Genetics Test 3 Flashcards
1
Q
DNA A
A
Unwinding the helix, initiator protein, binds to ORI causing confirmation change, causes helix to destabilize and open up, exposes ssDNA
2
Q
DNA helicase
A
Made of DNA B polypeptides, hexamer of subunits, subsequently recruits holoenzyme to bind replication fork and initiate replication, require energy supplies by hydrolysis of ATP-denatures hydrogen binds and stabilizes double helix
3
Q
Single stranded binding proteins (SSBP)
A
Stabilize the open confirmation of helix, bind specifically to single strands of DNA,
4
Q
DNA gyrase
A
Relieves coiled tension from unwinding of helix (member of the DNA topoisomerases) slide along ahead of helicase to relieve tension
5
Q
Primase: RNA polymerase
A
Synthesizes RNA primer, provides 3’-OH required by DNA polymerase III for elongation, (aka build little short segments of RNA, capable of starting with nothing)
6
Q
DNA polymerase I
A
Removes primer
7
Q
RNA priming
A
Universal phenomena found in everything with DNA
8
Q
Continuous DNA synthesis
A
Leading strand
9
Q
Discontinuous DNA synthesis
A
Lagging strand
10
Q
Okazaki fragments
A
The chunks of DNA that form from the lagging strand
11
Q
DNA ligase
A
Catalyzes formation of phosphodiester bonds and seals nicks and joins Okazaki fragments
12
Q
DNA clamp
A
Prevents core enzyme dissociation from template
13
Q
Proofreading
A
DNA polymerase exonuclease can go back and correct mistakes (3’-5’)
14
Q
Enzymes and proteins that are essential to DNA synthesis
A
DNA polymerase III, SSBPs, DNA gyrase, DNA helicase, RNA primers
15
Q
Shared features of eukaryotic and Bacterial DNA replication
A
Double strand unwound at ORI, replication forks, bidirectional synthesis, requires four triphosphates, primer
16
Q
Why is eukaryotic DNA replication more complicated
A
More DNA, linear chromosomes, DNA complexes with nucleotides
17
Q
Do eukaryotic organisms have one ORI or many?
A
Many, speeds up the process
18
Q
Autonomously replicating sequences (ARSs)
A
120 base pairs of consensus sequence (same sequence in all those places) in yeast
19
Q
Prereplication complex (pre-RC)
A
Assembles at replication ORIs, early GI phase of cell cycle, for controlled timing of DNA replication
20
Q
Does eukaryotic DNA replication have one polymerase or many?
A
Many
21
Q
Polymerase switching
A
Occurs once the primer is in place
22
Q
Telomeres
A
Inert chromosomal ends that protect intact eukaryotic chromosomes from improper fusion or degradation, long stretches of short repeating sequences preserve the integrity/stability of chromosomes
23
Q
Telomerase
A
Eukaryotic enzyme, adds repeats of six nucleotide sequence to 3’ end to fill gaps
24
Q
Ribonucleoprotein
A
RNA serves as template for synthesis of DNA complement (reverse transcriptase)
25
Telomerase activity and telomere length linked to....
Aging, cancer, other diseases
26
In most eukaryotic somatic cells telomerase is active or not active?
Not active
27
What cells maintain telomerase activity - immortalized
Stem cells and malignant cells
28
Homologous recombination
Genetic exchange at equivalent positions along two chromosomes with substantial sequence homology
29
Genetic recombination involves:
Endonuclease nicking, strand displacement and pairing with complement, ligation, branch migration, duplex separation
30
Gene conversion
Consequence of homologous recombination, characterized by nonreciprocal genetic exchange between two DNA molecules
31
Bacterial and viral chromosome components
Single nucleic acid
Largely devoid of associated proteins
Much smaller than eukaryotic
32
Bacterial chromosomes
Circular double stranded DNA compacted into nucleoid
33
Supercoiling
Closed circular molecules, more compact and sediment more rapidly
34
Topoisomerase
Enzymes that cut one or both DNA strands, wind or unwind helix before resealing ends
35
Polytene chromosomes
Represent paired homologs, NOT NORMAL, seen in interphase cells, found in tissues such as salivary, rectal, midgut, fruit flies
36
Polytene chromosomes definition
DNA of paired holologs undergoes many rounds of replication without strand separation or cytoplasmic division
37
Puff regions
Bulges where DNA has uncoiled that are visible manifestations of high level gene activity (transcription that produces RNA)
38
Lampbrush chromosomes
Large with extensive DNA looping, easily isolated from oocytes in diplotene stage or prophase I of meiosis (it's like a giant puff)
39
Chromatin
At interphase, eukaryotic chromosomes uncoil and decondense into a form called chromatin which is dispersed throughout the nucleus during interphase
40
Histones
Positively charged proteins associated with chromosomal DNA in eukaryotes, five main types
41
Nucleosome
A length of DNA coiled around a core of histones (resembles beads on a string) are condensed several times to form intact chromatids
42
Superhelix
The structure the DNA forms when it makes a nucleosome
43
Histone tails
Not packed into the folded histone domains, allows for remodeling since we can stick things/remove things from the tails
44
Acetylation
Changes the charge if the histone, to make them spread out
45
Methylation
Makes the histones stick together
46
Phosphorylation
Adds phosphate groups
47
Euchromatin
Uncoiled and active, appears unsustained during telophase
48
Heterochromatin
Condensed areas are mostly inactive, appears stained during interphase
49
Chromosome banding techniques
Differential staining along longitudinal axis of mitotic chromosome (resemble polytene chromosome bands)
50
C-Banding
Only centromeres take up stain
51
G-banding
Differential staining along length of each chromosome
52
Nomenclature for human chromosome banding
Based on g banding, nomenclature applied to X chromosome
53
Repetitive DNA sequences
Are repeated many times within eukaryotic chromosomes
54
Satellite DNA
Highly repetitive and consists of short repeated sequences, found in heterochromatic centromeric regions of chromosomes
55
Moderately repetitive DNA
Variable number tandem repeats (VNTRs), minisatelites
56
Variable number tandem repeats (VNTRs)
Repeating DNA sequences 15-100 bp long, found within and between genes
57
Micro satellites or STRs (short tandem repeats)
Tandemly repeated sequence, dispersed throughout genome
58
Short interspersed elements (SINES) and long interspersed elements (LINES)
Transposable sequences that are mobile and can relocate within genome, dispersed not tandemly repeated
59
Retrotransposons
Transposable elements generated via RNA intermediate (LINES)
60
Pseudogenes
Large number of single-copy noncoding regions
61
Unambiguous
Each triplet specifies only one amino acid
62
Degenerate
A given amino acid can be specifies by more than one triplet code
63
Start and stop signals
Triplets that initiate and terminate translation
64
Commaless
Once translation begins the codons move in sets of three, no commas
65
Nonoverlapping
Any single ribonucleotide within mRNA is part of one triplet
66
Colinear
Sequence of codons in a GENE is colinear (genes sequence in DNA matches RNA matches the rest of the strands)
67
Nearly universal
A single coding dictionary is used by viruses, prokaryotes, archaea, and eukaryotes
68
mRNA (messenger)
Serves as intermediate in transferring genetic information from DNA to proteins (carries from DNA to ribosome)
69
Triplet code
Provides 64 codons to specify 20 amino acids
70
Reading frame
Contiguous sequence of nucleotides
71
Frameshift mutation
Insertions or deletions shift reading frame and change codons downstream
72
Nonoverlapping
Genetic code reads three nucleotides at a time in continuous linear manner (during translation genetic code is nonoverlapping)
73
What is meant when it is said that the genetic code is degenerate?
Many amino acids specified by more than one codon (only tryptophan and methionine are encoded by a single codon)
74
The wobble hypothesis
The initial two ribonucleotides of triplet codes are often more critical than the third
75
Methionine (AUG) - initiator codon
Initial amine acid incorporated into all proteins
76
Termination codons
UAG, UAA, UGA, do not code for any amino acid, translation terminates when these codons are encountered
77
Nonsense mutations
Mutations that produce a stop codon internally in gene, translation is terminated and a partial polypeptide is produced
78
Phage MS2
Bacteriophage that infects E. coli
79
Mitochondrial DNA exemptions to universal genetic code:
Codon UGA encodes tryptophan in yeast and humans instead of termination, AUA encodes internal insertion of methionine instead of isoleucine
80
Overlapping genes
Single mRNA has multiple initiation points and creates different reading frames
81
ORF open reading frame (overlapping genes)
DNA sequence produces RNA with start and stop, series of triplet codons specify amino acids to make polypeptide
82
Transcription
RNA synthesized on DNA template
83
Promoters
Specific DNA sequences in 5' region upstream of initial transcription point
84
Consensus sequences
DNA sequences homologous in different genes of same organism
85
Chain elongation
Ribosomes are added to RNA chain, elongation proceeds under direction of core enzyme
86
Termination
Enzyme transverse entire gene until a termination nucleotide sequence is encountered
87
Transcription in eukaryotes
Occurs within nucleus, mRNA must leave nucleus for translation
88
Transcription factors
Scan/bind DNA, enhancers and silencers
89
RNA polymerase 1 makes...
rRNA in the nucleolus
90
RNA polymerase II makes
mRNA and snRNA in the nucleoplasm
91
TATA box
Core promoter element, determines transcription start site
92
Posttranscriptional modifications
Addition of 5' cap, addition of 3' tail, excision of introns
93
Introns
Regions of initial RNA transcript not expresses in amino acid sequence of protein
94
Exons
Sequence retained and expressed
95
Splicing
Introns are removed, exons are joined together in mature mRNA, mature mRNA is smaller than initial RNA
96
Self splicing RNAs
Self excision group I introns occurs in bacteria, lower eukaryotes, and higher in plants
97
Spliceosome
Pre-mRNA introns spliced out by spliceosome, reaction involves formation of lariat structure
98
Substitution editing
Identities of individual nucleotide bases are altered; prevalent in mitochondria and chloroplasts RNA derived in plants
99
Insertion/deletion editing
Nucleotides are added/deleted from total number of bases, prevalent in mitochondrial and chloroplasts RNAs
100
tRNAs transfer RNA
Adapt genetic information present as specific triplet codons in mRNA to corresponding amino acid
101
Ribosomes
Have an essential role in expression of genetic information
102
rDNA
rRNA genes, moderately repetitive DNA fraction present in clusters at various chromosomal sites
103
Structure of tRNA
Cloverleaf
104
Anticodon
tRNA has anticodon that complementarily base pairs with codon in mRNA
105
Aminoacylation: tRNA charging
Before translation can proceed, tRNA molecules must be chemically linked to respective amino acids
106
Three steps of translation of mRNA
Initiation, elongation, termination
107
Initiation
Initiation complex = small robosomal subunit + initiation factors + mRNA at codon AUG
108
Initiation factors
Small and large ribosomal subunits, mRNA molecule, GTP, charged initiator tRNA, Mg2+, imitation factors
109
Elongation
Both ribosomal subunits assembled with mRNA, forms P and A site
110
Termination
Signaled by stop codons in A site
111
GTP dependent release factors
Stimulates hydrolysis of polypeptide from peptidyl tRNA - released from translation complex
112
Polysomes or polyribosomes
mRNAs with several ribosomes translating at once, as mRNA passes through ribosome, it's free to associate with another small subunit
113
Where does transcription occur in eukaryotes?
Nucleus
114
Where does translation occur in eukaryotes?
Cytoplasm
115
Kozak sequence
Eukaryotic mRNAs contain luring (A or G) three bases upstream from AUG initiator codon, followed by a G
(A/NNAUGG
116
Translation in eukaryotes requires...
More factors of initiation, elongation, and termination
117
Are ribosomes in eukaryotes free floating?
Not all of them, usually associated with endoplasmic reticulum
118
Alkaptonuria and phenylketonuria
Result from mutations that lead to metabolic blocks
119
Phenylketonuria (PKU)
Phenylalanine hydroxylase is inactive in affected individuals, phenylalanine is not converted into tyrosine and enters cerebrospinal fluid, causing mental retardation
120
One gene:one enzyme hypothesis
George Beadle showed genes are directly responsible for synthesis of enzymes (purposely exposed neurospora to bad things trying to force mutations, partner was Tatum)
121
One gene: one polypeptide chain hypothesis
Nearly all enzymes are proteins - not all proteins are enzymes, proteins have subunit structure with two or more polypeptide chains
122
Sickle cell anemia
Recessive genetic disease, affected individuals are homozygous for the gene, makes the blood cells pointy and easier to clog passages, heterozygotes are carried but largely unaffected
123
Chemical differences between normal and sickle cell hemoglobin
HbS and HbA hemoglobin differ by single peptide fragment
124
Colinearity
Order of nucleotides in gene correlates directly with order of amino acids in corresponding polypeptide
125
Polypeptides
Precursors to proteins, amino acids assembled on and released from ribosomes as polypeptides
126
Proteins
Polypeptides folded up into a functional three dimensional conformation
127
Amino acids
Add to the diversity of proteins, carboxyl group on one side and amino acid on the other making it positive and negatively charged, and a r group which determines the overall reactivity of the amino acid and type of amino acid
128
Peptide bond
Dehydration reaction facilitates bond between carboxyl group of one amino acid and amino acid group of another
