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Biology Test 5 > Chapter 17 - Protein Synthesis > Flashcards

Chapter 17 - Protein Synthesis Flashcards

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1
Q

Anti

A

= opposite

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2
Q

Exo

A

= out, outside

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3
Q

Intro

A

= within

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4
Q

Muta

A

= change

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5
Q

Gen

A

= producing

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6
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Poly

A

= many

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7
Q

Trans

A

= across

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8
Q

Script

A

= write

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9
Q

5’ Cap

A

the 5’ end of a pre-mRNA molecule modified by the addition of a cap of guanine nucleotide.

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10
Q

A Site

A

One of a ribosomes three binding sites for tRNA during translation.

The A site holds the tRNA carrying the next amino acid to be added to the polypeptide chain.

A stands for aminoacyl tRNA.

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11
Q

Anticodon

A

A specialized base triplet at one end of a tRNA molecule that recognizes a particular complementary codon on an mRNA molecule.

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12
Q

Base-pair Substitution

A

A type of point mutation; the replacement of one nucleotide and its partner in the complementary DNA strand by another pair of nucleotides.

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13
Q

Codon

A

A three-nucleotide sequence of DNA or mRNA that specifies a particular amino acid or termination signal; the basic unit of the genetic code.

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14
Q

Deletion

A

A mutational loss of one of more nucleotide pairs from a gene.

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15
Q

E Site

A

One of a ribosomes 3 binding sites for tRNA during translation.

The E site is the place where discharged tRNAs leave the ribosome

E stands for exit.

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16
Q

Exon

A

A coding region of a eukaryotic gene.

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17
Q

Frameshift Mutation

A

A mutation occurring when the number of nucleotides inserted or deleted is not a multiple of three, resulting in the improper grouping of the following nucleotides into codons.

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18
Q

Insertion

A

A mutation involving the addition of one or more nucleotide pairs to a gene.

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19
Q

Intron

A

A noncoding, intervening sequence within a eukaryotic gene.

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20
Q

Messanger RNA(mRNA)

A

A type of RNA, synthesized from DNA, that attaches to ribosomes in the cytoplasm and specifies the primary structure of a protein.

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21
Q

Missense Mutation

A

The most common type of mutation, a base-pair substitution in which the new codon makes sense in that it still codes for an amino acid.

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22
Q

Mutation

A

A rare change in the DNA of a gene, ultimately creating genetic diversity.

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23
Q

Nonsense Mutation

A

A mutation that changes an amino acid codon to one of the three stop codons, resulting in a shorter and usually nonfunctional protein.

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24
Q

P Site

A

One of a ribosomes thee binding sites for tRNA during translation.

The P site holds the tRNA carrying the growing polypeptide chain.

P stands for peptidyl tRNA.

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25
Q

Point Mutation

A

A change in a gene at a single nucleotide pair.

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26
Q

Poly-A-Tail

A

the modified end of the 3’ end of an mRNA molecule consisting of the addition of some 50 to 250 adenine nucleotides.

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27
Q

Primary Transcript

A

An initial RNA transcript; also called pre-mRNA when transcribed from a protein-coding gene.

28
Q

Promoter

A

A specific nucleotide sequence in DNA that binds RNA polymerase and indicated where to start transcribing RNA.

29
Q

Reading Frame

A

The way a cells mRNA-translating machinery groups the mRNA nucleotides into codons.

30
Q

Ribosomal RNA(rRNA)

A

the most abundant type of RNA, which together with proteins forms the structure of ribosomes.

31
Q

Ribosome

A

A cell organelle constructed in the nucleolus and functioning as the site of protein synthesis in the cytoplasm; consists of rRNA and protein molecules, which make up two subunits.

32
Q

RNA polymerase

A

An enzyme that links together the growing chain of ribonucleotides during transcription.

33
Q

RNA processing

A

Modification of RNA before it leaves the nucleus, a process unique to eukaryotes.

34
Q

RNA splicing

A

The removal of noncoding portions (introns) of the RNA molecule after initial synthesis.

35
Q

TATA box

A

A promoter DNA sequence crucial in forming the transcription initiation complex.

36
Q

Template strand

A

The DNA strand that provides the template for ordering the sequence of nucleotides in an RNA transcript.

37
Q

Transcription factor

A

A regulatory protein that binds to DNA and stimulates transcription of specific genes.

38
Q

Transcription initiation complex

A

The completed assembly of transcription factors and RNA polymerase bound to the promoter

39
Q

Transcription unit

A

A region of a DNA molecule that is transcribed into an RNA molecule.

40
Q

Transfer RNA (tRNA)

A

An RNA molecule that functions as an interpreter between nucleic acid and protein language by picking up specific amino acids and recognizing the appropriate codons in the mRNA.

41
Q

Translation

A

The synthesis of a polypeptide using the genetic information encoded in an mRNA molecule.

42
Q

Triplet code

A

A set of three-nucleotide-long words that specify the amino acids for polypeptide chains.

43
Q

DNA provides inherited genetic information that can be reliably copied and passed between generations

A

o This information is encoded in the sequence of DNA nucleotides

o Individual segments of DNA called genes provide the specific sequences that ultimately instruct the cell through gene expression to manufacture particular RNA or polypeptides

o The strand of DNA used for a given gene is called the template strand
 The template strand’s complementary strand is called the non-template strand
 Which strand is the template strand is dependent on each individual gene

o Base pairs are bracketed in groups of 3 (triplet code) which are called codons
 Codons must be kept in the same reading frame for proper gene expression

44
Q

Gene expression has 2 major steps

A
  1. Transcription: Using a DNA template to provide the pattern to make a messenger, mRNA transcript
  2. Translation: Using the mRNA transcripts to assemble amino acids in the correct order to make a polypeptide
45
Q

Universal Genetic Code

A

o All organisms share the same genetic code of 64 possible unique codons from the 4 nucleotide bases

o 61 of the 64 code for amino acids, 3 are stop codons, one codon (AUG) is the start codon as well as coding for an amino acid

o No codon codes for more than one amino acids but, for a given amino acid, there can be more than one codon that codes for it

46
Q

Promoter region(transcription)

A

The promoter region of a gene is a reliable sequence along the DNA template strand that signals where transcription will begin

o A common promoter region in eukaryotes is the TATA Box

47
Q

RNA Polymerase(Transcription)

A

RNA polymerase is the enzyme responsible for adding RNA nucleotides to the mRNA transcript

o RNA polymerase binds to the promoter region along with several proteins collectively called transcription factors so together they are called the transcription initiation complex

o The section of DNA transcribed is the transcription unit which includes the eventual coding region along with many other additional nucleotides upstream and downstream from the coding region of the gene

48
Q

3 steps of Transcription

A
  1. Initiation: Matching of the transcription initiation complex to the promoter region and separation of the DNA double strands to allow access
  2. Elongation: Adding of RNA nucleotides using the base pairing rules with U substituting for T on the mRNA transcript
    - RNA nucleotides are added to the 3’ end of the transcript
  3. Termination: The mRNA transcript will be released from the DNA template strands at a pre-determined sequence
49
Q

RNA processing(transcription)

A

Eukaryotes make a pre-mRNA transcript during transcription that needs to be edited before translation (Note: Prokaryotes do not have RNA processing and the transcribed mRNA is used immediately)

o The 5’ end of the pre-mRNA receives a 5’ cap (G nucleotide with 3 phosphate groups) and the 3’ end receives a long series of A nucleotides called the poly-A tail
 Both structures serve to protect the mRNA transcript as it moves from the nucleus to the cytoplasm and to help recognition and binding of the mRNA to the ribosomes

o Certain regions in the coding segment called introns are removed from the transcript, leaving segments called exons that will be expressed during translation

50
Q

Ribosomes and Translation

A

Translation occurs at the ribosomes, bound or free

o Ribosomes are made of 2 protein subunits (a large and small) + ribosomal or rRNA molecules

o The initiation of translation occurs when mRNA transcripts attach to the small subunit at the mRNA binding site

51
Q

Amino acids are present in the cytoplasm and enzymes called aminoacyl-tRNA synthases catalyze the attachment of each amino acid to transfer, tRNA molecules(translation)

A

Each tRNA has an amino acid attachment site on one end and a region called the anticodon, which is a triplet of bases complementary to the codon, that matches the amino acid that tRNA holds

52
Q

tRNA’s are matched to the codons along the mRNA transcript(translation)

A

 Initiation of translation begins when the first tRNA (which holds methionine, Met) binds to the start codon AUG on the mRNA

 This first tRNA docks at a specific place on the ribosome called the P site

 Once it has docked, the large subunit joins to the small subunit
• Energy is needed in the form of GTP molecules

 The next tRNA will dock at a site called the A site using its anticodon to match with the next codon on the mRNA

 The first amino acid (Met) will release from its tRNA and move over to the tRNA at the A site, forming a peptide bond with the next amino acid in the sequence
• The start tRNA is now empty and will move to the E or exit site of the ribosome and eventually released back out into the cytoplasm to find another Met molecule

 The tRNA holding the now 2 amino acid long chain will move over to the P site, leaving the A site free for the next tRNA bearing the next amino acid in the chain to join

 GTP molecules are needed to provide the energy for this process

 The polypeptide chain continues to grow until one of the 3 stop codons is reached on the mRNA
• Proteins called release factors bind to the stop codons and this signals the breaking apart of the ribosome subunits, release of the mRNA and completed polypeptide
• The polypeptide chain will undergo modification to form the secondary, tertiary or possibly quaternary structure needed for a functional final protein

53
Q

Mutation

A

A mutation is a change in the DNA nucleotide sequence

o Mutations can be spontaneous mistakes or caused by other agents called mutagens

54
Q

Point Mutation

A

A point mutation is a change in a single base pair

o The base may be substituted, an extra base inserted or one deleted

o More than one base may be affected however in mutations other than point; sometimes whole codons are inserted or deleted

55
Q

Mutations and base substitutions

A

• If a base substitution alters the codon in a way that allows it to still code for the same amino acid as the wild type, the mutation is silent and has no effect on the protein
o This is possible because of the redundancy in the genetic code

• If the base substitution codes for a different codon than the wild type version, it is a missense mutation
o Depending on what amino acid is altered and the location in the polypeptide chain of that amino acid, the result to the protein is variable

• If the base substitution creates a premature stop codon, the protein is more likely to be negatively affected and non-functional, again, dependent on where the mutation occurs in the sequence
o This called a nonsense mutation

56
Q

Mutations and insertions

A

Insertions and deletions of single bases have a far greater potential effect on the protein than substitutions as they will cause a reading frame shift and all remaining codons will be incorrect

o Insertions or deletions of whole codons however may not have a great affect because there will be no reading frame shift, just an extra or missing amino acid which can vary in affect

57
Q

Explain how RNA differs from DNA.

A

Both are nucleic acids so their monomers are nucleotides. RNA nucleotides have a phosphate group like DNA but the 5 carbon sugar is ribose in RNA unlike deoxyribose in DNA. Of the nitrogenous bases, RNA has adenine, cytosine and guanine but thymine is replaced by uracil.
RNA is single stranded while DNA is double stranded. RNA is found in the nucleus but, unlike DNA, is also found outside of the nucleus.

58
Q

explain how information flows from gene to protein

A

The sequence of nucleotides in DNA holds the instructions for making proteins but must first be transcribed into RNA nucleotides. RNA then takes the message out of the nucleus to the ribosomes, the site of protein synthesis. At the ribosomes, RNA is translated into amino acids to form a polypeptide that later folds to become a protein.

59
Q

Distinguish between transcription and translation.

A

Transcription is the copying of DNA nucleotides to RNA nucleotides. Translation is the conversion of RNA nucleotides (codons) into amino acids.

60
Q

Define codon and explain the relationship between the sequence of codons on mRNA and the sequence of amino acids in a polypeptide.

A

A codon is a triplet of nucleotides. With 4 nitrogenous bases, there are 64 different possible codons. Every 3 DNA nucleotides is transcribed into a mRNA codon. Because there are only 20 amino acids, more than one codon can code for a given amino acid but a codon can never be translated into more than one amino acid. There is one codon that translate to the amino acid methionine but is also the Start codon that signals the beginning of the translated region. There are also 3 Stop codons that signal the end of translation. The universal genetic code
designates which codons translate to what amino acids.

61
Q

Explain the significance of the reading frame during translation

A

Is it very important to begin the bracketing of codons at the Start codon and keep the pattern of the next 3 nucleotides designated as the next codon. This is called the proper reading frame. If you shift a nucleotide up or down or otherwise alter the reading frame, you will change the identity of all the subsequent codons which will then translate into entirely different amino acids
possibly.

62
Q

Explain the general process of transcription, including the three major steps of initiation, elongation, and termination.

A

Initiation begins when RNA polymerase binds with a promoter region of DNA and the DNA unwinds. The polymerase begins to add RNA nucleotides that are base paired to the template strand of DNA.

Elongation continues as the polymerase moves downstream, unwinding the DNA as it goes and adding RNA nucleotides in a 5’ to 3’ direction. The DNA will reform the double helix as the RNA polymerase passes.

Termination occurs when the polymerase reaches the terminator sequence and the RNA transcript is released and the polymerase drops off the
DNA.

63
Q

Explain how RNA is modified after transcription in eukaryotic cells.

A

The primary mRNA transcript first gets a 5’ cap and a poly-A tail on the 3’ end which help protect the transcript from degradation as it moves from the nucleus to the ribosome. Regions of nucleotides called introns that will not be used for translation into amino acids are then edited out and the exons or true coding regions are sealed back together.

64
Q

Describe the structure and functions of tRNA

A 
Transfer RNA (tRNA) is the true translator for going between codons and amino acids. There are 45 different tRNA molecules in the cytoplasma. On one end, they have an attachment site for an amino acid. The other end has a special RNA nucleotide sequence called an anticodon that can complementary base pair with the matching codons. There are 64 codons but only 45
anticodons necessary due to the redundancy of the 3rd nucleotide in the codon sequence (a phenomenon called wobble).
65
Q

Describe the structure and function of ribosomes

A

Ribosomes are composed of 2 subunits (one large, one small) made in the nucleus in the special region called the nucleolus. The subunits are made of protein and ribosomal RNA (rRNA). The come out into the cytoplasm and assemble when a mRNA transcript arrives to be
translated. The ribosomes have 3 sites called the A, P and E site. As the mRNA transcript moves through the ribosome, the tRNA carrying the newest amino acid that will be added to the polypeptide stand binds to the A site. The existing polypeptide strand is bound to the P site.
This strand moves over to tRNA that is in the A site as a peptide bond is formed, joining the new amino acid. The tRNA that had contained the polypeptide strand is now discharged from the E site.

66
Q

Describe the process of translation including initiation, elongation, and termination.

A

Initiation brings together the mRNA transcript, the first tRNA carrying the first amino acid of the polypeptide and the 2 subunits of the ribosomes. This establishes the reading frame from this point on.

Elongation continues as new amino acids are added one by one to the growing polypeptide strand as codon matching occurs between the codons on the mRNA and the incoming tRNA molecules.

Termination occurs when one of the 3 Stop codons is encountered and instead of an amino acid, a release factor binds to the Stop codon site and signals the
release of the polypeptide strand.

The ribosomal subunits then break apart.

67
Q

Define point mutations. Distinguish between base-pair substitutions and base-pair insertions.
Define missense and nonsense mutations.

A

A point mutation is a single change in a nucleotide base. With a base pair substitution, the wrong base pair is present but the overall number of base pairs is correct. This change may or may not have a significant effect on the protein made. If the change is in the 3rd base of a
codon, because of redundancy in the genetic code, there will be no change in the amino acid translated and the protein will be the same.

If the change is in the 1st or 2nd spot, the amino acid translated will be different. It depends on the particular protein and where the change occurs if this will greatly affect the protein. This type of change is called a missense mutation when an amino acid is coded for but just not the correct one.

If the change causes a premature Stop codon, this is a nonsense mutation and can have a dramatic effect on the protein. If the change is an insertion of an extra base or the deletion of one, the reading frame will shift from that point on and cause extensive missense or nonsense.

Biology Test 5 (4 decks)

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