Genetics Flashcards
(171 cards)
1
Q
What are the 3 primary functions of genetic material?
A
- Coding for products
- Passing info between cells
- Passing info to the next generation
2
Q
What are two factors that determine what an organism is like?
A
- Gene sequence
2. The regulation of the expression of those genes
3
Q
What is the genome?
A
The complete sequence of nucleotides of the genetic material
4
Q
Is the genome usually DNA or RNA?
A
DNA, but RNA for certain viruses
5
Q
Greek: epi?
A
Around
6
Q
What are changes in the products and their amounts from the same gene code due to?
A
Different responses to the cellular environment
7
Q
What are epigenetics?
A
Changes that are made around the genome that do not alter the nucleotide sequence; they simply instruct the cellular machinery how to read the genome
8
Q
What are 3 examples of epigenetics?
A
- Attachment of chemical markers to the genome
- Histone protein modification
- Use of non-coding RNAs
9
Q
What kind of epigenetics can be passed on to the next generation?
A
- Attachment of chemical markers to the genome
2. Histone protein modification
10
Q
What is the MCAT definition of a gene?
A
Nucleotide sequence that can code for
- A certain product/set of products depending on factors like alternative splicing and protein modification
- A trait (genetically influenced characteristic
11
Q
What is the Central Dogma of gene expression?
A
DNA is transcribed to RNA, which is translated to amino acids to form a protein
12
Q
Who uses the Central Dogma of gene expression? Who does not?
A
All living organisms
Retroviruses
13
Q
How are double stranded DNA sequences arranged in eukaryotic cells?
A
Chromosomes
14
Q
What are histones? What kind of DNA is wrapped around them?
A
Globular proteins around which sections of DNA that are not in use are wrapped tightly
15
Q
What makes the DNA wrap around histones?
A
The net positive charge of histones attracts negatively charged DNA strands
16
Q
What is a nucleosome?
A
8 histones wrapped in DNA
17
Q
What are solenoids?
A
Wrapped nucleosomes
18
Q
What are supercoils?
A
Wrapped solenoids
19
Q
What is chromatin?
A
All the nucleosomes = The entire DNA/protein complex (w/ very small amount of RNA)
20
Q
How is the mass of chromatin divided?
A
1/3 DNA
2/3 protein
Small amount of RNA
21
Q
Where does chromatin get its name?
A
The large amount of basic amino acids in chromatin allow is to absorb basic dyes
22
Q
What about chromatin influences gene expression?
A
Its structure; how compact/coiled it is
23
Q
What is heterochromatin?
A
Chromatin that is tightly condensed
24
Q
What is constitutive heterochromatin?
A
Permanently coiled heterochromatin
25
What is eurochromatin?
Chromatin that is uncoiled and allows for transcription
26
When is eurochromatin coiled?
During nuclear division
27
What is single copy DNA? What does it do?
Nucleotide sequences represented by only one copy of a nucleotide sequence and are associated with regions of eurochromatin that are being actively transcribed
It codes for proteins
28
What is repetitive DNA? What does it do?
Multiple identical consecutive nucleotide sequences
| It does not code for proteins
29
Where is DNA found in animals?
In the nucleus and mitochondria
30
What is the most common example of epigenetic regulation through chemical change?
DNA methylation
31
What is DNA methylation?
Addition of an extra methyl group to particular cytosine nucleotides
32
What is the effect of DNA methylation?
Winds DNA more tightly
33
What is non-coding RNA (ncRNA)? What does it contribute to?
Sections of RNA that do not code for proteins and contribute to the regulation of chemical changes that affect chromatin structure
34
What is a somatic cell?
Any cell of a living organism other than the reproductive cells
35
How many DNA molecules in the nucleus of somatic cells?
46
36
What are homologues?
Two chromosomes that code for the same traits
37
How many homologous chromosomes do humans have?
23
38
What is a trait vs a version of the trait?
Eyes vs blue/brown...
39
What are alleles?
Different versions of the same gene
40
What are diploid cells?
Cells that contain homologous versions of chromosomes
41
What are haploid cells?
Cells that do not contain homologous versions of chromosomes
42
What is a methyl group?
R-CH3
43
Can genetic information code for non-protein products? Like?
Yes; RNA
44
Can you say that genetic differences between living organisms are negligible?
No; they are small but not negligible
45
When are chromosomes formed? From what?
During cellular division from chromatin that is more condensed
46
Does the number of chromosomes in a human cell double during replication?
No
47
What are chromatids?
The two strands of chromosomes joined together by a single centromere, formed from the duplication of the chromosomes during the early stages of cell division
48
What is G0?
The non-growing phase of a cell's life cycle
49
When does most protein production take place?
During G0
50
What are the 4 types of RNA
1. Ribosomal RNA (rRNA)
2. Transcription RNA (tRNA)
3. Messenger RNA (mRNA)
4. Small nuclear RNA (snRNA)
51
What does DNA become to produce proteins?
DNA --> mRNA --> proteins
52
What would happen if DNA was directly translated into amino acids?
Every cell in an organism would be the same
53
What are the 3 main stages of transcription?
1. Initiation
2. Elongation
3. Termination
54
What are transcription factors?
DNA binding proteins that identify the promoter on the DNA strand
55
What is a promoter on the DNA strand?
Sequence of DNA nucleotides that designate a beginning point for transcription
56
What happens during transcription initiation? 2 stages
1. Transcription factors bind to the DNA at a promoter and assemble into a transcription initiation complex which includes RNA polymerase
2. RNA polymerase unzips the DNA creating a transcription bubble
57
What is RNA polymerase?
The major transcription enzyme
58
What is the consensus sequence?
The most commonly found promoter by a given species of RNA polymerase
59
What does variation of the consensus sequence cause?
RNA polymerase will bind less tightly and less often to the promoter which means the genes will be transcribed less frequently
60
What happens during transcription elongation?
RNA polymerase transcribes only one strand of DNA into one complimentary RNA nucleotide sequence
61
What is the template strand?
The transcribed DNA strand
62
What is another name for the template strand?
Antisense strand
63
What is the coding strand? What does it do during transcription?
The strand of DNA that is not being transcribed by RNA polymerase; it protects its partner from degradation
64
What is another name for the coding strand?
Sense strand
65
In what direction does RNA polymerase move along the DNA strand?
3' --> 5'
66
In what direction is the RNA strand being built by RNA polymerase?
5' --> 3'
67
Are errors in transcription passed on to the next generation?
No
68
Are transcription errors harmful?
Usually not
69
Is there a proof-reading process for transcription?
No
70
What happens during termination?
RNA polymerase reaches the termination sequence
71
What proteins can termination involve? What is their role?
Rho proteins; they can help to dissociate the RNA polymerase from the DNA
72
What is nascent RNA?
The immediately formed RNA from transcription
73
When does regulation of genes occurs? By what?
During transcription by activators and repressors
74
How do activators and repressors work?
They bind to the DNA close to the promoter and either activate or repress the activity of RNA polymerase
75
How are activators/repressors usually regulated? By what?
By allosteric regulation by small molecules like cAMP
76
What are enhancers? How do they work?
Short non-coding regions of DNA in eukaryotes that act as activators but further away to the promoter
77
What is the primary function of gene regulation in prokaryotes?
To respond to changes in the environment
78
What is the primary function of gene regulation in eukaryotes?
To control the intra and extracellular environments of the cell
79
What is homeostatis?
Stable unchanging state of intra and extracellular environments
80
What is polycistronic mRNA?
mRNA that codes for multiple genes
81
What is monocistronic mRNA
mRNA that only codes for one gene?
82
Is prokaryotic mRNA polycistronic or monocistronic?
Polycistronic
83
Is eukaryotic mRNA polycistronic or monocistronic?
Monocistronic
84
What is the Jacob-Monod model?
It's a model of prokaryotic gene regulation in which the genetic unit/operon (operator + promoter + genes) contributes to a single mRNA
85
How is the amount of protein produced regulated?
By the amount of mRNA being produced
86
What happens to the mRNA shortly after it is transcribed?
It is degraded in the cytosol
87
What is a commonly used example of the Jacob-Monod model?
The lac operon in E. coli
88
What does the lac operon code for?
Enzymes that allow E. coli to import and metabolize lactose when there isn't enough glucose for fuel
89
What are the 2 conditions that activate the lac operon?
1. Glucose is scarce
| 2. Lactose is present
90
What happens when glucose is scarce in E. coli?
1. It creates high levels of cAMP
2. cAMP binds to and activates a catabolic activator protein (CAP)
3. The CAP binds to a CAP site next to the promoter of the lac operon
4. CAP activates the promoter
5. Formation of the transcription initiation complex
6. Production of 3 proteins
91
What is an operator?
A segment of DNA to which a transcription factor binds to regulate gene expression (usually near the promoter)
92
What is the role of the operator in the lac operon in E. coli?
When lactose isn't present, a lac repressor binds to the operator and prevents transcription of the lac genes
When lactose is present it binds to the repressor, which makes it unable to bind to the operator
93
What is the sequence of the different operon sites on the E. coli DNA?
Gene for repressor protein --> CAP site --> Promoter --> Operator
94
What happens after transcription?
Post-transcriptional modifications of the RNA
95
Do all types of RNA undergo post-transcriptional processing in prokaryotes?
No; tRNA and rRNa do but not mRNA
96
What is the purpose of post-transcriptional processing in general?
Further gene regulation
97
What is the primary transcript?
The initial mRNA sequence arrived at through transcription
98
What is the primary transcript also called?
pre-mRNA or heterogeneous nuclea RNA (hnRNA)
99
What are the 4 purposes of mRNA post-transcriptional processing in eukaryotes?
1. Helping the molecules that initiate translation to recognize the mRNA
2. Protecting the mRNA from degradation
3. Eliminating extraneous sequences of nucleotides
4. Providing a mechanism for variability in protein products
100
What are exonucleases?
Enzymes that cleave nucleotides
101
What is the 5' cap of the mRNA? What are its 2 functions?
The capped end of the mRNA
1. An attachment site in protein synthesis
2. Protection fro exonucleases
102
What does the 5' capping of mRNA use as energy?
GTP
103
What is the poly A tail of the mRNA?
The 3' end of the mRNA that is protected from exonucleases by the addition of a long series of adenine nucleotides
104
What is polyadenylation?
The addition of a long series of adenine nucleotides at the 3' end of mRNA
105
Whats is splicing of the mRNA? Where does it happen?
The excision of portions of the mRNA before it leaves the nucleus
106
What are introns?
The portions of the mRNA that are excised and discarded before the mRNA leaves the nucleus
107
What are exons?
The portions of the mRNA that will code proteins
108
Which are longer: exons or introns?
Introns
109
What happens after splicing of the mRNA?
The two ends of the chain are joined together
110
What do snRNPs contain? What is each of their role during splicing?
snRNPs (snurps) contain proteins and snRNA
1. snRNPs recognize nucleotide sequences at the end of introns and pull the ends of the introns together forming an intron loop
2. The snRNA acts as a ribozyme
111
What is a ribozyme?
An RNA molecule capable of catalyzing specific chemical reactions
112
What is the full name of snRNPs?
Small nuclear ribonucleoproteins
113
What is a lariat?
It is the intron loop formed by snRNPs during splicing of the mRNA
114
What is a spliceosome? What is its role?
The association of snRNPs and additional association proteins
It excises the introns and joins the ends of the exons together
115
What does alternative splicing allow the cell to do?
To incorporate different parts of the mRNA into the mature mRNA (likek omitting exons and incorporating introns)
116
What has recent research found about introns?
They play an important role in gene expression
117
What do sequences with abundant introns tend to correlate to?
Amplified protein production
118
What is the reason there are more proteins than genes?
Different splicing patterns of the same gene can create different proteins
119
How many proteins can the human genome code for?
About 100 K
120
How many protein-coding genes does the human genome have?
20 - 25 K
121
What does the difference in location between transcription and translation allow for?
Allows the RNA to be modified before it leaves the nucleus
122
Do prokaryotes have different locations for transcription and translation? What does this mean?
No; so they can happen at the same time and RNA is not modified before translation
123
Can alternative splicing cut exons?
Yes; sometimes only partial exons are included in the mRNA
124
What is a genetic code?
4 different mRNA nucleotides (A, C, G, U)
125
What is the triplet code?
Three nucleotides code for one amino acid
126
Why is the genetic code said to be degenerative?
Because with 4 possible nucleotides and triplet codes, there are 64 possible combinations, so more than one triplet code may code for the same amino acid
127
Why is the genetic code said to be unambiguous?
Because a given triplet code will only code for one amino acid
128
Is the genetic code universal?
Almost
129
What is the start codon?
AUG
130
What is a codon?
Three consecutive nucleotides on mRNA
131
What are the three possible stop codons?
1. UAA
2. UGA
3. UAG
132
What are two other names for stop codons?
Termination or nonsense codons
133
What is another name for the start codon?
Initiation codon
134
Which amino acid does the start codon code for?
Methionine
135
What is the role of tRNA during translation?
It renders the triplet code of the mRNA into a specific amino acid sequence
136
What are the two distinct ends of tRNA? What do they do?
1. One contains an anticodon (3 nucleotides) that binds to a complimentary codon sequence on mRNA
2. The other carries the amino acid that corresponds to that codon that can be added to the polypeptide chain as tRNAs bind to the codons along mRNA
137
What is wobble pairing?
The flexibility by which the tRNA anticodon can have one mismatched nucleotide (the third one) to the mRNA codon
138
What organelle does translation require?
A ribosome
139
Where is the ribosome found?
Free-floating in the cytosol or attached to the outer surface of the endoplasmic reticulum to form rough ER
140
What is a ribosome composed of? What is it made of?
Small subunit + large subunit made of rRNA and proteins
141
What is the ribosome and its subunits measured in terms of? In what unit?
Sedimentation coefficients in Svedberg units (S)
142
What is the sedimentation coefficient? What is it proportional to? What is it related to?
Speed of a particle in a centrifuge; proportional to mass; related to shape and density
143
Which are bigger: prokaryotic or eukaryotic ribosomes?
Eukaryotic ribosomes
144
Where are eukaryotic ribosomes manufactured?
In the nucleolus
145
After manufacture in the nucleolus, are the subunits of the ribosome transported together or separately into the cytosol?
Separately
146
Do sedimentation coefficients of ribosome subunits add up?
No
147
What are the 3 stages of translation?
The same ones as transcription
148
What happens during translation initiation? (3 stages)
1. Initiation factors (co-factor proteins) help the 5' end of mRNA to attach to the small subunit of the ribosome
2. A tRNA containing the 5'-CAU-3' anticodon settles on the P-site (with a methionine attached)
3. The large subunit of the ribosome joins to form the translation initiation complex
149
What does P site stand for? What happens at the P-site?
Peptidyl site
| The tRNA anticodon for methionine settles there
150
What is the translation initiation complex?
The mRNA, the tRNA, and the ribosome
151
When does most translation regulation occur?
During initiation
152
How does translation regulation occur?
By the recognition (or not) between the secondary structure of the mRNA and the ribosome
153
What happens during translation elongation?
1. A tRNA attaches to the A-site
2. The amino acid on the tRNA is joined to methionine by dehydration and bonding between the C-terminus of methionine and the N-terminus of the next amino acid
3. The tRNA with methionine slides to the E-site where it exits the ribosome
4. The tRNA with multiple amino acids slides to the P-site and frees the A-site for the next tRNA molecule
154
What does A-site stand for? What happens at the A-site?
Aminoacyl site
| The tRNA anticodon for all the amino acids of the polypeptide chain settle there
155
What is another way of saying carboxyl end of an amino acid?
C-terminus
156
What is another way of saying amine end of an amino acid?
N-terminus
157
What are the two enzymes at play during elongation?
1. Peptidyl transferase
| 2. rRNA
158
What happens during translation termination?
1. A stop codon reaches the A-site
2. Co-factor proteins known as release factors bind to the A-site
3. This allows for a water molecule to add to the end of the polypeptide chain
4. The polypeptide is freed from the tRNA and ribosome
5. The ribosome breaks into subunits`
159
Can ribosomes be recycled?
Yes
160
When does the polypeptide chain start folding?
During elongation
161
What is the role of chaperone proteins?
They help proteins fold during and after translation
162
What can happen to proteins at the end of translation?
Post-translational modifications
163
What is the purpose of post-translational modifications? How?
They regulate gene expression by affecting products become functional
164
What are 2 different examples of post-translational modifications?
1. Sugars, lipids, or phosphate groups can be added to amino acids
2. The polypeptide can be cleaved in different places
165
Where do proteins that were translated by free-floating ribosomes function?
In the cytosol
166
Where do proteins that were translated by rough ER ribosomes function?
In the ER lumen
167
What happens to proteins that were translated by rough ER ribosomes function? (2)
They become membrane bound proteins of the nuclear envelop, ER, Golgi, lysosomes, or plasma membrane
OR
They are secreted from the cell
168
Do free-floating ribosomes and rough ER ribosomes have the same structure?
Yes
169
What is the process by which proteins end up in different locations?
1. A signal peptide is recognized by a signal-recognition particle (SRP)
2. The SRP carries the free-floating ribosome complex to a SRP receptor protein at a specific location
3. The signal peptide is usually removed by an enzyme
170
What is a signal peptide?
A 20 amino acid sequence near the front of the polypeptide that is recognized by a SRP
171
Where is the ribosome when translation begins?
Free-floating
