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TH- DNA to Protein Flashcards

1
Q

What is gene expression?

A

process by which DNA directs the synthesis of proteins

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2
Q

What are the 2 stages of gene expression?

A

transcription and translation

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3
Q

What is the one gene-one enzyme hypothesis?

A

one gene dictates the production of one specific enzyme

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4
Q

What is a metabolic pathway?

A

series of chemical reactions occurring within a cell.

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5
Q

what was the one gene-one enzyme changed to and why?

A
  • changed to one gene-one polypeptide

- not all proteins are enzymes and sometimes 2 genes code for a protein

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6
Q

What is transcription?

A

synthesis of RNA using info in DNA

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7
Q

what is mRNA?

A

carries a genetic message from the DNA to the protein-synthesizing machinery of the cell.

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8
Q

What is translation?

A

synthesis of a polypeptide using the information in the mRNA.

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9
Q

What is primary transcript?

A

initial RNA transcript from any gene, including those specifying RNA that is not translated into protein

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10
Q

What is the difference in the flow of genetic info in prokaryotes vs eukaryotes?

A

-prokaryotes don’t have a nuclei so mRNA produced by transcription is immediately translated whereas in eukaryotes the pre-RNA formed has to be processed to mRNA then leave the nucleus for translation to take place

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11
Q

What is a triplet code

A

consists of three, non overlapping, nucleotides.containing genetic instructions for a polypeptide chain.

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12
Q

what are codons

A

mRNA nucleotide triplets

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13
Q

what is the non-template strand often called?

A

coding strand

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14
Q

what are termination codons?

A

codons that don’t code for an amino acid

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15
Q

which is the initiation codon?

A

AUG for Met

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16
Q

what is reading frame and why is it important?

A
  • way of dividing the sequence of nucleotides in a nucleic acid
  • Group the letters incorrectly by starting at the wrong point will cause incorrect result
  • will be made correctly only if the mRNA nucleotides are read from left to right (5’ to 3’) in the groups of three
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17
Q

What are the 3 stages of transcription?

A
  • initiation
  • elongation
  • termination
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18
Q

describe the initiation process of transcription in eukaryotes (4)

A

1- Promoters signal the initiation of RNA synthesis and commonly include a TATA box
2- Several transcription factors, one recognizing the TATA box, must bind to the DNA before RNA polymerase II can bind
3- Additional transcription factors (purple) bind to
the DNA along with RNA polymerase II, forming the transcription initiation complex
4- RNA polymerase II then unwinds the DNA double helix, and RNA synthesis begins at the start point

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19
Q

what is a promoter?

A

describe the initiation process of transcription

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20
Q

what is a terminator?

A

in bacteria, the sequence that signals the end of transcription

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21
Q

what is a TATA box?

A

crucial promoter DNA sequence

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22
Q

what is a transcription unit?

A

stretch of DNA downstream from the promoter that is transcribed into an RNA molecule

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23
Q

describe the elongation process of transcription in eukaryotes (4)

A

1- RNA polymerase II reads the template strand 3’ to 5’ end attaching nucleotides as it goes downstream
2- the pre-mRNA strand is being built 5’ to 3’ as the RNA polymerase keeps adding corresponding bases
3- the adding of the nucleotides elongates the mRNA strand
4- RNA polymerase II zips DNA strands back up as it goes keeping only 10-20 bases exposed

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24
Q

describe the termination process of transcription in eukaryotes (3)

A

1- RNA polymerase II puts a sequence on the DNA called the polyadenylation signal sequence
2- once this stretch of six RNA nucleotides appears, it is immediately bound by certain proteins in the nucleus.
3- 10–35 nucleotides downstream from the AAUAAA, these proteins cut the RNA transcript free from
the polymerase, releasing the pre-mRNA

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25
What are the 2 things that happen in RNA processing?
- Alteration of the ends of mRNA ends | - RNA splicing
26
Describe the 2 modifications that happen during the alteration of the mRNA ends
- The 5' end receives a modified nucleotide 5' cap (modified G) - The 3' end gets a poly-A tail (50 – 250 Adenine nucleotides)
27
What are the 3 functions that these 2 modifications to the mRNA ends share?
- facilitate the export of mRNA from nucleus - help protect the mRNA from breakdown by hydrolytic enzymes - help ribosomes attach to the 5' end of the mRNA once the mRNA reaches the cytoplasm
28
What is RNA splicing?
post transcriptional process in which introns are removed and exons are joined to form mRNA
29
why are introns removed?
because they are the non-coding segments of the pre-mRNA
30
How is pre-mRNA splicing carried out? mention the complex that carries out the process and what it is made up of
- Spliceosomes is a complex that consists of a variety of proteins and several small nuclear ribonucleoproteins (snRNPs) that recognize the splice sites - it binds to several short nucleotide sequences along an intron - intron is then released and the complex join the exons together - small RNAs also catalyze this reaction
31
what are ribozymes?
RNA molecules that function as enzymes
32
What are the 3 properties of RNA that enable it to function as an enzyme?
- It can form a three-dimensional structure because of its ability to base pair with itself - Some bases in RNA contain functional groups - RNA may hydrogen-bond with other nucleic acid molecules
33
what is alternative RNA splicing?
Many genes give rise to two or more different polypeptides, depending on which segments are treated as exons during RNA processing
34
What is domain?
A specific physical region or amino acid sequence in a protein which is associated with a particular function or corresponding segment of DNA.
35
what is exon shuffling and what does it do?
- molecular mechanism for the formation of new genes. - a process through which two or more exons from different genes can be brought together , or the same exon can be duplicated, to create a new exon-intron structure.
36
What is tRNA?
it is a translator of the codon message along the mRNA
37
Describe the structure of a tRNA?
- carries a specific amino acid on one end | - an anticodon on the other end; the anticodon base-pairs with a complementary codon on mRNA
38
What is an anticodon?
particular nucleotide triplet that base-pairs to a specific mRNA codon. written 3' to 5'
39
Which enzyme is the correct matching up of tRNA and amino acid is carried out by?
aminoacyl-tRNA synthetase
40
Describe the process of Linkage of a tRNA to its amino acid (3)
1- amino acid and the appropriate tRNA enter the active site 2- Using ATP, the synthetase catalyzes the covalent bonding of the amino acid to its specific tRNA 3- tRNA with amino acid is released by the synthetase
41
What is wobble and which bases are capable of it?
- it is flexible base pairing at the 3' position of the codon and 5' of the tRNA - only G,U, and I are capable of 5' wobble
42
what is the difference between eukaryotic and bacterial ribosomes?
eukaryotic ribosomes are slightly larger, as well as differing somewhat from bacterial ribosomes in their molecular composition
43
Describe the 3 binding sites for tRNA on a ribosome
- P site holds the tRNA that carries the growing polypeptide chain - A site holds the tRNA that carries the next amino acid to be added to the chain - E site is the exit site, where discharged tRNAs leave the ribosome
44
state the names of the 3 binding sites
- P= peptidyl tRNA binding site - A= aminoacyl-tRNA binding site - E= exit site
45
Describe the initiation process of translation (4)
1-start codon (AUG) signals the start of translation 2- small ribosomal subunit binds to both the mRNA and a specific initiator tRNA 3-small subunit moves along the mRNA until it reaches the start codon (AUG) 4-Proteins called initiation factors bring in the large subunit that completes the translation initiation complex
46
What process provides energy for the assembly of the translation initiation complex?
hydrolysis of GTP provides the energy for the assembly
47
Describe the elongation process of translation (5)
1- amino acids are added one by one to the previous amino acid at the C-terminus of the growing chain 2-addition involves several proteins called elongation factors that occur in the 3 step cycle 4- ribosome and the mRNA move relative to each other, unidirectionally 5- mRNA is read from 5' to 3'
48
Describe the 3 step cycle during translation by mentioning their title and what happens in each step
1- Codon recognition. The anticodon of an incoming aminoacyl tRNA base-pairs with the complementary mRNA codon in the A site. Hydrolysis of GTP occurs 2- Peptide bond formation. An rRNA molecule of the large ribosomal subunit catalyzes the formation of a peptide bond between the amino group of the new amino acid in the A site and the carboxyl end of the growing polypeptide in the P site. This removes the polypeptide from the tRNA in the P site and attaches it to the amino acid on the tRNA in the A site. 3-Translocation. The ribosome translocates the tRNA in the A site to the P site. At the same time, the empty tRNA in the P site is moved to the E site, where it is released. The mRNA moves along with its bound tRNAs, bringing the next codon to be translated into the A site.
49
Describe the termination process of translation
1- When a ribosome reaches a stop codon on mRNA, the A site of the ribosome accepts a release factor 2- The release factor promotes hydrolysis of the bond between the tRNA in the P site and the last amino acid of the polypeptide 3- This reaction releases the polypeptide, and the translation assembly then comes apart
50
what is a release factor
a protein shaped like a tRNA, instead of an aminoacyl tRNA
51
What is a signal peptide?
short peptide present at the N-terminus of most newly synthesized proteins that are destined for the endomembrane or secretion system
52
what is signal-recognition particle (SRP)?
recognizes signal peptide and targets the protein to the endoplasmic reticulum in eukaryotes and the plasma membrane in prokaryotes
53
Describe the signal mechanism for targeting proteins to the ER. (6)
1- Polypeptide synthesis begins on a free ribosome in the cytosol. 2- SRP binds to the signal peptide, halting synthesis momentarily. 3- SRP binds to a receptor protein in the ER membrane, part of a protein complex that forms a pore. 4- SRP leaves, and polypeptide synthesis resumes, with simultaneous translocation across the membrane. 5- signal peptide is cleaved (removed) by an enzyme in the receptor 6- rest of the completed polypeptide leaves the ribosome and folds into its final conformation.
54
What is polyribosomes?
more than 1 ribosomes trailing along the mRNA
55
What is a mutation?
changes in the genetic material of a cell or virus
56
what is point mutations?
chemical changes in just one base pair of a gene
57
what are the 2 types of point mutations?
- Nucleotide-pair substitutions | - Nucleotide-pair insertions or deletions
58
what is Nucleotide-pair substitutions?
replacement of one nucleotide and its partner with another pair of nucleotides
59
What is silent mutation?
no observable effect on the phenotype
60
why does Nucleotide-pair substitutions lead to silent mutations?
even if a one base is changed to a different one the entire triplet code still codes for the same amino acid due to the fact that many codons code for the same amino acid
61
What are missense mutations?
Substitutions that change one amino acid to another one
62
What is nonsense mutation and what does it cause?
- changes a codon for an amino acid into a stop codon. | - causes translation to be terminated prematurely
63
what are Nucleotide-pair insertions or deletions?
additions or losses of nucleotide pairs in a gene
64
What is frameshift mutation?
alter the reading frame of the genetic message, the triplet grouping of nucleotides on the mRNA that is read during translation.
65
When does frameshift mutation occur?
whenever the number of nucleotides inserted or deleted is not a multiple of three.
66
What are mutagens?
physical or chemical agents that can cause mutations

Biology (15 decks)

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