Bio Exam 2 Flashcards
(211 cards)
1
Q
Friedich Miescher (1860)
A
used a salt solution to wash pus off bandages. Treated pus with an alkaline solution and the cells would lyse and nuclei would precipitate out. He called the unique substance in the nuclei “nuclein”. It has a LOT of phosphorus in it. (the nuclein is now what we call DNA)
2
Q
Frederick Griffith
A
Scientist who worked with the bacteria Streptococcus pneumoniae in mice, with both the pathogenic and nonpathogenic strains (the R and S strains).
He discovered transformation: nonpathogenic bacteria had been transformed into pathogenic bacteria by an unknown heritable substance (DNA).
3
Q
Avery, McCarty, and MacLeod
A
Expanded Griffith’s experiment by thoroughly testing the S strain from dead mice. They determined that transformation cannot occur unless DNA is present and that DNA is the transforming substance
4
Q
Alfred Hershey and Martha Chase (1950s)
A
geneticists studying bacteriophage T2. They performed experiments showing that DNA is the genetic material of this phage.
5
Q
Erwin Chargaff
A
Reported three main rules regarding nitrogenous bases:
- Relative concentrations of the four nucleotide bases varied from species to species, but not within tissues of the same individual or between individuals of the same species.
- For each species the A = T and G = C. (the amount of A is equal to the amount of T, etc)
- Different species have equal amounts of purines (A+G) and pyrimidines (G+C), but different ratios of A+T to G+C specifically.
6
Q
Does the size of a genome (number of base pairs) indicate complexity?
A
nope nope nope
7
Q
James Watson and Francis Crick (1953)
A
proposed that DNA is made up of two strands, twisted around each other to form a right-handed helix/double helix, and that the two strands are anti-parallel. Figured this out with Rosalind Franklin’s Photo 51.
8
Q
Rosalind Franklin and Maurice Wilkins
A
used a technique called x-ray crystallography to study molecule structure. Created the photo called PHOTO 51 that showed the helical structure of the DNA molecule
9
Q
Sanger Sequencing of DNA
A
A method developed by Frederick Sanger that allows us to determine the sequence of DNA. Dye-labeled dideoxynucleotides are used to generate DNA fragments that terminate at different points. Then the fragments are all put together to determine the original sequence of the DNA.
10
Q
DNA
A
a polymer built of the monomer subunits adenine, thymine, cytosine, and guanine. Known as the substance of inheritance. Regarded as the most celebrated molecule of our time.
11
Q
Pathogenic strain
A
a smooth or S strain of bacteria
12
Q
Nonpathogenic strain
A
a rough or R strain of bacteria
13
Q
3’ DNA end
A
there is a hydroxyl group attached to the 3rd carbon
14
Q
5’ DNA end
A
there is a phosphate group attached to the 5th carbon
15
Q
Somatic cells
A
any cell that isn’t a sperm or egg cell. Get 2 copies from each chromosome, one from mom and one from dad, therefore they are diploid (2n).
16
Q
Gamete cells
A
sperm and egg cells. Get one copy of each chromosome since they are male and female specific, therefore they are haploid (n). THE ONLY HAPLOID CELLS IN THE BODY
17
Q
What are chromosomes composed of?
A
DNA AND HISTONE PROTEIN.
On a broader level, it’s composed 2 chromatids.
18
Q
Centrosome
A
An organelle that helps with cell division. Helps form the mitotic spindle.
19
Q
Centromere
A
The joining point for the two sister chromatids
20
Q
Telomere
A
nucleotides at the end of the chromosomes
21
Q
Chromatid
A
The two parts of the chromosome right after replication. One is called a chromatid, both together are called sister chromatids. They are the two arms that make the classic x shape of the chromosome
22
Q
Chromatin vs Chromatid
A
Chromatin: A complex of DNA, RNA, and histone proteins that makes up chromosomes. Organized into 4 fiber levels.
Chromatid: the two sister chromatids are the arms that make the classic x shape of the chromosome.
23
Q
Phosphodiester bonds
A
The bonds that hold nucleotides together ON ONE STRAND OF DNA
24
Q
Hydrogen bonds (role in DNA)
A
the bonds that hold nucleotides together BETWEEN STRANDS OF DNA
25
Base pairs
nitrogenous base pairs (A+T or C+G)
26
How many base pairs do humans have?
3 billion base pairs (so 6 billion nucleotides total)
27
How many genes to humans have?
From 20K to 25K genes
28
How similar is our DNA to all other humans?
99.9%
29
How many pairs/sets of chromosomes do humans have, and where do we get them from?
Humans have 23 pairs, so 46 total. You inherit one set of diploid
(2n) from each parent (23 from mom and 23 from dad).
30
Who is mtDNA (mitochondrial DNA) inherited from?
exclusively from the mom
31
How many bonds to A+T form?
two hydrogen bonds
32
How many bonds to C+G form?
three hydrogen bonds
33
How many base pairs does your smallest chromosome have?
48 million base pairs (so 96 million nucleotides total)
34
How many feet long is the DNA of a single cell?
6 feet long (2 meters)
35
Who is the sex of a child determined by and why?
The father determines the child's sex since males have XY chromosomes and females have XX. If the father donates an X chromosome then the child will be female, and if he donates a Y chromosome then the child will be male.
36
Which direction must DNA grow in?
The 5' to 3' direction (so new nucleotides must be added to the 3' end)
37
Chromatin
A complex of DNA, RNA, and histone proteins that makes up chromosomes. Organized into 4 fiber levels.
38
10 nm fiber level
The 1st fiber level/level of packaging. DNA (which starts as a 2 nm helix) wraps around histone proteins to form nucleosome "beads". The beads are linked together by linker DNA. This "beads on a string" structure is a 10 nm thick fiber.
39
30 nm fiber level
The 2nd fiber level/level of packaging. The nucleosomes coil into a thicker, 30 nm thick fiber
40
300 nm fiber level
The 3rd fiber level/level of packaging. The 30 nm The fiber folds into loops, making a 300 nm thick fiber.
41
700 nm fiber level
The 4th fiber level/level of packaging. The loops condense very tightly, creating a 700 nm thick chromatid fiber (the most condensed form of chromatin.). Keep in mind: ONE SINGLE chromatid is 700 nm, not two sister chromatids together.
42
What are histone proteins made of?
tons of basic/positively charged amino acids
43
Metaphase is the only stage of _____ where we see ________.
The only stage of mitosis where we see chromatids
44
Most chromatin is loosely packed in the nucleus during ________ and condenses prior to ________.
interphase, mitosis
45
Euchromatin
Loosely packed chromatin. The DNA that gets expressed
46
Heterochromatin
Densely packed chromatin. The DNA that does NOT get expressed.
47
Conservative DNA replication
A theoretical method of DNA replication. The parental DNA remains together, and the newly formed daughter strands are together.
48
Semiconservative DNA replication
The real method of DNA replication. Each of the two parental DNA strands acts as a template for new DNA that is synthesized; after replication, each double-stranded DNA includes one parental or “old” strand and one “new” strand.
49
Dispersive DNA replication
A theoretical method of DNA replication. Both copies of DNA have double-stranded segments of parental DNA and newly synthesized DNA interspersed.
50
Who determined that DNA replication uses the semi-conservative model?
Meselson and Stahl - 1958
51
How the parent DNA strand uses semiconservative replication
1. DNA separates into its two separate strands
2. Each strand generates an identical daughter strand and binds to it following the base-pairing rules
3. There are now 2 DNA double helixes, each with a parent strand and a daughter strand.
52
Origins of replication
the special sites of the DNA where the two strands are separated for DNA replication
53
Prokaryotic shape of DNA
circular
54
Eukaryotic shape of DNA
linear
55
How many origins of replications do prokaryotes have?
one
56
How many origins of replication do eukaryotes have?
thousands
57
Helicase enzyme
breaks apart/unzips the two strands of DNA/the double helix.
58
Topoisomerase
Relieves topological/supercoiling stress ahead of the replication fork, meaning it prevents overwinding
59
Single-strand binding proteins (SSBs)
Binds to the ssDNA keep the two strands from coiling back together after they are separated
60
DNA-Polymerase
Add nucleotides to the 3' end of the DNA by replacing the RNA primer with DNA. Basically it builds the new strands during replication
61
DNA ligase
cut/paste. Seals the gaps between the Okazaki fragments AND joins the fragments into a single DNA molecule
62
Primase
synthesizes short RNA primers
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RNA primer
a short stretch of RNA nucleotides (typically 5–10 bases long) that provides a starting point for DNA polymerase during DNA replication. The ONLY time RNA gets involved with DNA replication.
64
DNA polymerases cannot _______________, they can only _________________.
They cannot initiate the synthesis of a polynucleotide. They can only add nucleotides to the 3' end of the DNA.
65
Polymerase Chain Reaction (PCR)
A molecular technique widely used in labs to make BILLIONS of copies of DNA in a matter of hours. Occurs in three stages: denaturation, annealing, and elongation.
66
Denaturation
The two DNA strands are separated (denatured)
67
Annealing
primers attach (anneal) to each DNA strand
68
Elongation
dNTP (deoxynucleotide triphosphate) bases pair to each strand to extend (elongate) them out. Carried out by thermostable DNA polymerase.
69
The rate of PCRs
Every time the reaction is carried out, you get double the amount of DNA you started with. After n reactions you will have 2^n molecules of DNA
70
How is eukaryotic DNA replication different from prokaryotic replication?
Eukaryotic DNA has the enzyme telomerase and thousands of origins of replication. Prokaryotic DNA has no telomerase and only one origin of replication.
71
The error rate of DNA polymerases
1/10^10 (This means 1 mutation/error occurs every 10 billion base pairs)
72
The two enzymes that repair mismatched nucleotides
AP endonucleases - can remove one nucleotide at a time
NER (nucleotide excision repair) - can remove a whole stretch of nucleotides at one time
73
Nucleotide excision repair process
1. Base pair mismatches are detected after DNA replication
2. Nuclease (enzyme) cuts out the damaged stretches of DNA
3. DNA polymerase (enzyme) replaces the removed nucleotides with the correct ones
4. The gap is sealed by DNA ligase (enzyme)
74
Which nucleotide is dimerized upon UV damage?
Thymine. This means a covalent bond forms between two thymines next to each other on one DNA strand
75
The end replication problem...
The ends of eukaryotic chromosomal DNA...
1. Get shorter with each round of replication
2. does not have RNA primer present at the end
3. The Last RNA primer cannot be replaced with DNA
REMEMBER: prokaryotes don't have this problem since they have circular DNA!!
76
Telomeres
The protective caps (short stretches of nucleotides) at the ends of chromosomes that postpone the erosion of genes near the ends of DNA molecules (think of the aglet at the end of a shoelace).
Every time a cell divides, the telomeres get shorter, but they can be extended by telomerase.
Discovered by Dr. Elizabeth Blackburn.
77
Telomerase
The enzyme that catalyzes the lengthening of telomeres in germ cells. Only active in certain cells (GAMETES AND ADULT STEM CELLS, NOT FOUND IN ADULT SOMATIC CELLS), and only at certain stages of life. And only present in eukaryotic DNA since prokaryotic DNA is circular and has no "ends".
78
What happens to the chromosomes of germ cells every cell cycle?
They get shorter
79
Leading strand
The strand that is continuously synthesized during DNA replication because it's moving in the same direction as the replication fork.
80
Lagging strand
The strand that is discontinuously synthesized during DNA replication. Because it has to keep waiting for the double helix to open and add a new primer every time to add new nucleotides since it's being synthesized in the opposite direction that the replication fork is moving.
81
Okazaki fragments
The short fragments of DNA that are synthesized during lagging strand DNA replication
82
Summary of DNA replication process
START: 1 parent double helix of DNA
1. Helicase unwinds the DNA strands
2. On the leading strand, DNA polymerase adds the complementary nucleotides continuously
3. On the lagging strand, it has to add nucleotides in short fragments (Okazaki fragments) since it has to keep waiting for the helix to unwind more
4. Ligase joins the DNA fragments together
END: 2 helixes of DNA, each with one parent strand and one daughter strand
83
Nucleosomes
created when DNA wraps around histone proteins in the 10nm fiber
84
The foundation of the continuity of life
the reproduction of cells - the cell cycle
85
The cell cycle
a cell's life from the division of a single parent cell to the production of two genetically identical and DIPLOIDdaughter cells
86
Why do cells need to reproduce?
1. To make more organisms
2. Damage repair
3. Growth
4. Tissue renewal
5. To replicate DNA
87
When we grow, what is happening to our cells?
They are increasing in number (NOT SIZE usually)
88
Examples of cells growing or shrinking
- Fat and muscle cells can grow and shrink
- Cells change size with age or illness such as...
- Women's uterus shrinks after menopause
- Male's prostate gland enlarges with age
89
Tissue Renewal vs Wound Repair/Healing
tissue renewal REGENERATES new tissue to replace old tissue, while round repair SEALS damaged tissue with scar tissue
90
Examples of things that are regenerated by renewal
hair, nails, skin, bone, endometrium (mucus membrane in uterus), heart, liver, kidneys, fingertips, fingers
91
Cell division in prokaryotes
binary fission
92
Cell division in eukaryotes
mitosis
93
The genome of prokaryotes
consists of one double-stranded, circular DNA molecule
94
The genome of eukaryotes
consists of several linear double-stranded DNA molecules in the form of chromosomes
95
Binary fission
cell division in prokaryotes. The daughter cells are identical.
96
Filamenting temperature-sensitive mutant Z (FtsZ)
The protein that assists in binary fission by directing the formation of the septum needed to constrict and divide the cell in two and
97
Result of mitosis
Two genetically identical daughter cells with the same chromosome number as the original cell.
98
Are the cell cycle and mitosis the same?
No, mitosis is LESS THAN 10% of the (eukaryotic) cell cycle. Over 90% of the cell cycle is actually interphase.
99
Genome
a cell's total supply of DNA/genetic information
100
The DNA molecules along with proteins are organized into _________ after the last fiber stage?
chromatin/chromosomes (chromosomes are the highly condensed form of chromatin)
101
Homologous chromosomes
Pairs of chromosomes that form upon fertilization with one from each parent. For this reason the cells are diploid (2n).
102
What are genes and what do they do?
The functional units of chromosomes. Determine specific characteristics by coding for specific proteins.
103
Traits
variations of the characteristics determined by genes. Ex: hair color is a characteristic with traits that are blonde, brown, black, etc.
104
Karyotype
an image of an individual's complete collection of chromosomes. These chromosomes are UNDUPLICATED, they are NOT sister chromatids yet.
105
The four tenets of cell theory
1. All living things are made of cells
2. Cells are the smallest fundamental units of matter
3. Cells store hereditary information in DNA
4. All cells come from pre-existing cells
106
All organisms have to replicate their DNA before __________.
dividing
107
When are homologous chromosomes duplicated?
During interphase
108
What happens after homologous chromosome duplication?
The chromosomes are sister chromatids after duplication. They are eventually separated and placed in new daughter cells during cell division.
109
Interphase
the phase of the eukaryotic cell cycle that is the time for normal growth and preparation for cell division.
110
Mitotic phase
The phase of the eukaryotic cell cycle where
the cell divides. Consists of 2 phases:
1. Mitosis - division of the nucleus
2. Cytokinesis - division of the cytoplasm
111
How long is the human cell cycle?
24 hours
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G1 phase of interphase
Primary growth period. The cell doubles in size, the organelles duplicate, and the ribosomes, RNA, enzymes, etc. (all the building blocks required for DNA replication) are synthesized for the S phase.
113
S phase of interphase (synthesis phase)
DNA replication occurs. Identical copies of the DNA molecules (sister chromatids) are joined at the centromere. Centrosomes produce the mitotic spindle that moves chromosomes.
114
G2 phase of interphase
The cell replenishes its energy stores and synthesizes proteins necessary for chromosome manipulation and movement. After this stage, the cell is ready for mitosis.
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Summary of the stages of the cell cycle
START: 1 parent cell
Interphase G1 phase: cell doubles in size, organelles duplicate
Interphase S phase: DNA replication occurs
Interphase G2 phase: cell replenishes energy
Mitosis/Karyokinesis: division of the nucleus (5 stages)
Cytokinesis: division of the cytoplasm
END: 2 daughter cells
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Karyokinesis
division of the nucleus, also called mitosis
117
What is cytokinesis, and what does it occurs simultaneously with?
division of the cytoplasm that occurs simultaneously with telophase.
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Cytokinesis in animal vs plant cells
In animal cells: a cleavage furrow forms from the outside and moves inward.
In plant cells: a cell plate forms from the middle and moves outward.
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The M phase
Mitosis AND cytokinesis
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Which cell cycle checkpoint does NOT check for DNA damage?
The M checkpoint (it's only focused on spindle fibers attaching to the kinetochores
121
nuclear envelope
the double membrane around the nucleus of a eukaryotic cell
122
What is mitosis and what are its five stages?
Mitosis is division of the cell nucleus, also called karyokinesis.
The five stages are:
1. prophase
2. prometaphase
3. metaphase
4. anaphase
5. telophase
123
prophase
First, the nuclear envelope breaks down. Then the centrosomes begin migrating to opposite sides of the cell, extending microtubules as they go (that will later form the mitotic spindle). Lastly, sister chromatids coil tighter (aided by condensin).
124
Kinetochore
a special protein structure found in the centromere (center) of a chromosome (two sister chromatids)
125
Prometaphase
First, the mitotic spindle continues developing from the centrosomes.
Then the chromosomes (sister chromatids) develop kinetochores.
Last, the mitotic spindle attaches to the chromosome kinetochores and orients them to face opposite poles.
126
Metaphase
The mitotic spindle's fibers align the chromosomes down the equatorial plane of the cell.
The sister chromatids are still attached at this point but they are preparing to separate in the next phase, so they are called metaphase chromosomes.
127
equatorial plane/metaphase plate
an imaginary line down the center of the cell where the chromosomes line up during metaphase
128
Mitotic spindle
an apparatus of microtubules that divides (pulls) chromosomes from the parental cell into two daughter cells during mitosis. Formed by centrosome organelles.
129
Anaphase
The sister chromatids are pulled apart by the spindle fibers and move in opposite directions toward the centrosomes they are attached to. After this, the two poles have equivalent collections of chromosomes.
130
Telophase
The chromosomes decondense (unravel) now that they have reached their opposite poles. Then, a nuclear envelope forms around each set of chromosomes so there is a nucleus at each pole (one for each daughter cell when the cell divides). OCCURS SIMULTANEOUSLY WITH CYTOKINESIS
131
Summary of mitosis stages
Prophase - nuclear envelop breaks down/centrosomes migrate
Prometaphase - mitotic spindle forms and attaches to kinetochores
Metaphase - chromosomes are lined up on the equatorial plane
Anaphase - sister chromatids pulled apart
Telophase - two nuclear envelopes for around the separated chromosomes, forming two nuclei
132
the evolution of mitosis
Since prokaryotes preceded eukaryotes by billions of years, it is likely that mitosis evolved from bacterial cell division
133
Dinoflagellates
A type of unicellular protists in which the nuclear envelope remains intact during cell division
134
Diatoms
Unicellular protists, the diatoms where the nuclear envelope remains intact during cell division. Additionally, the microtubules form a spindle IN THE NUCLEUS instead of the cytoplasm.
135
Which unicellular eukaryotes have a cell division process that is an intermediate between binary fission and mitosis?
diatoms, dinoflagellates, and some yeasts
136
Why does cell cycle regulation occur?
to prevent a compromised cell from dividing
137
Where does the cell cycle regulation occur?
Near the end of G1, at the G2 to mitosis transition, and in metaphase of mitosis.
138
Cell cycle frequency for an embryo
once every 20 min or less
139
cell cycle time for skin cells
12-24 hours
140
cell cycle frequency for liver cells
once every 1-2 years
141
When do cells stop dividing in mature nerve and muscle cells?
they stop once they reach maturity
142
What is the main trigger that can initiate or inhibit the cell cycle?
Excess or deficiency of human growth hormones (HGH), can cause dwarfism or gigantism or other things like that
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G1 checkpoint
Checking to see if the cell is ready for DNA replication in the S phase. If its not ready, it moves to the G0 resting phase until conditions are better.
144
G2 checkpoint
Ensures that all chromosomes have been replicated properly and the replicated DNA isn't damaged. If something's wrong, the cell cycle is halted until the issue can be repaired.
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Mitotic checkpoint
Checking to see if all the kinetochores of the sister chromatids are firmly anchored to 2 spindle fibers (one on each side). The cell cycle will halt if needed until this is done.
146
G0 resting phase
occupied by non-dividing cells (cells not actively preparing to divide)
147
Cells that can permanently stay in the dormant/G0 phase:
cardiac, muscle, and nerve cells
148
Which type of cell can be in the G0 phase but can also re-enter the active cell cycle if the right signals are received?
liver cells
149
Why might some cells enter the G0 phase?
Due to environmental conditions such as availability of nutrients, or stimulation by growth factors
150
What is cancer characterized by?
uncontrolled cell growth
151
What do tumors result from?
When reproduction of mutated cells surpasses growth of normal cells
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Proto-oncogenes
normal genes that encode for positive cell cycle regulators. When mutated, they can become oncogenes. Oncogenes are the bad, cancerous genes. Proto-oncogenes are not dangerous, they should operate like normal genes.
153
Tumor suppressor genes
segments of DNA that encode for negative cell cycle regulators. When activated, they can prevent uncontrolled cell division. When mutated, they may not be able to stop the cell cycle.
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Role of P53
A tumor suppressor protein. Works at the G1 checkpoint!!
If a cell experiences minor DNA damage, P53 pauses the cell cycle to allow DNA repair.
If damage is severe and cannot be repaired: P53 triggers apoptosis (cell death) to prevent the cell from becoming cancerous.
155
Immortal cell line
An abnormal group of cells that proliferated indefinitely due to mutation. It is so mutated that scientists have not been able to create a single situation in which this cell cycle halts.
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The HeLa cell line
The oldest and most frequently used immortal cell line. Obtained from HEnrietta LAcks in 1951 who dies from cervical cancer.
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When are the three cell cycle checkpoints?
At the end of G1, at the G2/M transition, and
during metaphase (in the M phase)
158
The central dogma of life
DNA ---> RNA ---> Protein
159
How many genes are on chromosome 20?
1,361
160
Why is the order of nucleotides in DNA important?
Genes are the specific sequences of nucleotides in a specific order
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The smallest gene in the human genome
the SRY gene, 828 nucleotides (204 amino acids)
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Beadle and Tatum (1941)
Hypothesized that each gene encodes for a single enzyme. Based on this, they surmised that each gene would influence a specific step in a metabolic pathway.
While this was a groundbreaking discover, it is very much an oversimplification of what really happens with genes and protein synthesis. Created the famous "one gene, one enzyme" theory
163
Beadle and Tatum's experiment
They took spores from bread mold and exposed them to mutations (x-rays) to create random mutations in the spores. They grew the mutated spores on normal food. Some grew fine and some didn't. They then tested the defective mold by giving it different nutrients one by one. They found that some mold strains couldn’t make specific VITAMINS unless they were provided in the food.
This showed that each gene is responsible for making one enzyme, leading to their famous "one gene, one enzyme" hypothesis.
164
What we now know about genes and enzymes, beyond the one gene-one enzyme theory:
- All genes encode for proteins, but the proteins don't have to be enzymes.
- Some genes encode a subunit of a protein, not a whole protein.
- Some genes make non-coding RNAs (rRNA, tRNA, siRNA, miRNA, snRNA, etc.)
- ALTERNATIVE SPLICING
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Exon
a gene segment that codes for proteins
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Intron
a non-coding segment that gets removed before protein synthesis.
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Alternative splicing
A form of splicing in which exons are arranged in lots of different ways, allowing for a single gene to code for multiple proteins.
168
How are nucleotide sequences decoded?
by interpreting codons in a specific reading frame
169
Codon
a specific triplet of nucleotides in mRNA that codes for a specific amino acid during protein synthesis
170
How many different codons are there?
64
171
True or false: multiple codons can code for the same amino acid but one codon cannot code for several amino acids.
True
172
What does it mean that the genetic code is redundant?
multiple codons can code for the same amino acid (one AA can have more than one codon make it) because there are 64 codons for only 4-5 amino acids.
173
The three stop codons
UAA, UGA, UAG
(U Are Annoying, U Go Away, U Are Gone)
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The one unique start codon, and which amino acid it codes for
AUG, codes for methionine
175
Methionine
the first AA an any protein translation.
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Why is the genetic code nearly universal?
Because every living organism uses DNA, which means they all use the same nucleotides. This suggests that there is a common origin for all life on Earth, and that life likely evolved from an ancestral organism in which the same code was used.
177
A gene can be interpreted by reading the codons, however...
The codons must be read in the correct reading frame (the correct sequence of base triplets).
178
What must every reading frame START with?
AUG, the start codon that codes for methionine.
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The two basic processes by which DNA directs protein synthesis
transcription and translation
180
Timing and location of transcription and translation (gene expression) in prokaryotes
They occur simultaneously in the cytoplasm
181
Timing and location of transcription and translation (gene expression) in eukaryotes
They occur non-simultaneously, with transcription in the nucleus and translation in the cytoplasm
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In prokaryotes, transcription and translation occur ________, whereas in eukaryotes they occur _________.
simultaneously, non-simultaneously
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Transcription (overview definition)
A DNA template strand is transcribed, meaning it is used to synthesize a complementary mRNA strand. Accomplished with RNA polymerase.
184
Transcription initiation steps
1. Transcription factors bind to the promoter region of the gene to be transcribed.
2. The transcription factors recruit RNA polymerase and bind with it to form the initiation complex.
3. RNA polymerase recognizes the transcriptional start sequence and begins synthesizing the RNA transcript in a 5’ to 3’ direction.
185
Transcription elongation steps
1, RNA polymerase unwinds the DNA
(10-20 bases at a time)
2. RNA polymerase “reads” the DNA nucleotide on the template strand and attaches the complimentary RNA nucleotide.
3. The RNA nucleotide is joined to the previous one with a phosphodiester bond.
186
Transcription termination steps
1. RNA polymerases reaches and transcribes the termination sequence.
2. The RNA transcript (the mRNA template strand) is released by RNA polymerase.
3. RNA polymerase detaches from the DNA, officially ending transcription.
187
Prokaryotic transcription termination
Rho protein must travel along mRNA template strand (RNA transcript) and interact with RNA polymerase to terminate transcription.
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The FACT Complex
(FAcilitates Chromatin Transcription) removes and reassembles the nucleosomes as RNA polymerase synthesizes mRNA. Only used in eukaryotes.
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DNA template (antisense) strand
the DNA strand that is transcribed into mRNA during transcription. Runs 3'-5'.
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DNA partner (sense/coding) strand
the DNA strand that is NOT transcribed into mRNA during transcription. Runs 5'-3'.
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a common example of a method that helps signal transcription termination:
The formation of a "hairpin" structure in the RNA transcript
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Transcription termination in prokaryotes
After termination, the RNA is immediately ready for translation
193
Transcription termination in eukaryotes
After termination, the RNA needs additional processing before translation
194
SUMMARY OF TRANSCRIPTION INITIATION, ELONGATION, AND TERMINATION
Initiation - After RNA polymerase binds to the promoter, the DNA strands unwind, and the polymerase initiates RNA synthesis at the start point on the template strand.
Elongation - The polymerase moves downstream, unwinding the DNA and elongating the rNA transcript 5'---3'. In the wake of transcription, the DNA strands re-form a double helix.
Termination - Eventually, the RNA transcript is released, and the polymerase detaches from the DNA.
195
Prokaryotes do not require RNA transcript modification, which means...
RNA transcripts in prokaryotes can be translated immediately after being transcribed
196
Post-transcriptional processing in eukaryotes
The set of modifications that pre-mRNA undergoes after transcription and before translation to become mature mRNA.
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The modifications of post-transcriptional processing
- The 5' end of the pre-RNA receives a modified guanine (5’-methylguanosine cap)
- The 3’ end of the pre-RNA receives a poly-adenosine tail (3’ poly-A tail)
The cap and tail protect the RNA as it enters the cytoplasm and undergoes translation.
- Also, RNA splicing happens
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RNA splicing
The process of removing introns and joining together exons to form a mature mRNA
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Spliceosomes
specialized protein complexes that perform RNA splicing
200
Translation (overview definition)
The synthesis of a protein using the mRNA template from transcription. Occurs on ribosomes.
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The molecular components of translation
tRNA, mRNA, ribosome, polypeptide
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tRNA structure
Transfer RNA molecules all carry a specific amino acid on 1 end and have an anticodon on the other end.
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Which enzyme does tRNA use to attach its amino acid?
aminoacyl-tRNA synthetase
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mRNA
Messenger RNA. Directs the recruitment of tRNA molecules and production of the polypeptide. mRNA is bonded to the small subunit of the ribosome. Each codon in the mRNA is bonded to the anticodon of the tRNA.
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Ribosome structure
Two subunits: one large and one small.
Also, it houses three sites for tRNA to carry out the translation process: E, P, and A sites. They consist of rRNA and proteins.
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Where does translation occur?
in the ribosomes, in the cytoplasm of the cell
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Translation initiation steps
1. mRNA binds the SMALL ribosomal subunit.
2. The start codon is located.
3. The initiator tRNA binds to the start codon.
4. Energy is used to recruit and bind the LARGE ribosomal subunit.
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Translation elongation steps
A tRNA enters the A site and bonds its anticodon with the corresponding codon of the mRNA.
The growing polypeptide chain attached to the tRNA in the P site forms a peptide bond with amino acid attached to the tRNA in the A site.
mRNA is shifted further along, this causes the bonded tRNAs to shift sites. The tRNA in the P site breaks its bond with the mRNA and enters the E site. The tRNA in the A site is shifted to the P site as it now has the growing polypeptide chain attached.
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Translation termination steps
The stop codon in the mRNA is reached and recognized.
A release factor is recruited and binds to the stop codon causing the hydrolysis of the polypeptide from the tRNA.
This bonding and a bit of energy is utilized to cause the dissociation of the translation components.
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SUMMARY OF TRANSLATION INITIATION, ELONGATION, AND TERMINATION
Initiation - the mRNA and tRNA bind to the two units of the ribosome
Elongation - amino acids are bonded to one another, building the polypeptide chain out of the P site
Termination - a release factor binds to the stop codon and causes the translation components to dissociate
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The site for most post-translational processing
the endoplasmic reticulum (ER)
