Exam 3 Flashcards
1
Q
What is the cell theory?
A
All life forms are made from one or more cells. The cell is the smallest form of life. Cells only arise from pre-existing cells.
2
Q
What is a cell?
A
A highly organized compartment that is bound by a plasma membrane and contains concentrated chemicals in an aqueous solution.
3
Q
Mitosis produces genetically _________ cells. What are these cells called?
A
identical, somatic cells
4
Q
Meiosis produces genetically _________ cells. What are these cells called?
A
different, gametes
5
Q
What is mitosis responsible for?
A
An organism’s growth
6
Q
What leads to cancer?
A
An excessive amount of cell division by mitosis
7
Q
What is a chromosome?
A
Long DNA molecules that wrap around proteins.
8
Q
What are the proteins found in chromosomes called?
A
Histones
9
Q
What is a gene?
A
A section of DNA that encodes a specific RNA and/or protein
10
Q
Each chromosome occupies a ______ area within the nucleus.
A
distinct
11
Q
What happens before mitosis?
A
Each chromosome is replicated
12
Q
What are chromosomes made of after replication?
A
Two sister chromatids, a centromere, and a kinetochore
13
Q
What is the centromere?
A
The point where two sister chromatids are joined
14
Q
What is a kinetochore?
A
A complex of proteins associated with the centromere
15
Q
Sister chromatids are 100% _______.
A
identical
16
Q
What occurs after replication?
A
Chromosomes condense from long, thin filaments into compact structures that can be moved around the cell.
17
Q
How does chromosome condensation occur?
A
With the help of many proteins
18
Q
What does chromosome condensation aid in during mitosis and meiosis?
A
Segregation of chromosomes
19
Q
What are the two phases of the cell cycle?
A
The M phase and interphase
20
Q
What is the M phase?
A
A dividing phase called the mitotic phase or the meiotic phase. This includes cytokinesis.
21
Q
What is G1 in the cell cycle?
A
Cell growth (first gap)
22
Q
What is S in the cell cycle?
A
DNA synthesis (DNA replication)
23
Q
What is G2 in the cell cycle?
A
Cell growth (second gap)
24
Q
What are the three types of cytoskeletal elements?
A
Microtubules, actin filaments (microfilaments), and intermediate filaments
25
What are actin filaments and microtubules made of?
protein monomers
26
What is an actin filament?
A two-stranded helical polymer made of the protein actin
27
What is a microtubule?
A hollow cylinder made from the protein tubulin
28
What is the inside of a microtubule called?
The lumen
29
What is the diameter of a microtubule?
25 nm
30
What are actin filaments and microtubules capable of doing?
They can assemble and disassemble
31
Actin filaments and microtubules are __________.
asymmetrical
32
What causes the polarity of actin filaments and microtubules?
The shape of their monomers
33
Which end of actin filaments and microtubules allows for the fast addition of monomers?
The plus end
34
Which end of actin filaments and microtubules allows for a slow addition of monomers?
The minus end
35
What are motor proteins?
Proteins that allow for movement along the cytoskeleton
36
Motor proteins require ___.
ATP
37
Which motor protein moves along microtubules?
kinesin
38
True or false: A motor protein can move in both directions.
False. Motor proteins can only move in one direction.
39
Kinesin ____ along a microtubule track.
walks
40
Which structure of kinesin is the transport vesicle?
The tail
41
Which structure of kinesin actually touches the microtubule?
The head
42
What are the five sub-phases of mitosis?
1. Prophase
2. Prometaphase
3. Metaphase
4. Anaphase
5. Telophase
43
What happens during prophase of mitosis?
Chromosomes condense, and the spindle apparatus begins to form.
44
What is the spindle apparatus?
A network of microtubules
45
What happens during prometaphase of mitosis?
The nuclear envelope breaks down, microtubules contact kinetochores.
46
What happens during metaphase of mitosis?
Chromosomes complete migration to the middle of the cell
47
What is the microtubule organizing center (MTOC) made of?
A centrosome (2 centrioles)
48
True or false: Microtubules grow only in the direction of the chromosomes.
False. Microtubules grow outward from the centrosome, radiating throughout the cell.
49
What are astral microtubules?
Microtubules that do not grow towards the middle of the cell.
50
What are kinetochore microtubules?
Microtubules that make contact with a kinetochore
51
What are overlap microtubules?
Microtubules that grow in the direction of the middle of the cell, but they do not make contact with a kinetochore. Instead, they overlap each other.
52
How do chromosomes move during prometaphase?
Motor proteins walk chromosomes to the plus end of microtubules.
53
What happens during anaphase of mitosis?
Sister chromatids separate into daughter chromosomes and are pulled apart.Protein cohesion of centromeres is degraded
54
How do chromosomes move during anaphase?
A ring attached to kinetochore fibers and kinetochore plates move towards the minus end of the microtubule, breaking the microtubule into tubulin subunits.
55
What happens during telophase of mitosis?
The nuclear envelope reforms, and chromosomes de-condense.
56
What happens during cytokineis?
An actin-myosin ring causes the plasma membrane to begin to pinch in and two daughter cells form.
57
What is myosin?
A motor protein
58
What is the cleavage furrow?
The indentation of the cell's surface
59
How does cytokinesis occur in plants?
Microtubules direct vesicles from the Golgi apparatus to the center of the cell where they fuse and form a cell plate.
60
How do chromosomes come in diploid organisms?
In pairs
61
What are homologous chromosomes?
Chromosomes that have the same shape and size
62
What is the karyotype of an organism?
The number and type of chromosomes present
63
How many chromosomes do humans have? How many pairs?
46 chromosomes, 23 pairs of chromosomes
64
In a specific position, homologous chromosomes carry __________ genes.
homologous
65
What are different versions of a specific gene?
alleles
66
True or false: Homologous chromosomes may carry the same or different alleles.
True
67
What is the ploidy of a cell?
The number of complete chromosome sets it contains.
68
What is the ploidy of humans and what does it mean?
2n. They have two homologs of each chromosome , and two alleles of each gene.
69
What crops are hexaploid plants?
bread wheat, oats, kiwifruit
70
What is the ploidy of cells produced by mitosis?
The same as the original cell (2n in humans)
71
What is the ploidy of cells produced by meiosis?
Half of the original number of chromosomes (n in humans)
72
What is a reduction division?
A division that reduces the number of chromosomes
73
What does meiosis allow for in relation to the number of chromosomes in an organism?
It allows organisms to maintain the constant number of chromosomes from generation to generation.
74
Meiosis evolved from ______.
Mitosis
75
How many gametes are produced from meiosis?
4
76
What is the goal of meiosis I?
To separate homologous chromosomes into different cells.
77
How does meiosis I insure that homologous chromosomes are not separated into the same cell?
Homologous chromosomes line up during metaphase I, and are later pulled apart.
78
What happens during homologous synapse?
Two pairs of non-sister chromatids are brought close together and are held there by a network of proteins called the synaptonemal complex.
79
What happens during crossing over?
Chromosomal segments are swapped between adjacent homologs (also called recombination)
80
What are the characteristics of chromosomes produced by meiosis I?
Replicated (sister chromatids) and haploid
81
What are the characteristics of cells produced by meiosis II?
Unreplicated and haploid
82
What is the key difference between meiosis and mitosis?
Homologous chromosomes pair in meiosis, but not in mitosis.
83
How does meiosis lead to genetic variation?
Through independent assortment of chromosomes and crossing over
84
What does crossing over produce?
New combinations of alleles on the same chromosome
85
Is self fertilization sexual or asexual reproduction?
Sexual reproduction. It still leads to genetic variation
86
What is outcrossing?
Gametes from different individuals combine to form offspring
87
What kind of offspring does asexual reproduction produce?
Clones (genetically identical to one another as well as the parent)
88
What is purifying selection?
Natural selection against deleterious alleles
89
What does purifying selection do?
Steadily reduces the numerical advantage of asexual reproduction
90
What is the Changing-Environment Hypothesis?
Offspring that are genetically different from their parents are more likely to survive and produce offspring if the environment changes. Offspring that are genetically identical to their parents are less likely to survive and produce offspring if the environment changes.
91
Does exposure to evolving pathogens favor outcrossing?
Yes
92
What is essential for the health of a population in resisting infectious diseases?
Genetic diversity
93
What is a nondisjunction?
When a mistake in meiosis occurs, causing two gametes to have an extra copy of a chromosome, and two gametes lacking a copy of a chromosome.
94
What is a trisomy?
When a gamete has an extra copy of a chromosome
95
What is a monosomy?
When a gamete lacks a copy of a chromosome
96
What are aneuploid zygotes?
Zygotes with too few or too many chromosomes
97
When do aneuploid zygotes typically survive?
When the aneuploidy involves chromosome 21, producing down syndrome, or when it involves sex chromosomes
98
How do bacteria divide?
Through binary fission
99
What does a nucleotide consist of ?
A phosphate group, a 5-carbon sugar, and a nitrogenous base
100
What connects nucleotides?
Phosphodiester linkages
101
What type of bond connects two strands of DNA?
Hydrogen bonds between nitrogenous bases
102
What are nucleoside triphosphates used for? What type of reaction is this?
DNA and RNA synthesis, exergonic reaction
103
What does each double helix of DNA consist of after replication?
One old strand and one new strand
104
What is daughter DNA?
New DNA after replication that are identical to each other and to the parent molecule
105
What does the precise copying of DNA strands allow for?
The transfer of genetic information from parent cell to daughter cells
106
What is the origin of replication?
A DNA sequence that can bind an initiator protein, where replication is initiated.
107
How many origins of replication do bacterial chromosomes have?
One
108
How many origins of replication do eukaryotic chromosomes have?
Multiple
109
A __________ _____ forms in a chromosome that is being replicated.
replication bubble
110
What is a replication fork?
An active area where DNA replication takes place
111
What is the enzyme that catalyzes DNA synthesis?
DNA polymerase
112
What direction does DNA synthesis always proceed in?
5' -----> 3'
113
What enzyme separates DNA strands (breaks hydrogen bonds)?
Helicase
114
What enzyme relives supercoils induced by helicase by cutting and resealing DNA strands?
Topoisomerase
115
What proteins prevent re-association of strands and stabilize them?
Proteins called SSBPs
116
What is the only way DNA polymerase can add a new nucleotide?
When a pre-existing nucleotide is present
117
What is a primer?
A short single strand of RNA
118
What is required in order for DNA polymerase to start DNA replication (besides pre-existing nucleotides)?
A primer
119
What is primase and what does it do?
A type of RNA polymerase that synthesizes primers for DNA replication
120
What is the leading strand?
Synthesis of new DNA is continuous and only one RNA primer is needed
121
What is the lagging strand?
Synthesis of new DNA is discontinuous and many RNA primer are needed
122
What are Okazaki fragments?
Short, discontinuous fragments found on the lagging strand
123
What enzyme removes ribonucleotides of the RNA primer and replaces them with deoxyribonucleotides?
DNA polymerase I
124
What enzyme joins adjacent deoxyribonucleotides with a phosphodiester linkage (closes the gaps in the lagging strand)?
DNA ligase
125
What shape are chromosomes in prokaryotes?
circular
126
What shape are chromosomes in eukaryotes?
linear
127
What is the probability that DNA polymerase will insert and incorrect base?
1 in every 100,000
128
How does DNA polymerase III prevent mistakes?
They proofread. When the enzyme finds a mismatch, it pauses and removes the mismatched base that was just added.
129
What are exonucleases?
Enzymes that work by cleaving nucleotides one at a time from the end of a polynucleotide chain. They make cuts at the end of a DNA strand.
130
Why is DNA polymerase III able to remove mismatched nucleotides (not how)?
One of the enzyme subunits has exonuclease activity.
131
What does endonuclease do?
Cuts in the middle of a DNA strand
132
What is the probability of inserting an incorrect base with the proofreading process of DNA polymerase III?
1 in 10,000,000
133
How are errors left after the DNA polymerase III proofreading system repaired?
By the mismatch repair (MMR) system
134
When does mismatch repair occur?
After DNA synthesis is complete
135
How does the mismatch repair system work?
Two nicks in the DNA are made around the mistake (including multiple correct nucleotides), the section of DNA is released, resynthesized, and ligase fills the gaps
136
What can cause DNA to become broken or altered?
Various chemical (carcinogens), x-ray radiation, and UV light
137
What can UV radiation cause in DNA?
Thymine dimers
138
What are thymine dimers?
Bonds that form between adjacent thymine bases. This causes a kink in the DNA strand
139
How are thymine dimers repaired?
Through nucleotide excision repair (functions the same way as the MMR system)
140
What is Xeroderma Pigmentosum (XP)?
A rare autosomal recessive disease in humans that causes extreme sensitivity to UV light.
141
What causes Xeroderma Pigmentosum (XP)?
Mutations in the nucleotide excision repair system
142
Where does protein synthesis take place?
In the cytoplasm through ribosomes
143
What can a change in DNA sequence lead to?
A change in protein structure
144
What can a change in protein structure lead to?
A change in phenotype
145
Why do different cells throughout the body have different functions when they all contain the same genes?
Different genes are expressed in different cells. Only selected genes are transcribed in a cell, resulting in different cells containing different proteins.
146
How does RNA synthesis occur?
RNA polymerase separate two strands of DNA by breaking the hydrogen bonds between complementary nucleotides. It the adds ribonucleotides that are complementary to DNA nucleotides.
147
What is the template strand in RNA synthesis?
The stand of DNA being copied
148
What is the coding strand in RNA synthesis?
The strand that is not being copied. It is early identical to the RNA being produced, besides U and T
149
True or false: RNA polymerases do not require primer to begin transcription.
True
150
What are promoters?
Special segments of DNA that initiate transcription
151
Are promoters transcribed?
No, they just recruit RNA polymerase
152
What is the +1 site?
Where transcription begins
153
Where is the promoter in relation to the +1 site?
Upstream
154
What is the downstream sequence?
The segment of DNA that will be transcribed
155
What are the two key regions of bacterial promoters?
The -10 box and the -35 box
156
What is the first stage of transcription?
Initiation
157
What determines the direction of transcription? How?
Sigma determines the direction of transcription by binding to a promoter in a specific way.
158
What happens to sigma once initiation of transcription is completed?
It dissociates from the core enzyme
159
What organisms have more diverse and complex series of promoters, prokaryotes or eukaryotes?
Eukaryotes
160
What is the TATA box?
A unique sequence found in eukaryotes, centered about 30 base pairs upstream form the transcription site.
161
What happens during the initiation phase of transcription in eukaryotes?
Basal transcription factors bind to the DNA promoter
162
How does sigma initiate transcription in bacteria?
Sigma binds to the RNA polymerase, which acts as a regulatory factor. It guides RNA polymerase to specific promoter sequences on the DNA template strand. Sigma opens the DNA double helix, forming a transcription bubble, and the template strand is threaded through the active site. Sigma dissociates once initiation is complete
163
How do basal transcription factors initiate transcription?
They bind to the DNA promoter. They perform a similar function to sigma, but they are composed of many proteins.
164
What is sigma?
A protein subunit found in bacteria
165
What are basal transcription factors?
A group of proteins found in eukaryotes
166
What is the second phase of transcription?
Elongation
167
What happens during the elongation phase of transcription?
RNA polymerase moves along the DNA template and synthesized RNA in the 5' ----> 3' direction
168
What is the last phase of transcription?
Termination
169
What happens during the termination phase of transcription?
RNA polymerase encounters a transcription termination signal in the DNA template
170
What signals the end of transcription in bacteria?
The transcription termination signal codes for an RNA sequence that forms a hairpin structure. The hairpin causes the RNA polymerase to separate from the RNA transcript.
171
What are introns?
The non-coding regions of eukaryotic genes that interrupt the protein coding regions
172
What are exons?
The protein coding regions of genes
173
What is pre-mRNA?
The product of transmission that is an immature primary transcript. This must be processed into a mature transcript before being translated.
174
How are introns removed?
Through splicing
175
What is a spliceosome?
An enzymes that catalyzes the splicing reaction that removes introns
176
What is the spliceosome made of?
Proteins and RNA
177
What is another way besides splicing that primary RNA transcripts can be processed?
By adding a 5' cap and a poly(A) tail
178
What does the 5' cap do?
It serves as a recognition signal for the translation machinery and it protects mRNA degradation
179
What does the poly(A) tail do?
It extends the life of an mRNA by protecting it from degradation
180
How does mRNA start?
With a 5' cap and a 5' untranslated region
181
How does mRNA end?
With a 3' untranslated region and a poly(A) tail
182
How many amino acids are used to build proteins?
20
183
How many different amino acids are possible (not all are used)?
64
184
What is a codon?
A three-base code. It acts as a "word" in the genetic code.
185
What are traits of the genetic code?
It is redundant, non-overlapping, unambiguous, nearly universal, and conservative
186
What is the start codon?
AUG
187
What are the three stop codons?
UGA, UAA, and UAG
188
What direction do ribosomes read codons in?
5' -----> 3'
189
What is a ribosome?
A multimolecular complex consisting of proteins and rRNA. It is made of two subunits
190
What do ribosomes do?
Perform translation. They move along mRNA and read codons, one at a time. It synthesizes proteins from amino acids based on information from mRNA, and it catalyzes the formation of peptide bonds.
191
What are tRNAs?
Relatively short RNA molecules
192
What is the shape of tRNA molecules and what causes this shape?
An upside down L caused by hydrogen bonds between nucleotides
193
What sequence is at the end of tRNA molecules and what end is it on?
CCA on the 3' end
194
What is an anticodon?
Three base pairs on the bottom loop of a tRNA molecule that can bind to an mRNA codon
195
What determines the amino acid that is added to CCA on a tRNA molecule?
The anticodon
196
How many tRNAs are there? How many different codons?
40 tRNAs and 61 codons
197
What is the wobble hypothesis?
The anticodon of tRNAs can bind to a codon whose third position requires a nonstandard base pairing, as long as the first two ribonucleotides can bond.
198
How are amino acids attached to tRNAs?
By the enzyme aminoacyl-tRNA synthase. This requires ATP.
199
How is aminoacyl-tRNA synthase able to catalyze the reaction between amino acids and tRNAs?
Aminoacyl-tRNA synthases recognize the overall shape of tRNA and can recognize multiple tRNAs for the same amino acid
200
What are the two subunits that make up ribosomes?
Large and small
201
What is each subunit of a ribosome made of?
Many proteins and rRNAs (ribosomal RNAs)
202
What does the small subunit of a ribosome do?
It holds the mRNA in place during translation
203
What does the large subunit do?
It is where peptide bonds form
204
What end of a polypeptide are amino acids always added to?
The C-terminus
205
What is the A site of a ribosome?
The acceptor site
206
What is the P site of a ribosome?
The peptidyl site
207
What is the E site of a ribosome?
The exit site
208
What does the A site do?
It holds an aminoacyl tRNA
209
What does the P site do?
It holds the tRNA with a growing polypeptide attached
210
What does the E site do?
It holds a tRNA that will exit
211
What is the first phase of translation?
Initiation
212
What happens during the initiation phase of translation?
Translation begins with AUG, the initiator tRNA binds to the start codon, and the large subunit binds to the small subunit
213
What is the Shine-Dalgarno sequence?
A ribosome binding site that precedes the start codon, that is complementary to a section of one rRNA in the small ribosomal subunit (only found in bacteria)
214
How does translation start in eukaryotes (how is the ribosome recruited)?
The 5' cap recruits the small subunit to mRNA and the ribosome begins scanning for the start codon
215
What is the second phase of translation?
Elongation
216
What are the three steps of the elongation phase of translation?
1. Arrival of the aminoacyl tRNA
2. Peptide bond formation
3. Translocation
217
Where do peptide bonds form between amino acids during translation?
Between the P and A site
218
Is a ribosome an enzyme or a ribozyme?
A ribozyme
219
What is a ribozyme?
An enzyme with catalytic activity
220
What happens during the translocation step of elongation?
Elongation factors move the mRNA down the ribosome three nucleotides at a time, and the tRNAs move into the next site
221
What form of energy does the translocation step of elongation use?
GTP
222
What is the third phase of translation?
Termination
223
What happens during the termination phase of translation?
The A site encounters a stop codon, which causes a protein called a release factor to enter the site. The release factor binds to a stop codon, the polypeptide and uncharged tRNAs are released, and ribosome subunits separate.
224
How do transcription and translation occur in bacteria?
They happen at the same time
225
What gene is associated with the early-onset form of Parkinson's disorder?
SNCA
226
Why are different genes expressed in different cells?
Different genes have different promoters, and different transcription factors are present in different cells.
