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Biology > TH- DNA to Protein > Flashcards

TH- DNA to Protein Flashcards

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AP® Biology flashcards Biology 101 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
Q

What are the 2 things that happen in RNA processing?

A
  • Alteration of the ends of mRNA ends

- RNA splicing

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26
Q

Describe the 2 modifications that happen during the alteration of the mRNA ends

A
  • The 5’ end receives a modified nucleotide 5’ cap (modified G)
  • The 3’ end gets a poly-A tail (50 – 250 Adenine nucleotides)
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27
Q

What are the 3 functions that these 2 modifications to the mRNA ends share?

A
  • 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
Q

What is RNA splicing?

A

post transcriptional process in which introns are removed and exons are joined to form mRNA

29
Q

why are introns removed?

A

because they are the non-coding segments of the pre-mRNA

30
Q

How is pre-mRNA splicing carried out? mention the complex that carries out the process and what it is made up of

A
  • 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
Q

what are ribozymes?

A

RNA molecules that function as enzymes

32
Q

What are the 3 properties of RNA that enable it to function as an enzyme?

A
  • 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
Q

what is alternative RNA splicing?

A

Many genes give rise to two or more different polypeptides, depending on which segments are treated as exons during RNA processing

34
Q

What is domain?

A

A specific physical region or amino acid sequence in a protein which is associated with a particular function or corresponding segment of DNA.

35
Q

what is exon shuffling and what does it do?

A
  • 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
Q

What is tRNA?

A

it is a translator of the codon message along the mRNA

37
Q

Describe the structure of a tRNA?

A
  • 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
Q

What is an anticodon?

A

particular nucleotide triplet that base-pairs to a specific mRNA codon. written 3’ to 5’

39
Q

Which enzyme is the correct matching up of tRNA and amino acid is carried out by?

A

aminoacyl-tRNA synthetase

40
Q

Describe the process of Linkage of a tRNA to its amino acid (3)

A

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
Q

What is wobble and which bases are capable of it?

A
  • 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
Q

what is the difference between eukaryotic and bacterial ribosomes?

A

eukaryotic ribosomes are slightly larger, as well as differing somewhat from bacterial ribosomes in their molecular composition

43
Q

Describe the 3 binding sites for tRNA on a ribosome

A
  • 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
Q

state the names of the 3 binding sites

A
  • P= peptidyl tRNA binding site
  • A= aminoacyl-tRNA binding site
  • E= exit site
45
Q

Describe the initiation process of translation (4)

A

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
Q

What process provides energy for the assembly of the translation initiation complex?

A

hydrolysis of GTP provides the energy for the assembly

47
Q

Describe the elongation process of translation (5)

A

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
Q

Describe the 3 step cycle during translation by mentioning their title and what happens in each step

A

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
Q

Describe the termination process of translation

A

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
Q

what is a release factor

A

a protein shaped like a tRNA, instead of an aminoacyl tRNA

51
Q

What is a signal peptide?

A

short peptide present at the N-terminus of most newly synthesized proteins that are destined for the endomembrane or secretion system

52
Q

what is signal-recognition particle (SRP)?

A

recognizes signal peptide and targets the protein to the endoplasmic reticulum in eukaryotes and the plasma membrane in prokaryotes

53
Q

Describe the signal mechanism for targeting proteins to the ER. (6)

A

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
Q

What is polyribosomes?

A

more than 1 ribosomes trailing along the mRNA

55
Q

What is a mutation?

A

changes in the genetic material of a cell or virus

56
Q

what is point mutations?

A

chemical changes in just one base pair of a gene

57
Q

what are the 2 types of point mutations?

A
  • Nucleotide-pair substitutions

- Nucleotide-pair insertions or deletions

58
Q

what is Nucleotide-pair substitutions?

A

replacement of one nucleotide and its partner with another pair of nucleotides

59
Q

What is silent mutation?

A

no observable effect on the phenotype

60
Q

why does Nucleotide-pair substitutions lead to silent mutations?

A

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
Q

What are missense mutations?

A

Substitutions that change one amino acid to another one

62
Q

What is nonsense mutation and what does it cause?

A
  • changes a codon for an amino acid into a stop codon.

- causes translation to be terminated prematurely

63
Q

what are Nucleotide-pair insertions or deletions?

A

additions or losses of nucleotide pairs in a gene

64
Q

What is frameshift mutation?

A

alter the reading frame of the genetic message, the triplet grouping of nucleotides on the mRNA that is read during translation.

65
Q

When does frameshift mutation occur?

A

whenever the number of nucleotides inserted or deleted is not a multiple of three.

66
Q

What are mutagens?

A

physical or chemical agents that can cause mutations

Biology (15 decks)

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