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biology 1115 > chapter 16 and 17 > Flashcards

chapter 16 and 17 Flashcards

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1
Q

what does the central dogma of biology describe. how is it important to determine an organism’s phenotype

A

the flow of information in cells. An organism’s phenotype is a product of the proteins it makes

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2
Q

why does genetic code use a triplet codon

A

because a group of 3 bases (codon) code for one particular amino acid

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3
Q

define transcription

A

the process of using a DNA template to make a complementary RNA

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4
Q

define translation

A

the process of using the information in mRNA to synthesize proteins

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5
Q

alleles of the same gene differ in their _____ sequence

A

DNA

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6
Q

the protein produced by different alleles of the same gene frequently differ in their ____ sequence

A

amino acid

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7
Q

what are some exceptions in the central dogma

A

many genes code for RNAs that do not function as mRNAs and are not translated into proteins. These RNAs still perform important functions

Infor flow DNA –> RNA

Sometimes info flows from RNA back to DNA. Some viruses have reverse transcriptase which synthesizes DNA from an RNA template

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8
Q

what happens during transciption

A

one of the 2 DNA strands called the template strand provides a template for ordering the sequence of nucleotides in an RNA transcript

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9
Q

what happens during translation

A

the mRNA base triplets called codons are read in the 5’ to 3’ direction
- each codon specifies the amino acid to be placed at the corresponding position along a polypeptide
-each codon specifies the addition of one of the 20 amino acids

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10
Q

what is genetic code

A

specifies how a sequence of nucleotides code for a sequence of amino acids

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11
Q

what is a group of 3 bases called

A

a codon

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12
Q

what is a triplet code

A

a series of non-overlapping, three nucleotide words

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13
Q

why does a codon have three bases and not more or less

A

DNA only has 4 different letters: A, T, C, and G. But a protein can have 20 different amino acids. This is where codons come in — they help translate the DNA code into a protein code.

The triplet codon is a “sweet spot” that nature landed upon. It’s just enough to cover all the possible amino acids.

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14
Q

how many codons are there and what do they code for

A

there are 64 in total 61 code for amino acids, 1 codes for a start (signals where protein synthesis)

3 are stop codons that signal to end translation

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15
Q

Explain what is meant by the statement, ‘The genetic code is redundant but not ambiguous.’

A

The genetic code is a degenerate code, which means that there is redundancy so that most amino acids are encoded by more than one triplet combination (codon). Although it is a redundant code, it is not an ambiguous code: under normal circumstances, a given codon encodes one and only one amino acid.

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16
Q

how is the genetic code conservative

A

if several codons specify the same amino acid, the first two bases are identical and the third is different

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17
Q

why is the genetic code universal

A

because genes can be transcribed and translated after being transplanted from one species to another

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18
Q

how is the genetic code non overlapping

A

codons are read one at a time

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19
Q

how is the genetic code unambiguous

A

one codon never codes for more than one amino acid

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20
Q

define mutations.
what are the different kinds of mutations

A

a mutation is any permanent change in an organism’s DNA
point mutations resulting from one or a small number of changes. Chromosomal-level mutations are larger in scale

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21
Q

what is a beneficial mutation?

A

increases the fitness of an organism

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22
Q

what is a deleterious mutation

A

decreases the fitness of an organism

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23
Q

most mutations are _____ or _____

A

neutral or deleterious

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24
Q

what is a base pair substitution mutation? what kind of mutation is it?

A

Base-pair substitution mutations occur
when a mistake during DNA synthesis
or DNA repair results in a different
base at a particular location on the
gene

its a point mutation

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25
Q

what are missense mutations

A

when code for a different amino acid

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26
Q

explain the difference between a silent mutation and a missense mutation

give 2 examples of missense mutations

A

missense mutation changes the amino acid sequence, but silent mutations have no effect on the amino acid sequence

siamese cats and Himalayan mice

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27
Q

what are nonsense mutations?

A

nonsense mutations change an amino acid codon into a stop codon

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28
Q

what is a truncated polypeptide? are they functional

A

a polypeptide that is smaller than normal. Nearly all truncated proteins are nonfunctional and unstable

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29
Q

which type of base pair mutatuon is least likely to be harmful? most likely to be harmful?

A

silent mutations are least harmful. Nonsense mutation is most harmful

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30
Q

why are insertion or deletion mutations so harmful

A

they alter the reading frame and produce a frameshift mutation

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31
Q

will a frameshift mutation result in a functional protein

A

no because every other amino acid after point of insertion or deletion will be different

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32
Q

why are chromosomal mutations harmful

A

can change chromosome number or structure

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33
Q

what are the 4 types of different chromosomal mutations

A

inversion: a segment of chromosome breaks off, flips around and rejoins

Translocation: a section of a chromosome breaks off and becomes attached to another chromosome

Deletion: a segment of chromosome is lost

Duplication: a segment of a chromosome is present in multiple copies
-duplication and divergence results in the formation of new genes from duplicated of old ones

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34
Q

define gene family

A

a group of genes with related function

35
Q

list the types of proteins and their functions

A
  1. hemoglobin carries oxygen
    2.enzymes speed up chemical reactions
  2. actin helps with muscle movements
36
Q

what are the 3 structural differences between DNA and RNA

A
  1. RNA is made of ribose sugar DNA is made of deoxyribose
  2. RNA consists of one strand but DNA consists of 2
  3. RNA uses uracil and DNA used thymine
37
Q

How does transcription occur?

A

RNA polymerases synthesize the mRNA version of the instructions stored in DNA
-only one strand of DNA is copied (the template strand)

as a region of DNA unwinds, one strand is used as a template for the RNA transcript to be made
-nucleoside triphosphate (NTPs) are used to produce an RNA transcript that is complementary to the template strand

38
Q

which direction is DNA and RNA read and which direction is it made?

A

read from 3’-5’
synthesized in 5’-3’ direction

39
Q

during transcription which direction is the strand growing in?

A

grows in the 5’-3’ direction

40
Q

what happens during initiation

A

RNA polymerase and associated proteins bind to the DNA duplex at promoter sequence

41
Q

what is the promoter sequence and where are they found

A

sequence that indicate where a gene starts and which DNA strand is the template strand

promoters are located upstream of the transcription start site

42
Q

what bone holds DNA nucleotides together?

What bond holds amino acids together

A

phosphodiester bonds

peptide bonds

43
Q

What is the name of the bond between amino acids? What type of bond is that? What is the name of the reaction that joins two amino?

A

peptide bonds are a type of covalent bonds

dehydration synthesis

44
Q

what happens during elongation?

A

RNA polymerase opens up the DNA double helix, creating a transcription bubble.
The template strand is threaded through RNA polymerase active site

NTPs pair with complementary DNA bases, and polymerization begins

45
Q

how are nucleotides added to the growing RNA polymer

A

RNA polymerase catalyzes the synthesis of phosphodiester bonds

46
Q

What happens during termination? how is it different in prokaryotes and eukaryotes

A

RNA polymerase transcribe a transcription termination signal. In prokaryotes this codes for RNA that forms a hairpin structure. This causes the RNA polymerase to separate from the RNA transcript

In eukaryotes, a poly(A) signal is transcribed rather
than a hairpin, and the RNA downstream is cut.

47
Q

what is the primary transcript and what is it needed for

A

RNA transcript that comes off the template DNA
-it contains information needed to direct the ribosome to produce proteins

48
Q

what is mRNA

A

The RNA molecule that combines with the ribosomes to direct protein synthesis

49
Q

true or false in prokaryotes primary transcript is the mRNA. Why?

A

true because both processes occur in the cytoplasm and the is no nuclear envelope to spatially separate transcription from translation

50
Q

true or false in eukaryotes primary transcript is the mRNA. Why?

A

false because in eukaryotes there’s a barrier (the nuclear membrane) between transcription and translation.

The primary transcript goes through a complex process of chemical modification known as RNA processing

51
Q

what are the 3 types of chemical modifications that occur before the mRNA is translated by the ribosome

A
  1. RNA splicing
  2. addition of a 5’ cap
  3. polyadenylation
52
Q

what happens during RNA splicing

A

one modification of the primary transcript is the excision of a certain sequences known as introns leaving intact the exons
- about 90% of all human genes contain at least one intron

53
Q

why does RNA splicing occur

A

splicing allows different mRNAs and proteins to be produced from one gene
one primary transcript can code for multiple proteins. which protein is formed depends on how the transcript is spliced

54
Q

what is alternative RNA splicing

A

when from slicing which protein is formed depends on how the transcript is spliced

55
Q

what is the 5’ cap that is added to primary RNA transcripts

A

a modified guanine nucleotide that enables ribosomes to bind and protect from degradation

56
Q

what is the 3’ cap that is added to primary RNA transcripts

A

a 100-250 adenine nucleotides that is needed for translation and protects from degradation

57
Q

what is the product after splicing and the addition of a cap and tail

A

a mature mRNA that contains untranslated regions at both ends

58
Q

during transcription what is the template strand

A

provides a template for ordering the sequence of nucleotides in an RNA transcript

59
Q

during translation the mRNA base triplets called ____ are read in the ___ to ___ direction

A

codons

5’ to 3’

each codon specifies which amino acid will be placed at the corresponding position along a polypeptide

60
Q

what happens during translation?

A

in translation, the sequence of bases in an mRNA is decoded to synthesize the amino acid sequence in a protein. Ribosomes catalyze translation of the mRNA sequence into protein
tRNAs bind to amino acids and then transfer them to the growing polypeptide

61
Q

how does translation occur in bacteria vs in eukaryotes

A

in bacteria, ribosomes often begin translating an mRNA before transcription is complete

in eukaryotes transcription and translation are separated. mRNAs are synthesized and processed in the nucleus.
Mature mRNAs are transported to the cytoplasm for translation by ribosomes

62
Q

what is aminoacyl tRNA

A

a tRNA linked to its amino acid

63
Q

describe the structure of tRNA

A

relatively short: 75-85 nucleotides long.

flattened into one plant to reveal its base pairing, a tRNA molecule looks like a cloverleaf.

because of hydrogen bonds, tRNA actually twists and folds into a 3 dimensional molecule

64
Q

what is found at the 3’ end of a tRNA

A

a CCA sequence that is the binding sequence for amino acids

65
Q

what is the bottom loop end of the tRNA

A

forms the anticodon which has a sequence of 3 nucleotides that can base pair with the mRNA codon

66
Q

what is aminoacyl- tRNA synthetases

A

they “charge” the tRNA by catalyzing the addition of amino acids to tRNAs
ATP is needed to attatch tRNA to an amino acid

for each of the 20 amino acids: there is a different aminoacyl tRNA synthetase; there are one or more tRNAs

67
Q

what is the wobble hypothesis

A

there are 61 codons but only about 40 tRNAs in most cells

this is because the anticodon of tRNAs can still bind successfully to a codon whose third position requires a nonstandard base pairing.
one tRNA is able to base pair with more than one type of codon

68
Q

what are the 2 subunits that make up ribosomes?

A

the small subunit holds the mRNA in place

the large subunit is where the peptide bonds form

69
Q

how many tRNAs can line up within the ribosome

A

3

70
Q

what is required for the tRNAs to fit

A

tRNAs can only fit when its anticodon binds to the corresponding codon in the mRNA

71
Q

what are the 3 sites that tRNAs can fir into in the ribosome

A

the A site is the acceptor site for an aminoacyl tRNA

The P site is the peptidyl site where the peptide bond forms

The E site is where tRNAs without amino acids exit the ribosome

72
Q

what is the 3 step sequence that occurs in ribosomes to build a polypeptide

A
  1. an aminoacyl tRNA carrying the correct anticodon for the mRNA codon enters the A site
  2. a peptide bond forms between the amino acid on the A site tRNA and the polypeptide on the P site tRNA
  3. the ribosome moves down the mRNA by one codon and all 3 tRNAs move down one position
    - the tRNA in the E site exits
    -the A site is available for another tRNA to bind

the protein grows by one amino acid with each repeat of the 3 steps

73
Q

amino acids are always added to the ___ end of the poly peptide

A

carboxyl / C- terminous

74
Q

what are the 3 phases of translation

A
  1. initiation
  2. elongation
  3. termination
75
Q

where does the initiation phase of translation begin.
What happens here?

What is this process mediated by?

A

begins near the AUG start codon

The small ribosomal subunit binds to the mRNA at the ribosome binding site

the process is mediated by initiation factors

76
Q

what is the initiator tRNA

A

the first tRNA that carries a modified methylamine

77
Q

what are the 3 steps of translation initiation in bacteria

A
  1. the mRNA binds to a small ribosomal subunit
    2.the initiator tRNA bearing f-met binds to the start codon
  2. the large subunit binds so that the initiator tRNA is in the P site
78
Q

what happens at the start of elongation

A

the initiator tRNA is in the P site; the E and A sites are empty

an aminoacyl tRNA binds to the codon in the A site

the amino acid on the P-site tRNA is connected to the amino acid on the A site tRNA forming a peptide bond

79
Q

what is translocation and what does it accomplish

A

Translocation occurs when the ribosome slides one codon toward the 3’ end of the mRNA
-elongation factors help move the ribosome

  1. the uncharged tRNA from the P site moves to the E site and is ejected from the ribosome
  2. the tRNA attached to the growing protein moves into the P site
  3. opens the A site to expose a new codon which is available to accept a new aminoacyl tRNA
80
Q

dehydration reaction vs hydrolysis

A

dehydration synthesis build molecules and hydrolysis breaks them down and releases energy in the process

81
Q

what happens during termination in the ribosome

A

termination occurs when the A site encounters a stope codon
a protein called a release factor enters the A site

at the end, the newly synthesized polypeptide, tRNAs and ribosomal subunits separate from the mRNA

82
Q

describe release factors? What do they do

A

resemble tRNAs in size and shape, but don’t carry an amino acid.

They hydrolyze the bond linking the P-site tRNA to the polypeptide chain

83
Q

what is the post-translational modifications

A

most proteins go through an extensive series of processing steps called post-translational modification before they are fully functional

folding determines proteins shape and function

84
Q

what are molecular chaperones for

A

to speed protein folding

biology 1115 (4 decks)

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