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BMSC 220 post midterm > post midterm > Flashcards

post midterm Flashcards

1
Q

3 laws of inheritance (mendel)

A

1) Law of Dominance
2) Law of Segregation
3) Law of Independent Assortment

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2
Q

Law of dominance

A

allels can be dominant or recessive

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3
Q

Law of Segregation

A

separation of alleles @ the level of the gametes

  • Two alleles of a pair segregate or separate during gamete formation such that a gamete receives only one of the two factors
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4
Q

Law of Independent Assortment

A

The alleles of two different genes get sorted into gametes independently of one another (Mendel had selected traits that were on different chromosomes –> law not true when different genes are present on the same chromosome (passed on linked as a linkage group))

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5
Q

homologous chromosomes

A

chromosome from mom and chromosome for dad - code the same genes but may have different alleles on both

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6
Q

linkage group

A

if you have a particular trait, there may be another trait that is always associated with it

  • competes with the Law of Independent Assortment
  • different genes on the same chromosome can be passed on as a linkage group
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7
Q

Thomas Hunt Morgan

A

mutation recognized as mechanism for variation in populations

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8
Q

physical underpinning of the unit of inheritance

A

chromosomes

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9
Q

Genetic material in all
organisms

A

DNA

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10
Q

Building block for DNA

A

nucleotide

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11
Q

Nucleotide structure

A
  1. Phosphate
  2. Sugar (deoxyribose)
  3. Nitrogenous base (pyrimidine/purine)
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12
Q

pyrimidines

A

Thymine and Cytosine

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13
Q

purines

A

Adenine and Guanine

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14
Q

DNA structure

A
  • sugar-phosphate backbone (phosphodiester bonds between hydroxyl on C3 of sugar and phosphate group on C5 of phosphate)
  • anti-parallel strands
  • H-bonding between complimentary bases
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15
Q

chargaffs rule

A
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16
Q

The Watson-Crick-Franklin Proposal

A
  1. DNA is composed of two chains of nucleotides.
  2. These two chains form a spiral pair of right-hand helices.
  3. The two chains are antiparallel, they run in opposite directions.
  4. The sugar-phosphate backbone is the exterior of the molecule, and the bases are interior.
  5. Bases are perpendicular to sugar-
    phosphate backbone.
  6. DNA chains are held together by
    hydrogen bonds between bases (A pairs with T via 2 hydrogen bonds; Gand C pair via 3 hydrogen bonds)
  7. Double helix width 2nm (diameter)
  8. Pyrimidines always paired with
    purines.
  9. Only A-T and C-G pairs fit within
    double helix.
    10.Molecule has a major groove and a minor groove.
    11.Complete turn is 10 base pairs.
  10. Complementary base sequences on each of the 2 strands.
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17
Q

allele

A
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18
Q

crossover

A
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19
Q

During cell division, the nuclear material is organized into visible “threads” called

A

chromosomes (chromatids are not visible)

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20
Q

transposons

A

genetic elements that can move from one genome site to another

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21
Q

5’ end of dna

A
  • where the free phosphate is (lecture)
  • has the fifth carbon in the sugar-ring of the deoxyribose or ribose at its terminus
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22
Q

supercoiled dna

A
  • negative supercoiling: underwound (less than 10 base pairs in the complete turn) - compacts DNA and important in replication and transcription
  • positive supercoiling: overwound (more than 10)
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23
Q

topoisomerases

A

change the level of DNA supercoiling

  • Type 1: transient break in 1 strand of DNA duplex
  • Type 2: transient break in both strands of DNA duplex (can also interlink or separate circular DNA)
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24
Q

DNA denaturation

A

DNA strands coming apart after applying heat

  • heating causes an increase in UV light absorbance (absorbance depends on amount of base pairing)
  • Melting temperature (Tm): halfway through shift in absorbance from low to high
  • higher GC content (3 hydrogen bonds; stronger interaction) = higher Tm (more heat needed to separate)
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25
Q

DNA renaturation (reannealing)

A

Single-strand DNA reassociates

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26
Q

Nucleic acid hybridization

A

Complementary strands of
nucleic acids from different
sources –> hybrid molecules

  • DNA sequencing, cloning,
    amplification
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27
Q

PCR

A

Denature @ 95 - Anneal @ 68 - Elongate @ 72

  • need primers and dNTPs
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28
Q

3 different types of DNA sequences with different reannealing rates

A
  • Highly repeated fraction
  • Moderately repeated fraction
  • Non-repeated fraction
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29
Q

Highly repeated DNA sequences
(Tandem repeats)

A

Short sequences (few 100 nucleotides) + clustered + repeat over
and over again (arranged end-to-end ie. tandem); 1-10% of total DNA

Further subdivided:

  • Satelite DNAs: short sequences that evolve rapidly
  • Minisatelite DNAs: unstable, variable in population, DNA fingerprinting
  • Microsatelite DNAs: aka short tandem repeats; small clusters, implicated in genetic disorders
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30
Q

Fluorescence in situ hybridization
(FISH)

A
  • used to determine location of a gene/dna sequence on a chromosome/in genome
  • denaturing dna and using fluorescent labelled probe to anneal to it and identify location
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31
Q

Moderately Repeated DNA Sequences

A
  • variability in how many are present in the genome (20% to greater than 80% of total DNA depending on organism) and how frequently they are repeated (from a few times to tens of thousands of times)
  • Some sequences code for gene products like RNAs or histones
  • Most sequences lack coding function - interspersed throughout the genome (grouped into SI and ES (short interspersed elements or lines long interspersed elements)
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32
Q

Non-repeated DNA Sequences

A
  • include genes with Mendelian patterns of inheritance, localize to particular site on particular chromosome
  • DNA sequences that code for all proteins other than histones (globins, actins, myosins, collagens, tubulins, integrins, and most other proteins in a eukaryotic cell)
  • less than 1.5% of human genome
  • sequences not present in multiple copies (single copy)
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33
Q

polyploidization

A

more than 2 sets of chromosomes (as compared to haploid/diploid)

  • common in plants (getting FULL set of chromosomes from both mom and dad - no meiosis)
  • in animals: single celled embryo accidentally undergoes chromosome duplication and retains the DNA
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34
Q

Gene duplication

A

duplication of one or more copies of a gene or region of a chromosome - can occur through unequal crossing over

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35
Q

Unequal crossing over

A

Homologous chromosomes misalign and exchange genetic material at non-identical positions (results in one chromatid gaining extra genetic material (duplication) and the other losing it (deletion)) - role in evolution of multigene families (for example, protein families like alpha and beta tubulins)

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36
Q

transposition

A

particular dna sequences (transposable elements/transposons) could move around genome and insert into target sites randomly

  • transposase: enzyme encoded in transposon that cuts the transposon and helps in its target site insertion
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37
Q

eukaryotes have

A

transposons (cut and paste) and retrotransposons (copy and paste)

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38
Q

retrotransposons

A
  • get rna (transcription by RNA polymerase) –>
  • get cDNA (reverse transcription to form single stranded cDNA) –>
  • get double stranded DNA
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39
Q

human genome

A

20,000 genes

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40
Q

Alternative splicing

A

a single gene can encode a number of related proteins

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41
Q

explanation for small number of protein-Coding Genes in the Human Genome

A
  • Alternative splicing: a single gene can encode a number of related proteins
  • MicroRNAs: Noncoding RNAs (not coding for proteisn) that can have gene regulatory functions (can act on genes to produce different but related proteins)
  • Proteins work together as complex networks rather than individually
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42
Q

Comparative Genomics

A
  • if It’s conserved it must be important
  • best way to identify functional sequences –> compare genomes of different organisms
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43
Q

Intergenic genome

A

Majority of genome lies between protein coding genes

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44
Q

Exons

A

The coding regions of a gene that are spliced together to form the final mRNA and translate into proteins.

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45
Q

An event in which offspring are produced that have twice the number of chromosomes in each cell as their diploid parents is called

A

Both polyploidization and whole-genome duplication

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46
Q

nucleosome

[organization of the chromosome]

A

DNA wrapped around histone

  • nucleosomes further coil into a chromatin fiber, which further condense to form looped domains, which pack into chromosomes
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47
Q

nucleosomes

A

DNA + histone octamer (core complex)

  • 146 bp supercoiled DNA wraps around histone twice

Histone octamer

  • 4 histone heterodimers: 2 (H3+H4) + 2 (H2A + H2B)

Histone H1 (linker histone)

  • binds linker DNA (connecting diff nucleosomes to each other to form the chromatin fiber)
  • can be modified
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48
Q

histone structure

A
  • globular region (histone fold) - alpha helices of proteins
  • histone tail
  • minor groove of dna faces histone
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49
Q

histone tail

A
  • N-terminus of histone
  • projects beyond wrapped dna helix too
  • subject to modification
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50
Q

chromatin

A
  • 30 nm chromatin fiber loop diameter (can be 80-100nm too)
  • proteins involved in the nuclear scaffold might be creating dna loops (?)
  • loops maintained by COHESION (also holds replicated dna molecules together during mitosis)
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51
Q

packing ratio of DNA

A

10,000:1

  • chromosome length = 1 um
  • length of contained dna = 1 cm
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52
Q

Euchromatin

A

loosely packed chromatin (interphase)

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53
Q

Heterochromatin

A

Tightly packed chromatin

  • Constitutive heterochromatin
  • Facultative heterochromatin
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54
Q

Constitutive heterochromatin

A
  • always condensed; silent DNA (cuz so packed, its not available for the transcription machinery to get in there and transcribe genes - therefore FEW GENES)
  • highly repeated sequences
  • in centromeres, telomeres, distal arm of Y chromosome
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55
Q

Facultative heterochromatin

A
  • can switch between condensed and relaxed (can be inactivated - changes with time, varies from cell to cell)
  • example: X chromosome (Barr body) - throughout a woman’s lifetime, there will be one transcriptionally active X chromosome and one transcriptionally inactive X chromosome (inactive is Barr body)
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56
Q

barr body

A
  • heterochromatic clump
  • transcriptionally not active

x- inactivation process is random

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57
Q

Histone code hypothesis

A

the modification of histone tails decides whether the particular region of DNA that it is interacting with is euchromatin or heterochromatin

  • modification happens at N-termini of H3 and H4
  • different proteins interact with the histone tails after they are modified
  • methylation of H3 is responsible for the formation of heterochromatin
  • can be phosphorylation, acetylation, methylation, ubiquination

histone tail modifications can:

  • recruit non-histone proteins
  • alter interaction of neighbouring histones in their nucleosomes
58
Q

Correlation Between Transcriptional Activity and Histone Acetylation

A

Removal of acetyl groups from
H3 and H4 histones converts euchromatin to heterochromatin (more condensed state - replication and transcription machinery has no access - gene does not get transcribed)

59
Q

Karyotype

A

homologous chromosome pairs ordered according to size- pattern can be used to screen chromosomal abnormalities

60
Q

Telomeres

A

protective structures located at the ends of chromosomes

  • consist of repeated DNA sequences + protein caps
  • TTAGGG
  • Repeated ~ 500-5000 times in
    humans (same sequence in all vertebrates; similar sequences in most other organisms)
61
Q

Telomerase

A

solves the End-Replication Problem by adding repetitive nucleotide sequences (e.g., TTAGGG in humans) to the ends of telomeres - extends the telomere becoming shorter

  • Reverse transcriptase that
    synthesizes DNA from RNA
    template
  • Adds new repeat units to 3’ end of
    overhanging strand
  • Unlike most reverse transcriptases, contains the RNA template it uses
  • Once 3’ end is lengthened, conventional DNA polymerase can
    return 5’ end of complementary
    strand to previous length
62
Q

telomere importance

A
  • Required for complete
    replications of chromosome
  • Form caps that protect
    chromosomes from nucleases
    and other destabilizing
    influences
  • Prevent ends of chromosomes
    from fusing with one another
63
Q

centromere

A
  • sites of concavity (indentation)
  • tandemly repeated constitutive heterochromatin
  • centromeric DNA is the site of microtubule attachment during mitosis
64
Q

epigenetics

A

inheritance that is not encoded in DNA

  • Example: X-Chromosome Inactivation: In females (XX), one X chromosome is randomly inactivated in each cell to equalize gene dosage with males (XY). This inactivation is maintained in all daughter cells throughout the individual’s lifetime.
  • Epigenetic state may be reversed: X chromosomes reactivated prior to gamete formation (ensuring both X chromosomes are functional in the resulting egg cells)
  • twins with different longevity and disease susceptibility (due to epigenetic changes accumulating)
65
Q

interchromosomal interactions

A

distant genes can interact in response to physiological stimuli (like hormone treatment)

  • target genes repositioned into close physical proximity - genes physically move to sites within nucleus called TRANSCRIPTION FACTORIES (have transcription mahcinery)
66
Q

Topographically Associated Domains

A

DNA within region tends to
interact much more strongly
with DNA in same region

  • 100s kb (1 kb = 1000 bases)
  • nuclear compartmentalization example
67
Q

transcription

A

Process by which RNA is formed from a DNA template

68
Q

Translation

A

Process by which proteins are
synthesized in the cytoplasm
from an mRNA template

69
Q

Messenger RNA (mRNA)
▫ Intermediate molecule between
a gene and a polypeptide

A
70
Q

What kind of bond forms between the phosphate groups of the DNA backbone and the positively charged amino acid resides of the histones and helps to hold the molecules together?

A

Ionic bonds

(dna backbone is negative czu of phosphate group and histone has basic amino acids that give it positive charge)

71
Q

what is the packing ratio of DNA in mitotic chromosomes?

A

10,000:1

72
Q

What is chromatin that remains compacted during interphase called? This compacted, densely stained chromatin is found at the nuclear periphery.

A

Heterochromatin

Cuz (compacted chromatin fibres)

72
Q

central dogma

A

DNA to RNA to protein

73
Q

mRNA

A

formed after transcription from DNA template
- codes for proteins

74
Q

rRNA

A

80% of the RNA (most common form of RNA)

  • form the basic structure of the ribosome
  • catalyze protein synthesis
75
Q

tRNA

A

adaptors between mRNA and amino acids

  • bring in nucleic acid building blocks as we synthesize protein
76
Q

RNA strcuture?

A
  • folding decides function
  • folding depends on complementary base pairing
  • create stem and loop configurations
  • rna molecule looping in on itself
  • uracil instead of thymine
  • non-standard base pairing can happen (uracil base pairing with guanine) - not possible in DNA
  • modified bases: methylate an adenosine or sum (room for regulation)
77
Q

RNA polymerase

A
  • present in eukaryotes and prokaryotes both
  • DNA dependent (require a DNA template to build the RNA molecule)
  • synthesizes COMPLEMENTARY rna strand
  • addition of 20-50 nucleotides per sec (quick process)
  • addition of new nucleotides - nucleotides added to the 3’ end
78
Q

RNA polymerase direction

A
  • moves along the template strand of DNA in the 3’ to 5’ direction
  • synthesizes a complementary RNA strand in the 5’ to 3’ direction
  • adds nucleotides to the 3’ end of the growing RNA strand (RNA strand elongates in the 5’ to 3’ direction)
79
Q

stages of transcription

A

1) Initiation: RNA polymerase binds to promoter region of DNA sequence, unwinds DNA, begins RNA synthesis

2) Elongation: RNA polymerase moves along DNA synthesizing RNA

3) Termination: RNA polymerase encounters transcription stop signal in DNA

80
Q

operon

A

groups of genes that are transcribed together (prokaryotic) - one initiation step, very long elongation step - just one mRNA molecule for multiple genes

81
Q

prokaryotic transcription

A
  • no physical separation of DNA,
    RNA, ribosomes (all processes take place in cytoplasm)
  • transcription and translation happen together
  • operons: group of genes transcribed together into a single mRNA molecule
  • only one RNA polymerase (core enzyme made up of 5 subunits + sigma factor that binds to promoter = holoenzyme)
  • sigma factor dissociates after 10 Ns (conformation change - becomes a transcriptional elongation complex) - transcription stops with terminator sequence, completed RNA released, may require p factor to dissociate
82
Q

promoter (prokaryote)

A

specific DNA sequence 35 bases upstream of gene

  • Binds transcriptional machinery
  • Location of transcription initiation
  • specific promoter region in bacteria: TTGACA
83
Q

RNA polymerase moves along the DNA template strand in a ____ direction

A

3’ to 5’

84
Q

RNA polymerase 1

A

synthesizes most & larger rRNAs (RNA part of ribosomal structure)

85
Q

RNA polymerase 2

A

synthesizes mRNA + most small nuclear RNAs

86
Q

RNA polymerase 3

A

small RNAs : tRNA + small rRNA

87
Q

primary transcript

A

directly synthesized from the template DNA strand - includes introns (taken out during RNA splicing)

88
Q

tarsncription bubble supercoiling

A
  • positive supercoiling (overwound DNA) in the direction that RNA polymerase is moving
  • behind the RNA polymerase we have underwound DNA (-ve supercoiling)
  • transcription bubble is 15N
89
Q

RNA polymerase

A
  • has magnesium ion to neutralize phosphate of DNA
  • multi-subunit complex
  • RNA transcript exits via channel
  • processive (continually synthesizes)
90
Q

Preinitiation Complex

A
  • RNA polymerase II
  • General transcription factors (GTFs)
  • Promoter
91
Q

TATA box

A

promoter sequence that is 24-32 bases upstream/before initiation site

  • binding site for transcription factors, particularly the TFIID, which facilitates the recruitment of RNA polymerase II to the gene’s promoter
92
Q

promoter sequences

A
  • B recognition element (BRE): even more upstream than TATA (TFIIB)
  • TATA box: 24-32 bases upstream (TBP [tata-binding protein] of TFIID)
  • Initiator (INR): found at the initiation start point (TFIID)
  • Downstream promoter element (DPE): within the gene itself (TFIID)
93
Q

TFIID

A

Subunits:

  • TBP subunit: TATA binding protein; recognizes TATA box
  • TAF subunit: TBP associated factors; regulates DNA binding by TBP - mad eup of multiple polypeptdies (associated factors)

TAF help recognize sequence TBP binds sequence

94
Q

TFIIB

A

positions RNA polymerase at the start site - recognition space for RNAP2

95
Q

TFIIF

A

stabilizes RNA polymerase interaction with TBP and TFIIB - binds directly w RNA polymerase 2

96
Q

TFIIE

A

attracts and regulates TFIIH

97
Q

TFIIH

A

has kinase and helicase activity (unwinds DNA at transcription start point and phosphorylates RNAP2 at the c-terminal so complex can dissociate)

98
Q

capping, polyadenylation, splicing _____

A

happen before export out of nucleus + while RNA is being synthesized enzymes responsible are present on the tail of RNAP2

99
Q

RNA capping

A

Modification of 5’ end with methylated guanine group after 25 nucleotides

100
Q

polyadenylation

A
  • Poly-A tail at 3’ end
  • Encoded in genome
  • 50-250 adenosine

coded in the gene itself (at the end of the gene, there is a DNA template to create this string of adenosine nucleotides) - cap is added, but the polyadenylation is from the DNA template itself

101
Q

capping and polyadenylation purposes

A
  • Translation - play roles in the identification of the mRNA molecule
  • Efficient export
  • Stability
102
Q

split gene

A

has both the coding and noncoding portions

103
Q

difference in size between heterogenous nuclear DNA (hnDNA) and mature mRNA

A

true

104
Q

hnRNA transcripts are processed ______

A

cotranscriptionally

105
Q

why splicing

A

we can create different proteins from taking different combinations of the exons

106
Q

proteins that help cellular RNA polymerases recognize promoters are called

A

transcription factors

107
Q

types of transcription factors

A

regulate gene expression

General TFs: bind at core promoter sites in association with RNA polymerase

Sequence-specific TFs:

  • Bind to various regulatory sites of particular genes
  • Transcriptional activators – stimulate transcription/ expression of a gene
  • Transcriptional repressors – inhibit transcription/ expression of a gene
108
Q

Transcription Factor Structure

A

2 domains:

  • DNA-binding domain: has alpha helix so TF can be inserted into major groove (motif)
  • Activation domain: carries out function

will often dimerize with similar protein (as a form of activation - regulation of gene expression)

109
Q

Oct4

A
  • many transcription factors
  • plays a role in regulating its own transcription
  • TF combination decides extent of transcription
110
Q

embryonic stem cells

A
  • self-renewal
  • pluripotent: can become any other cell
  • turned fibroblasts into stem cells using transcription factors
111
Q

most RNA in cell is _____

A

rRNA (build structure of ribosomes)

112
Q

snoRNA

A

small nucleolar RNAs, help to process and chemically modify rRNA

113
Q

rDNA

A
  • regions of the genome that encode ribosomal RNA (rRNA) - DNA for ribosomal RNA
  • genes organized into multiple tandem repeats (multiple copies of the same gene)
  • rDNA arranged in gene clusters (in the nucleolus?)
114
Q

Eukaryotic Ribosome Structure

A

Ribosome = rRNA + ribosomal proteins

4 distinct rRNAs in eukaryotic ribosome & 2 subunits:

  • Small (40S)– 18 S (+ 33 ribosomal proteins)
  • Large (60S)– 28S, 5.8S, 5S (+ 49 ribosomal proteins)

translational unit: 80S

115
Q

Svedberg unit (S)

A

measure particle’s size based on sedimentation rate - Larger number = larger particle size

116
Q

Prokaryotic Ribosome Structure

A

3 distinct rRNAs in eukaryotic ribosome & 2 subunits:

  • Small (30S)– 16 S
  • Large (50S)– 23S, 5S

translational unit: 70S

117
Q

Synthesis & Processing of Mammalian rRNA Cleavage

A

3 of 4 human rRNAs derived from single primary transcript called the 45S precursor (pre-rRNA) –>. cleavage of primary transcript by nucleases –> mature rRNA

  • 28S, 18S, 5.8S
  • Synthesized by RNA polymerase 1

5S: Synthesized by separate RNA
precursor outside of nucleolus - imported into nucleolus afterwards

  • Via RNA polymerase 3
118
Q

the corresponding segment of DNA from which the primary transcript is transcribed is called a _____

A

transcription unit

119
Q

rRNA Nucleotide Modifications along with cleaving

A
  • Methylation of nucleotides
  • Conversion of uridine (uracil + ribose) –> pseudouridine
  • modifications performed by snoRNPs (small nucleolar ribonucleoprotein particles = snoRNA + proteins)
  • ~200 different snoRNAs – one for every site in the pre-rRNA that is modified
  • conserved in evolution
120
Q

snoRNAs that methylate

A

have Box D (5’-CUGA-3’)

121
Q

snoRNAs that convert uridine to pseudouridine

A

have ACA sequence

122
Q

Synthesis and Processing Eukaryote tRNAs

A
  • genes scattered in small clusters throughout genome rather than tandem repeats
  • RNA polymerase 3
  • primary transcript undergoes modification - trimming of 5’ and 3’ ends
  • Ribonuclease P cleaves at 5’ end
  • Large spacer segments interspersed with tRNA coding sequences
123
Q

why only 20 amino acids if there are 64 codons possible

A

Redundant, Conservative, Unambiguous, Universal

124
Q

Redundant

A

Most amino acids coded by more than one codon

125
Q

Conservative

A

When multiple codons specify same amino acid, the first two bases identical

126
Q

Unambiguous

A

One codon codes for only one amino acid

127
Q

Universal

A

All codons specify same amino
acid across species

128
Q

RNA polymerase movement

A

RNA polymerase moves along the template strand of DNA in the 3’ to 5’ direction, synthesizing a complementary RNA strand in the 5’ to 3’ direction.

  • The template strand of DNA (aka antisense strand) serves as the guide for transcription.
  • RNA is synthesized antiparallel to the template strand.
  • The RNA sequence will be complementary to the template strand and identical (except for uracil replacing thymine) to the coding strand of DNA (also called the sense strand).
129
Q

reading codon

A
  • Codons read in the 5′ to 3′ direction during translation
  • Start codon: AUG (Encodes methionine)
  • Stop codons:
    ▫ UAA
    ▫ UAG
    ▫ UGA
130
Q

anticodon

A

opposite base pair of the codon

131
Q

tRNA

A

Match mRNA codon with amino
acid it codes for

  • Each tRNA is linked to a specific
    amino acid
  • tRNA recognizes a particular
    codon in the mRNA via region
    known as the anticodon
  • 73-93 NTs long
  • D arm recognizes enzyme that attaches its amino acid - aminoacyl tRNA synthetase
  • T arm recognizes ribosome
  • 2 important regions: Anticodon loop (7 NTs) & [AA acceptor arm - 3’ C-C-A sequence]
132
Q

wobble hypothesis

A

explains why multiple codons can code for a single amino acid - Non-Watson-Crick base pairing - Interchangeability of base in 3rd position

133
Q

tRNA charging

A

aminoacyl-tRNA synthetase covalently links amino acids to 3’ end of tRNA (amino acid acceptor arm)

  • enzyme unique to each amino acid
134
Q

what is sometimes needed for the termination of bacterial transcription?

A

rho protein (p factor)

135
Q

small subunit (40S)

A

decodes the genetic message

136
Q

large subunit (60S)

A

catalyzes peptide bond formation

  • contains peptidyl transferase to form peptide bonds
  • tRNA in P site transfers aa to tRNA in A site
137
Q

translation steps

A
  1. Initiation
  2. Elongation
  3. Termination
138
Q

Initiation of Translation in Eukaryotes

A
  • Requires over 12 initiation factors (over 25 polypeptide chains)
  • mRNA binds small & large subunits of ribosome in separate stages
  • 43S complex: small subunit and its initiation factors + (tRNA + GTP + initiation factors)

1) 43S complex + 5’ end of mRNA –> 48S complex (initiation complex; attached to mRNA and searches for AUG)
2) Initiation factors dissociate once initiation complex finds start codon
3) Binding of large ribosomal subunit –> 80S complex

139
Q

Three tRNA binding sites

A
  • A (aminoacyl): Binds incoming aminoacyl-tRNA carrying new aa.
  • P (peptidyl): holds the tRNA with the polypeptide
  • E (exit): holds the tRNA without the aa which is then released by the ribosome
140
Q

Binding 2nd aminoacyl-tRNA to A site requires GTPase

A
  • Bacteria: elongation factor EF-Tu
  • Eukaryotes: eEF1A
141
Q

what enzyme is responsible for covalently linking amino acids to the 3’ end of the cognate tRNA

A

aminoacyl-tRNA synthetase

BMSC 220 post midterm (1 decks)

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