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Fall 2023 > BIOL. 1406 Chapter 17 Gene Expression > Flashcards

BIOL. 1406 Chapter 17 Gene Expression Flashcards

1
Q

Gene Expression

A

The process by which DNA directs the synthesis of proteins.
Proteins are the link between genotype and phenotype.
It includes two stages: transcription and translation.

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2
Q

Beadle and Tatum’s Hypothesis

A

One gene - one polypeptide
(multiple polypeptides can form a gene)

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3
Q

RNA

A

Bridge between genes and protein synthesis

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4
Q

Transcription

A

uses a DNA sequence to produce an mRNA

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5
Q

Processing

A

an mRNA undergoes this process before exiting a nuclear envelope;
introns are cut out while exons remain

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6
Q

Translation

A

synthesis of a polypeptide using information from mRNA;
in eukaryotic cells, mRNA processing separates transcription from translation;
in prokaryotic cells, transcription is followed by translation

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7
Q

Ribosomes

A

Sites of translation

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8
Q

Primary Transcript

A

The initial mRNA strand after transcription before processing

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9
Q

Triplet Code

A

a series of non-overlapping three-nucleotide words;
the words of a gene are transcribed into complementary nonoverlapping three-nucleotide words (mRNA);
these words are translated into a chain of amino acids, forming a polypeptide

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10
Q

Template Strand

A

one of the two DNA strands that provides a a sequence of DNA nucleotides for synthesis of complementary mRNA strand;
it is always the same strand for one given gene;
the opposite strand may be a template for a different gene

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11
Q

Codons

A

Triplets of mRNA that are read in the 5’ to 3’ direction during translation ;
each triplet codes for an amino acid in a polypeptide (there are 20 possible amino acids)

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12
Q

Coding Strand

A

A non-template strand that is complementary to the template strand;
contains the same nucleotide sequence (T in DNA is U in RNA)

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13
Q

Number of Possible Codons

A

64 codons;
61 code for amino acids;
3 code for stop signals

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14
Q

Genetic Code

A

64 codons;
redundant (more than one codon may be used to synthesize one amino acid);
not ambiguous (one codon cannot represent more than one amino acid)

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15
Q

Reading Frame

A

Codons must be read in a specific, correct order for a polypeptide to be produced

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16
Q

Evolution of Genetic Code

A

Genetic code is universal; shared by the simplest bacteria and most complex animals.
Genes can be transcribed and translated after being transplanted from one species to the next.
A language that has been operating very early in the history of life.

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17
Q

RNA Polymerase

A

An enzyme that pries apart the two DNA strands and catalyzes the synthesis of an mRNA strand, joining its nucleotides

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18
Q

Stages of transcription

A

1) initiation
2) elongation
3) termination

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19
Q

Initiation

A

After RNA Polymerase II binds to a promoter, the two DNA strands unwind.
The template DNA synthesized in the 3’ to 5’ direction is used to form a complementary mRNA strand (5’ to 3’). At initiation, a small segment of mRNA is visible. Synthesis begins downstream.

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20
Q

Elongation

A

Polymerase begins to move downstream towards the 5’ prime end, unwinding the two DNA strands. After polymerase passes, the strands wind back up. The mRNA strand elongates.

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21
Q

Termination

A

RNA Polymerase II detaches from DNA.
RNA transcript is completed.
DNA strands are rewound.

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22
Q

Promoter

A

the DNA sequence to which RNA polymerase attaches to

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23
Q

Terminator

A

A DNA sequence found in bacteria only that signals the end of transcription

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24
Q

Transcription Unit

A

The stretch of DNA that is transcribed

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25
Q

RNA Polymerase Binding and Initiation of Transcription

A

Promoters signal the transcription start point and usually extend several dozen nucleotide pairs upstream of a start point.
In eukaryotic cells, proteins, transcription factors, guide attachment of RNA Polymerase to DNA strands.
A transcription initiation complex is formed.

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26
Q

Transcription Initiation Complex

A

a completed assembly of RNA Polymerase and transcription factors along a promoter

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27
Q

TATA box

A

a promoter found in eukaryotic cells crucial for forming a transcription initiation complex

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28
Q

Termination of Transcription in Eukaryotic Cells

A

RNA Polymerase transcribes the polyadenylation signal sequence;
RNA transcript is released 10-35 nucleotides past this polyadenylation sequence.

29
Q

RNA Processing

A

Enzymes in a eukaryotic nucleus modify the primary RNA strand (pre-mRNA) before the genetic messages are dispatched to the cytoplasm;
both ends are altered (5’ cap is added on the left ana a poly-A tail is added on the right);
certain interior sections (introns) are cut out, while the remaining parts (exons) are spliced together.

30
Q

Functions of Altered mRNA ends

A

1) export into the cytoplasm
2) protection of mRNA from hydrolytic enzymes
3) attachment of mRNA to ribosomes at 5’ end

31
Q

RNA Splicing

A

Removal of complementary noncoding regions of DNA found in most pre-mRNA transcripts;
these noncoding regions are called introns;
regions that are expressed are called exons;
removal of introns is done by spliceosomes

32
Q

Ribozymes

A

catalytic RNA molecules that function as enzymes and can splice RNA

33
Q

Three properties that allow RNA to function as an enzyme

A
  • it can form a three-dimensional shape due to its ability to base-pair with itself
  • some bases in the RNA contain functional groups that may participate in catalysis
  • RNA may hydrogen bond with other nucleic acids
34
Q

Functional Importance of Introns

A

contain sequences that regulate gene expression and many affect gene products

35
Q

Alternative RNA Splicing

A

Different segments of a gene are treated as exons, allowing a gene to create more than one kind of peptide

36
Q

Protein Domain

A

a region of a protein’s polypeptide chain that is self-stabilizing and that folds independently from the rest

37
Q

Transfer RNA (tRNA)

A

helps a cell translate an mRNA into a protein;
tRNAs transfer amino acids to the growing polypeptide in a ribosome

38
Q

Anticodon

A

A trinucleotide sequence located at one end of a transfer RNA (tRNA) that is complementary to a corresponding to a corresponding codon in a messenger RNA (mRNA)

39
Q

tRNA

A

a single RNA strand that is made up of about 80 nucleotides;
flattened into one plate to reveal its base pairing , a tRNA molecules looks like a cloverleaf;
because of hydrogen bonds, tRNA twists and folds into a three-dimensional shape;
the protruding 3’ end acts as an attachment site for an amino acid

40
Q

Accurate translation required two instances of molecular recognition

A

1) a correct match between a tRNA and an amino acid done by an enzyme, aminoacyl-tRNA synthetase
2) a correct match between a tRNA anticodon and an mRNA codon

41
Q

Wobble

A

Flexible pairing at the third base of a codon;
it allows some tRNAs to bind to more than one codon

42
Q

Aminoacyl-tRNA synthetase

A

enzymes that play a critical role in protein synthesis, pairing tRNAs with their cognate amino acids for decoding mRNAs according to the genetic code

43
Q

Function of Ribosomes

A

Ribosomes facilitate specific coupling of tRNA anticodons with mRNA codons in protein synthesis.

44
Q

Structure of a Ribosome

A

Two structural subunits (large and small) that are made of proteins and ribosomal RNAs (rRNAs);
three binding sites for tRNA:
1) E site - the exit site, where discharged tRNAs leave the ribosome
2) P site - the site that holds the growing peptide chain
3) A site - the site that carries the next amino acid to be added to the chain

45
Q

Three steps of translation

A

1) initiation
2) elongation
3) termination

46
Q

Ribosome Association and Initiation of Translation

A

Initiation of translation starts when the small ribosomal unit binds with the mRNA and a special initiator tRNA;
the initiator tRNA carries the amino acid methionine;
small subunit moves along the mRNA until it reaches the start codon;
initiation factors bring in the large subunit that completes the translation initiation complex

47
Q

Elongation of the Polypeptide Chain

A

During this process, amino acids are added one by one to the C-terminus of the growing chain.
Each addition involves elongation factors.
The process occurs in three steps: codon recognition, peptide bond formation, and translation.
Empty tRNAs released from E site return to the cytoplasm, where they will be reloaded with the appropriate amino acid,

48
Q

Termination of Translation

A

Elongation continues until a stop codon in the mRNA reaches the A site.
The A site accepts a protein called a release factor.
The release factor causes the addition of a water molecule instead of an amino acid.
This reaction releases the polypeptide, and the translation assembly comes apart.

49
Q

mRNA, tRNA, rRNA

A
  1. the manual
  2. carrier of amino acids
  3. the factory
50
Q

Completing and Targeting the Functional Protein

A

The synthesis of the polypeptide chain is not sufficient enough to make a functional protein.
Polypeptide chains are modified or sent to other locations in the cell.

51
Q

Protein Folding and Post-Translational Modifications

A

During synthesis, a polypeptide chain begins to form;
simultaneously, the protein begins to fold into its three-dimensional shape in its secondary or tertiary structure;
A gene determines its primary structure; the primary structure in term determines its shape.
Post-translational modifications may be required before a protein may perform its function.

52
Q

Targeting Polypeptides to Specific Locations

A

Two types of ribosomes in cells: free (cytosol) and bound (ER)
all proteins a synthesized in cytosol;
some move to ER to become a part of endomembrane system
(ribosomes can switch from free to bound)

53
Q

Signal Peptide

A

A sequence of about 20 amino acids at or near the leading end of the polypeptide;
a polypeptide is marked by it when it is bound to move to the ER

54
Q

Signal Recognition Particle (SRP)

A

A particle in a ribosome that recognizes the signal peptide in a protein and escorts it to the ER;
am enzyme removes the signal recognition particle

55
Q

The signal mechanism for targeting proteins to the ER

A

Polypeptide synthesis occurs in the ribosome in the cytosol;
An SRP binds to the signal peptide, halting synthesis momentarily;
The SRP binds to a receptor protein in the ER membrane, part of the protein complex that forms a pore and has signal-cleaving enzyme;
SRP leaves, synthesis resumes, an enzyme cuts off the signal peptide
The rest of the completed protein leaves and folds into itself;
ribosomal components dissociate.

56
Q

Polyribosome (polysome)

A

A complex that is formed by multiple ribosomes, translating a single mRNA

57
Q

Mutations

A

Changes in the genetic makeup of a cell;
if it has an adverse effect on the phenotype of organism, it is considered a genetic disorder or a hereditary disease.

58
Q

Point Mutations

A

Changes in just one nucleotide base pair of a gene;
the change of a single nucleotide in a DNA strand can lead to a production of an abnormal protein;
two types: single nucleotide-pair substitutions and nucleotide-pair insertions or deletions

59
Q

Nucleotide-Pair Substitution

A

Process that replaces one nucleotide and its partner with another pair of nucleotides

60
Q

Silent Mutation

A

A substitution that has no effect on the amino acid formation because of the redundancy of the genetic code

61
Q

Missense Mutation

A

A substitution that codes for the amino acid but not the correct amino acid

62
Q

Nonsense Mutation

A

A substitution that changes an amino acid codon into a stop codon, leading to a non-functional protein

63
Q

Frameshift Mutation

A

Insertions or deletions that shift the reading frame of a gene

64
Q

Mutagens

A

Physical or chemical agents that produce mutations in the genes;
most mutagens are carcinogens, and most carcinogens are mutagens.

65
Q

Carcinogens

A

Cancer-causing chemicals;
not necessarily mutagens

66
Q

Gene Editing

A

Altering genes in a specific way

67
Q

CRISPR-Cas9

A

A powerful technique that is transforming the field of genetic engineering;
in bacteria, the protein Cas9 works together with a guide RNA to help defend bacteria from viruses;
the Cas9 protein will cut any sequence to which it is targeted;
Scientists can introduce this Cas9-guide RNA complex into a cell they wish to alter.

68
Q

CRISPR-Cas9

A

A unique technology that enables geneticists and medical researchers to edit parts of the genome by removing, adding or altering sections of the DNA sequence.

69
Q

Gene

A

A segment of a DNA that codes for production of a protein or an RNA molecule

Fall 2023 (14 decks)

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