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deck_6622634 Flashcards

1
Q

Gene expression-

A

steps in which DNA in the genes code for proteins

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2
Q

Archibald Garrod-

A

studied rare genetic disease called alkaptonuria

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3
Q

alkaptonuria

A

recessive disease in which affected individuals were unable to break down tyrosine, an amino acid. Instead, homogentisic acid accumulates in urine andturns it black. Lacked the enzyme which breaks down homogentisic acid–Mutation in one gene is associated with the absence of this specific enzyme

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4
Q

Beadle and Tatum-

A

studied the fungus Neurospora.

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5
Q

Neurospora Wild Type

A

individual with normal phenotype, which can grownormally on simple growth medium/basic nutrients

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6
Q

Mutant strain (produced by radiation)- Neospora

A

cannot make a substance such as an amino acid, can only grow if that substance is added to growth mediumo Each mutant strain had mutation at only one locus- each gene locus affected only one enzymeCalled this the one-gene, one-enzyme hypothesis

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7
Q

Linus Pauling-

A

Mutation at single locus alters the structure of one polypeptide chain of hemoglobin, causing sickle cell anemiao Therefore- we now conform to the one-gene, one-polypeptide chain hypothesis

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8
Q

Ribonucleic acid, or RNA,

A

link between DNA to protein

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9
Q

Differences between RNA and DNA:

A

o RNA is single strandedo Contains the sugar ribose, not deoxyriboseo Base uracil substitutes for thymine

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10
Q

Transcription-

A

the “copying” of the template strand of DNA and formation of RNA. Forms three types of RNA

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11
Q

three types of RNA

A

mRNA, tRNA, rRNA

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12
Q

Messenger RNA (mRNA)-

A

single, uncoiled strand of RNA that carries information for making a protein

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13
Q

Transfer RNA (tRNA)-

A

single strand of RNA that folds backon itself to form a specific shape. Each tRNA bonds toone type of amino acid and carries it to the ribosome

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14
Q

Ribosomal RNA (rRNA)-

A

globular RNA that is part of the ribosomes of RNA and helps catalyze protein synthesis

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15
Q

Differences between transcription and DNA replication:

A

Only part of the DNA molecule isused as a templateo EnzymeRNA polymerase is used as opposed to DNA polymeraseo Results in one free RNA strand, not a double helixTranscription happens constantly–DNA replication happens during S of cell cycle

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16
Q

Initiation: (transcription)

A

first stage of transcriptiona. RNA polymerase attaches to promoter- region inDNA that is not transcribed, contains the sequenceTATA (TATA box)b. RNA polymerase then unwinds the DNA and initiates transcription

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17
Q

Elongation: (transcription)

A

second stage of transcriptiona. RNA polymerase assembles RNA nucleotides using1 strand of the DNA as a templateb. Occurs in5’ to 3’ direction (new strand is made in 5’ to 3’ directionlike in replication)

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18
Q

Termination: (transcription)

A

third stage of transcriptionRNA polymerase reaches a special sequence ofnucleotides that serve as a termination pointIn eukaryotes- often contains the DNA sequence AAAAAAARNA polymerase releases the DNA template and the new RNA strand

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19
Q

In eukaryotic cells, each new molecule of mRNA is only what? what does this necessitate?

A

“pre-mRNA”- must be modified before it can code for proteins

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20
Q

Modification of mRNA–5’ end

A

A modified GTP (guanosine triphosphate- or a guanine nucleotide with two extra phosphate groups) is added to the 5’ end to form a 5’ cap. Provides stability to new mRNA and a point of attachment for the ribosome.

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21
Q

Modification of mRNA–3’ end

A

3’ end of mRNA- 150 – 200 adenine nucleotides are added- poly-Atail (-A-A-A….A-A-3’)o Provides stabilityo Controls movement of mRNA across the nuclear envelope

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22
Q

heterogenous nuclear RNA,

A

Pre-mRNA

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23
Q

Alternative splicing-

A

Different exons can be kept in or snippedout- will change the types of proteins that are produced. Explains how human cells can make hundreds ofthousands of proteins from only about 20k genes

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24
Q

Exons-

A

sequences that express a code for a polypeptide. exported from nucleus.

25
Q

Introns-

A

intervening base sequences that must be removed before translation–stay in the nucleus

26
Q

Small nuclear ribonucleoproteins, or snRNPs,

A

delete out the introns and splice the exons

27
Q

Translation-

A

information found in mRNA is used to specify the amino acid sequence ofa polypeptide

28
Q

codons

A

The mRNA is read as codons- sequences of three consecutive bases of mRNA which specifies one amino acid

29
Q

codon code

A

Code is called triplet code because each codon consists of three nucleotides. All of the codons collectively form the genetic code

30
Q

cracking of genetic code

A

By 1967, the genetic code was “cracked”- scientists hadidentified the amino acids for all 64 possible codons. The genetic code is universal- the same codons code for the same amino acids in all organisms. Since there are 64 possible codons and only 20 amino acids,more than one codon specify certain amino acids

31
Q

anticodon

A

A particular tRNA can recognize a specific codon because it has a sequence of three bases, called the anticodon, that is complementary to the mRNA codon, forming hydrogen bonds with one another.

32
Q

Wobble effect-

A

The codon- anticodon interactions are not as strong for the third base in a codon

33
Q

Stop codons

A

UAA, UAG, UGA

34
Q

start codons

A

AUG

35
Q

effect of binding of anticodon

A

The amino acids carried by the tRNA can then be linkedtogether by peptide bonds in the order specified by the sequence of codons in the mRNA.

36
Q

Ribosomes

A

the site of translationConsist of two subunits, small and largeEach is made of proteins and rRNADuring translation, the mRNA molecule fits between the two subunitsContain 2 binding sites for tRNA: P, A, (and E)

37
Q

Translation

A

mRNA moves out of nucleus to the cytoplasm. Requires the coordinated functioning of protein and RNA components of the ribosomes, mRNA, and amino acids linked to tRNAs.

38
Q

tRNA action translation

A

Folds on itself to form three or more loops of unpaired nucleotidesBottom loop contains an anticodon- 3 bases at bottom of molecule that will complementary base pair with thecodon found on the mRNAEach kind of tRNA binds to a specific type of amino acid at the three prime top of the moleculeSEE DIAGRAM

39
Q

P site-

A

peptidyl site-tRNA holding growing polypeptide chain binds here

40
Q

A site-

A

aminoacyl site- tRNA delivering the next amino acid in the sequence binds here

41
Q

E site-

A

Exit site–tRNA exits here after dropping off its amino acid

42
Q

Initiation-SEE DIAGRAM

A

first stage of translation:The small ribosomal unit binds to the five prime end of the mRNAAn initiator tRNA binds to an mRNA at the startsequence AUG. The initiator tRNA carries with it theamino acid met The large ribosomal unit binds to the small unit. Theinitiator tRNA occupies the P site

43
Q

initiation complex

A

ribosome + mRNA + tRNA

44
Q

Elongation-SEE DIAGRAM (translation)

A

second stage of translation:
a. A new tRNA bearing an amino acid binds to the A site of the ribosome.
b. Methionine is removed from the first tRNA andattaches to the amino acid on the newly arrived tRNA
That first tRNA is then released into the cytoplasmwhere it can once again bind to its amino acid. Meanwhile, the second tRNA can now move from the A site into the vacated P site.
The A site is now open, exposing the next codon. A new tRNA carrying a new amino acid enters the A site.( The two amino acids in the P site bind to this new amino acid, forming a chain of 3 amino acids. This continues over and over, and the chain elongates by one amino acid at a time- dictated by the codons in the mRNA.)

45
Q

Termination-SEE DIAGRAM

A

Ribosome encounters a “stop” codon. No tRNA molecule bindsInstead, a release factor (special protein) binds to A siteTherefore, when the tRNA in the P site separates fromthe amino acid, the newly synthesized polypeptide chain is free

46
Q

What happens after translation has completed?

A

amino acids of the polypeptide chain can associate to form secondary and tertiary structures

47
Q

polysomes-

A

clusters of many ribosomes translating an mRNA transcript at the same time. found in bacterial cells that rapidly use or secrete proteins.

48
Q

Mutation-

A

change in the nucleotide sequence of DNA. not every mutation causes an observable change (some codons code for same amino acids, change in eye color in an skin cell). Mutations provide diversity

49
Q

Base substitution-

A

change in only one pair of nucleotides

50
Q

Missense mutations-

A

Base substitution. replacement of one amino acid by anotherCan alter active site of enzymes

51
Q

silent mutation-

A

Base substitution. codes for the same amino acid/no observable change

52
Q

Nonsense mutations-

A

Base substitution. convert a code for an amino acid into a stop codon correct protein can’t be produced

53
Q

Frame shift mutation-

A

one or two nucleotide pairs are inserted ordeleted from the molecule, altering the reading frame (sometimes more –not multiples of 3) Codons downstream from this mutation specify a new sequence of amino acids resulting in a new polypeptide chain

54
Q

Transposons, or transposable genetic elements-

A

DNA sequences that jump from one area into the middle of a geneCan alter the timing of the gene or block its activityDiscovered by Barbara McClintock- noticed that certain genes in corn would spontaneously turn on or offTransposons require an enzyme transposase for incorporation into a new locationMost are retrotransposons

55
Q

retrotransposons

A

form copies of itself by producing an RNA intermediate, then an enzyme called reverse transcriptase forms DNA from that RNA and the DNA jumps into a gene

56
Q

Causes of Mutations

A

Spontaneous or mutagens

57
Q

Spontaneous mutations

A

Mistakes inDNA replication• Defects inmitotic or meiotic separation• Hot spots

58
Q

Hot spots-

A

areas of DNA that are more likely than others to mutate–generally areas that have stretches of repeated nucleotides

59
Q

Mutagens-

A

anything that causes a mutation* Radiation• Chemical mutagens can modify bases, leading tomistakes in base pairing- Although mutations in the somatic cells cannot be passed on to offspring,some mutations can lead to cancer. In addition, many mutagens arecarcinogens-agents that can cause cancer

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