DNA structure, replication, and protein synthesis Flashcards
1
Q
what did Frederick Griffith do
A
experiment where he had living S and R cells and heated them to see if a mouse will live or die
2
Q
conclusion of Frederick Griffith’s experiments
A
living R bacteria transformed into deadly S bacteria by unknown, heritable substance
3
Q
Oswald Avery discovery
A
the transforming agent in Griffith’s experiments was DNA
4
Q
proteins radiolabel
A
S
5
Q
DNA radiolabel
A
P
6
Q
bacteriophages
A
virus that infects bacteria
7
Q
bacteriophages composed of
A
DNA
protein
8
Q
who discovered bacteriophages
A
Hershey and Chase
9
Q
Hershey and Chase conclusion
A
DNA entered infected bacteria 🡪 DNA must be the genetic material!
10
Q
Chargaff’s Rules
A
DNA composition varies between species
Ratios: %A = %T and %G = %C
11
Q
who did Rosalind Franklin work with and what did they discover
A
Maurice Wilkins
X-ray crystallography = images of DNA
Provided measurements on chemistry of DNA
12
Q
James Watson & Francis Crick discovered
A
double helix by building models to conform to Franklin’s X-ray data and Chargaff’s Rules
13
Q
structure of DNA
A
“Backbone” = sugar + phosphate
“Rings” = nitrogenous bases
14
Q
which nitrogenous bases are purines
A
adenine
guanine
15
Q
which nitrogenous bases are pyrimidines
A
thymine
cytosine
16
Q
nitrogenous bases pairing
A
purine + pyrimidine
A = T
G Ξ C
17
Q
what bonds are between the nitrogenous bases and how do they work
A
hydrogen bonds
holds molecule together like a zipper
18
Q
what direction do the DNA strands run in
A
antiparallel
one strand (5’🡪 3’), other strand runs in opposite, upside-down direction (3’ 🡪 5’)
19
Q
prokaryotic DNA features
A
Double-stranded
Circular
One chromosome
In cytoplasm
No histones
Supercoiled DNA
20
Q
eukaryotic DNA
A
Double-stranded
Linear
Usually 1+ chromosomes
In nucleus
DNA wrapped around histones (proteins)
Forms chromatin
21
Q
replication definition
A
Making DNA from existing DNA
22
Q
3 alternative models of DNA
A
conservative
semiconservative
dispersive
23
Q
Meselson & Stahl experiment
A
bacteria cultured in medium with 15N (heavy isotope)
bacteria transferred to medium with 14N (lighter isotope)
24
Q
Meselson & Stahl experiment results
A
less dense floated towards top, more dense was at bottom
25
what type of DNA model is replication? why
semiconservative
parent molecule separates and replicated into "daughter" DNA molecules, consisting of one parental strand and one new strand
26
7 major steps of DNA replication
Helicase: unwinds DNA at origins of replication
Initiation proteins separate 2 strands 🡪 forms replication bubble
Primase: puts down RNA primer to start replication
DNA polymerase III: adds complimentary bases to leading strand (new DNA is made 5’ 🡪 3’)
Lagging strand grows to create Okazaki fragments
DNA polymerase I: replaces RNA primers with DNA
DNA ligase: seals fragments together
27
job of helicase
unwinds DNA at origins of replication and creates replication forks
28
job of primase
synthesizes RNA primer at 5' end of leading strand and of each Okazaki fragment of lagging strand
29
job of DNA polymerase III
adds nucleotides in 5’🡪3’ direction on leading strand
30
Okazaki Fragments
Short segments of DNA that grow 5’🡪3’ that are added onto the Lagging Strand
31
DNA ligase purpose
seals together fragments
32
single strand binding protein job
binds to and stabilizes single-stranded DNA until it can be used as a template
33
job of topoisomerase
relieves "overwinding" strain ahead of replication forks by breaking, swiveling, and rejoining DNA strands
34
job of DNA polymerase I
removes RNA nucleotides of primer from 5' end and replaces them with DNA nucleotides
35
what proofreads as nucleotide bases are added?
DNA polymerase
36
mismatch repair
special enzymes fix incorrect pairings
37
nucleotide excision repair
Nucleases cut damaged DNA
DNA poly and ligase fill in gaps
38
how common are pairing errors
1 in 100,000 nucleotides
39
how common are complete DNA errors
1 in 10 billion nucleotides
40
Problem at the 5’ End
DNA poly only adds nucleotides to 3’ end
No way to complete 5’ ends of daughter strands
Over many replications, DNA strands will grow shorter and shorter
41
Telomeres
repeated units of short nucleotide sequences (TTAGGG) at ends of DNA
“cap” ends of DNA to postpone erosion of genes at ends (TTAGGG)
42
telomerase
enzyme that adds to telomeres
43
examples of telomerase
eukaryotic germ cells
cancer cells
44
what two ways do genes specify proteins
transcription
translation
45
gene expression
process by which DNA directs the synthesis of proteins (or RNAs)
46
old idea of gene expression
one gene-one enzyme hypothesis
Function of a gene = dictate production of specific enzyme
47
who proposed the old idea of gene expression? what did they do to test it
Beadle & Tatum – mutant mold experiments
48
newer idea of gene expression
one gene-one polypeptide hypothesis
49
most accurate idea of gene expression
one gene-one RNA molecule (which can be translated into a polypeptide)
50
basic flow of genetic info
dna to rna to protein
51
basic transcription sequence
dna to rna
52
basic translation sequence
rna to protein
53
what is the role of the ribosome in the flow of genetic information
site of translation
54
DNA properties
Nucleic acid composed of nucleotides
Double-stranded
Deoxyribose=sugar
Thymine
Template for individual
55
RNA properties
Nucleic acid composed of nucleotides
Single-stranded
Ribose=sugar
Uracil
Many different roles!
one gene = one rna molecule
56
pre-mRNA
precursor to mRNA, newly transcribed and not edited
57
mRNA
the edited version; carries the code from DNA that specifies amino acids
58
tRNA
carries a specific amino acid to ribosome based on its anticodon to mRNA codon
59
rRNA
makes up 60% of the ribosome; site of protein synthesis
60
snRNA
small nuclear RNA; part of a spliceosome. Has structural and catalytic roles
61
srpRNA
a signal recognition particle that binds to signal peptides
62
RNAi
interference RNA; a regulatory molecule
63
ribozyme
RNA molecule that functions as an enzyme
64
3 factors of the genetic code
For each gene, one DNA strand is the template strand
mRNA (5’ 🡪 3’) complementary to template
codons code for amino acids in polypeptide chain
65
codon
mRNA triplets
66
how many different codon combos are there
64
67
Redundancy in the genetic code
1+ codons code for each of 20 AAs
68
reading frame in the genetic code
groups of 3 must be read in correct groupings
69
is the genetic code universal?
yes
all life forms use the same code
70
Transcription unit
stretch of DNA that codes for a polypeptide or RNA (eg. tRNA, rRNA)
71
RNA polymerase:
Separates DNA strands and transcribes mRNA
72
what direction does mRNA elongate in
5' to 3' direction
73
what replaces thymine when pairing to adenine in mRNA
uracil
74
what does the RNA polymerase attach to?
promoter
75
what does the RNA polymerase stop at?
terminator
76
promoter
start of gene
77
terminator
end of gene
78
3 steps of transcription
initiation
elongation
termination
79
what is transcription
the DNA directed synthesis of RNA
80
what happens in eukaryotes during initiation (transcription)
TATA box = DNA sequence (TATAAAA) upstream from promoter
Transcription factors must recognize TATA box before RNA polymerase can bind to DNA promoter
81
what happens during elongation (transcription)
RNA polymerase adds RNA nucleotides to the 3’ end of the growing chain (A-U, G-C)
As RNA polymerase moves, it untwists DNA, then rewinds it after mRNA is made
82
what happens during termination in Eukaryotes (transcription)
pre-mRNA is formed as RNA polymerase transcribes a terminator sequence in DNA, then mRNA and polymerase detach
83
what happens for prokaryotes in termination (transcription)
mRNA is ready for use
84
what happens in eukaryotic cells after transcription?
modifies RNA
85
Additions to pre-mRNA
5’ cap (modified guanine) and 3’ poly-A tail (50-520 A’s) are added
86
job of pre-mRNA
Help export from nucleus, protect from enzyme degradation, attach to ribosomes
87
splicing
introns cut out, exons joined together
88
what does pre-mRNA have
introns and exons
89
intron
non-coding sequence
some regulate gene activity
90
exon
code for amino acid
91
snRNP stands for
small nuclear ribonucleoproteins
92
what are snRNPs composed of
snRNA + protein
93
snRNP pronunciation
snurps
94
what do snRNPs recognize
splice sites
95
spliceosomes are made of
snRNP + protein
96
what do spliceosomes do
catalyze the process of removing introns and joining exons
97
ribozyme means that
RNA acts as enzyme
98
Alternative RNA Splicing produces
different combos of exons
99
20,000 genes have how many peptides?
100,000
100
can one gene made more than one polypeptide?
yes
101
translation is
the RNA directed synthesis of a polypeptide
102
components of translation
mRNA = message
tRNA = interpreter
Ribosome = site of translation
103
where is tRNA transcribed
nucleus
104
is tRNA specific to each amino acid?
yes
105
job of tRNA
transfers amino acids to ribosomes
106
anticodon
pairs with complementary mRNA codon in tRNA
107
wobble
Base-pairing rules between 3rd base of codon & anticodon are not as strict
108
Aminoacyl-tRNA-synthetase
enzyme that binds tRNA to specific amino acid
109
ribosomes are made of
rRNA + protein
2 subunits
110
where are ribosomes made
nucleolus
111
A site
holds amino acids to be added
112
P site
holds growing polypeptide chain
113
E site
exit site for tRNA
114
basic steps of translation
initiation
elongation
termination
115
what happens in initiation (translation)
Small subunit binds to start codon (AUG) on mRNA
tRNA carrying Met attaches to P site
Large subunit attaches
116
what happens during elongation (translation)
codon recognition
peptide bond formation
translocation
repeat
117
what happens during codon recognition
tRNA anticodon matches codon in A site
118
what happens during peptide bond formation
amino acids in A site forms bond with peptide in P site
119
what happens during translocation
tRNA in A site moves to P site; tRNA in P site moves to E site (then exits)
120
what happens during termination (translation)
Stop codon reached and translation stops
Release factor binds to stop codon; polypeptide is released
Ribosomal subunits dissociate
121
polyribosomes
A single mRNA can be translated by several ribosomes at the same time
122
Protein Folding
During synthesis, polypeptide chain coils and folds spontaneously
chaperonin helps
123
job of chaperonin
protein that helps polypeptide fold correctly
124
free ribosomes
synthesize proteins that stay in cytosol and function there
125
Bound ribosomes (to ER)
make proteins of endomembrane system (nuclear envelope, ER, Golgi, lysosomes, vacuoles, plasma membrane) & proteins for secretion
Uses signal peptide to target location
126
Signal peptide
20 amino acids at leading end of polypeptide determines destination
127
Signal-recognition particle (SRP)
brings ribosome to ER
128
what can point mutations affect
proteins structure and function
129
Mutations
changes in the genetic material of a cell
130
large scale mutation
chromosomal; always cause disorders or death
131
examples of large scale mutations
nondisjunction, translocation, inversions, duplications, large deletions
132
point mutations alter
one base pair of a gene
133
Base-pair substitutions
replace 1 with another
134
missense
different amino acid
135
nonsense
creates a stop codon instead of an amino acid
136
frameshift
mRNA read incorrectly (does not read the codons correctly)
137
what does frameshift mutation produce
creates nonfunctional proteins
138
what are frameshift mutations caused by
insertions or deletions
139
silent mutations have
no effect
140
sickle cell disease is caused by
a genetic defect
141
sickle cell disease symptoms
anemia
pain
frequent infections
delayed growth
stroke
pulmonary hypertension
organ damage
blindness
jaundice
gallstones
142
how many humans carry sickle cell disease
5%
25% in some regions of Africa
143
life expectancy of people who have sickle cell disease
males: 42
females: 48
144
issue with sickle cells
hemoglobin forms long, inflexible chains
145
where does Transcription and translation happen in prokaryotes
cytoplasm
146
where is RNA/DNA in prokaryotes
cytoplasm
147
where does RNA poly bind in prokaryotes
directly to promoter
148
do prokaryotes have introns?
no
149
where does transcription and translation happen in eukaryotes
Transcription in nucleus; translation in cytoplasm
150
where is DNA/RNA in eukaryotes
DNA in nucleus, RNA travels in/out nucleus
151
where does RNA poly bind to in eukaryotes
TATA box and transcription factors
152
do eukaryotes have exons and introns
yes, cut out
153
gene
A region of DNA whose final product is either a polypeptide or an RNA molecule
