _________/
Low
49
When glucose is absent, cAMP levels are _________.
Very High
50
cAMP and CAP bind to form what?
cAMP-CAP Complex
51
What does the cAMP-CAP complex do?
Makes transcription really efficient
Max expression
52
What happens in the presence of glucose AND lactose?
cAMP levels are low and can't form complex with CAP
Transcription is not efficient, leading to low-level expression
53
What kind of operon is the arginine operon?
Repressible
| Anabolic
54
What is the arginine operon constantly making?
Amino acids
55
The arginine operon repressor is made by the ___________.
Regulatory gene
56
The arginine operon repressor is ________ and does not bind to the _______________.
Inactive
| Operator
57
Because the arginine operon repressor is inactive, ______________ attaches, and can perform transcription.
RNA polymerase
58
What is the result of transcription involving an arginine operon?
mRNA codes for enzymes that synthesize arginine
59
What is the major difference between anabolic and catabolic operons?
Anabolic - repressor binds and enables synthesis
Catabolic- repressor binds and inhibits synthesis
60
What is a mutation?
Permanent inheritable alteration in the DNA sequence or content of a cell
61
What is a spontaneous mutation?
DNA polymerase 3 makes a mistake during replication that is not repaired and leads to a change in the phenotype
62
What is an induced mutation?
Can be chemical or physical
63
What are the categories of mutations?
Silent
Missense
Nonsense
Back
64
What is a silent mutation?
Mutation produced but message was not affected
65
What is a missense mutation?
Change in the code so that a codon will be coding for another amino acid
66
What is a nonsense mutation?
Premature stop codon is introduced
67
What is a back-mutation?
Bacteria reverts back to the "wild type"
68
What is a frameshift mutation?
Very bad - deletion or insertion changes the message and how the protein is read
69
What are the two DNA repair mechanisms?
Specialized enzymes repair DNA
Excision repair
70
What enzyme is involved in specialized DNA repair?
Photolyase
71
What does DNA photolyase do?
Fixes the the pyramidine dimers
72
What is excision repair?
Incorrect or damaged bases are removed by first enzyme
Polymerase 1 and ligase fill in gaps
73
What is the Ames test used for?
To test if something has the potential to be a carcinogen or a mutagen
74
Explain the Ames test procedure.
1. Start with gram negative and histidine negative salmonella culture on two plates- test and control
2. Add potential mutagen to test plate
3. Look for appearance of colonies. Control plate will have back mutation (few colonies). Test plate will have many colonies if it's a carcinogen/mutagen
75
What is vertical genetic transfer?
When one cell divides into two
76
What is horizontal genetic transfer?
Transfer of cells to the same generation (cell to cell- NOT parent-daughter)
77
What are the three basic mechanisms of horizontal genetic transfer?
Transformation
Transduction
Conjugation
78
What does Griffith's transformation experiment prove?
DNA released from a killed cell can be acquired a live cell
79
What bacteria was involved in Griffith's transformation experiment?
Streptococcus pneumonia
Gram positive cocci, grows in pairs, two variations (smooth and rough)
80
What's the difference between the smooth and the rough Streptococcus pneumonia?
Smooth - produces capsule
Rough- no capsule
81
What happened when Griffith injected s-strain into the mouse?
Mouse got sick and died. :(
82
What happened when Griffith injected r-strain into the mouse?
Phagocytes eliminate disease. Mouse survives!
83
What happened when Griffith killed s-strain and injected it into the mouse?
Mouse survives.
84
What happened when Griffith combined live r-strain with dead s-strain and injected it into the mouse?
Mouse died :(
85
Why did the mouse die when injected with live r-strain with dead s-strain?
Cells that are competent (have membrane protein) can be transformed
Rough strain was transformed into the smooth strain
86
What is transformation?
DNA from dead cell is released into the environment and taken up into living cells
Some portion of the DNA may recombine into the genome of the recipient cell
87
What is conjugation?
Genetic transmission through direct contact between two cells
88
What is the difference between gram positive and gram negative conjugation?
Gram negative cells use a sex pilus
Gram positive cells use a cell bridge
89
What are the two common forms of conjugation found in bacteria?
F-factor transfer
HFR transfer
90
In what part of the cell does F-factor transfer occur?
Plasmids
91
What happens during F-factor transfer?
Cell sends one strand of the plasmid to the other cell
Once each cell has a strand, it's replicated, so each cell has a double strand
92
What are plasmids?
Double-stranded DNA that is smaller than and replicates independently of the cell chromosome
Can bear genes that code for adaptive traits
93
What is high frequency conjugation?
Transmission of chromosomal genes from a donor cell to a recipient cell
94
What is transduction?
Genetic transfer done by a virus
95
What are the two types of transduction?
Generalized
| Specialized
96
What happens during generalized transduction?
Virus attaches to a cell and injects genetic material
Starts making more viruses immediately
During synthesis, a piece of the bacteria's DNA gets incorporated into the virus
When those cells infect other bacteria cells, some cells get DNA from bacteria instead of the virus and obtain a new strain
97
What is specialized transduction?
Transfer of specific genetic material by means of a virus carrier
98
What bacterial lifecycle does specialized transduction occur during?
Lysogenic
99
What happens during specialized transduction?
Virus is incorporated into chromosome, and is specific to the DNA of the cell
Now has DNA from bacteria and virus
Recipient cells receive DNA
Either bacterial DNA or combination of viral and bacterial DNA can be incorporated into the chromosome
100
What is a transposon?
Pieces of DNA that can move in the chromosome
101
What are transposons also known as?
Jumping genes
102
Were transposons discovered in prokaryotes or eukaryotes?
Eukaryotes (corn)
103
What are transposons responsible for?
Can affect how genes are expressed
Cause mutations and antibiotic resistance
104
In bacteria, transposons move through ___________.
Plasmids
105
Which type of horizontal gene transfers are direct or indirect?
Conjugation is direct
| Transformation and transduction are indirect
106
What is the smallest unit of heredity?
a) chromosome
b) gene
c) codon
d) nucleotide
b) gene
107
The nitrogen bases in DNA are bonded to the:
a) phosphate
b) deoxyribose
c) ribose
d) hydrogen
b) deoxyribose
108
DNA replication is semi-conservative because the _______ strand will become half of the ________ molecule.
a) RNA, DNA
b) template, finished
c) sense, mRNA
d) codon, anticodon
b) template, finished
109
In DNA, adenine is the complementary base for __________ and cytosine is the complement for _____________.
a) guanine, thymine
b) uracil, guanine
c) thymine, guanine
d) thymine, uracil
c) thymine, guanine
110
tRNA is the molecule that:
a) contributes to the structure of ribosomes
b) adapts the genetic code to protein structure
c) transfers the DNA code to mRNA
d) provides the master code for amino acids
b) adapts the genetic code to protein structure
111
As a general rule, the template strand on DNA will always begin with:
a) TAC
b) AUG
c) ATG
d) UAG
a) TAC
112
The lac operon is usually in the _______ position, and is activated by a/an ___________ molecule.
a) on, repressor
b) off, inducer
c) on, inducer
d) off, repressor
b) off, inducer
113
Which genes can be transferred by all three methods of horizontal gene transfer?
a) capsule production
b) toxin production
c) F factor
d) drug resistance
d) drug resistance
114
Which of the following would occur through specialized transduction?
a) acquisition of HFr plasmid
b) transfer of genes for toxin production
c) transfer of genes for capsule formation
d) transfer of plasmid with genes for degrading pesticides
b) transfer of genes for toxin production
115
When genes are turned on differently under different environmental conditions, this represents a change in:
a) species
b) genotype
c) phenotype
d) growth rate
c) phenotype
116
True or false. The DNA pairs are held together primarily by covalent bonds.
False. The DNA pairs are held together primarily by hydrogen bonds.
117
True or false. Mutation usually has a negative outcome.
False. Although some mutations are harmful, many are neutral or helpful.
118
True or false. The lagging strand of DNA is replicated in short pieces because DNA polymerase can synthesize in only one direction.
True.
119
True or false. mRNA is formed by translation of a gene on the DNA template strand.
False. mRNA is formed by transcription of a gene on the DNA template strand.
120
True or false. A nucleotide is composed of a 5-carbon sugar, a phosphate group, and a nitrogenous base.
True.
121
True or false. Translation occurs in the nucleus of prokaryotes.
False.
122
True or false. Ribosomes in eukaryotes have three subunits.
False.
123
True or false. A missense mutation creates early stop codons in the mRNA.
False.
124
Genetic change in bacteria can be brought about by:
a) conjugation
b) transduction
c) mutation
d) all of the above
d) all of the above
125
According to the operon model for the synthesis of an inducible enzyme to occur, the:
a) end product must not be in excess
b) substrate must bind to the enzyme
c) substrate must bind to the repressor
d) repressor must bind to the operator
c) substrate must bind to the repressor
126
True or false. Transduction requires cell to cell contact.
False
127
The lac operon:
a) hydrolyzes lactose
b) produces constitutive enzymes
c) produces inducible enzymes
d) none of the above
c) produces inducible enzymes
128
The antibiotic streptomycin binds to the tRNA met at the 30S ribosome. From this information, you can conclude that streptomycin:
a) prevents transcription in eukaryotes
b) prevents transcription in prokaryotes
c) prevents translation in prokaryotes
d) prevents translation in eukaryotes
c) prevents translation in prokaryotes
129
An antibiotic that binds the 50S portion of the ribosome:
a) stops the ribosome from moving along the mRNA
b) prevents tRNA attachment
c) prevents transcription
d) none of the above
d) none of the above
130
True or false. Conjugation requires a bacteriophage.
False
