CH.3 PPT

Question 1

what is an interrupted gene

Answer 1

gene in which a coding sequence is not continuous due to the presence of introns

Question 2

what is an exon

Answer 2

sequence of a gene that encode the mature RNA product (protein “coding” sequences)

Question 3

what is an intron

Answer 3

a segment of DNA that is transcribed, but later removed from within the transcript by splicing together the sequences (exons) on either side of it

Question 4

what is RNA splicing

Answer 4

process of excising introns from RNA and connecting the exons into a continuous mRNA

Question 5

what is primary (RNA) transcript

Answer 5

the original unmodified RNA product corresponding to a transcription unit

Question 6

what is a mature transcript

Answer 6

a modified RNA transcript. modification may include alterations to the 5’ and 3’ ends and removal of introns

Question 7

what does each mature mRNA consist of

Answer 7

untranslated 5’ region (5’ UTR), a coding region, and an untranslated 3’ UTR

Question 8

what can mutations in introns affect

Answer 8

RNA processing and hence may influence the sequence and/or production of a polypeptide

Question 9

a mature transcript contains all of the following except
a. 5’ UTR
b. introns
c. exons
d. 3’ UTR

Answer 9

b. introns

Question 10

what is negative selection (* slide)

Answer 10

the lack of selective pressure to produce a functional polypeptide (there is no pressure to keep that gene functional b/c there is another functional copy)

Question 11

what occurs in negative selection in terms of introns and exons evolving

Answer 11

introns evolve much more rapidly than exons because of the lack of selective pressure to produce a polypeptide with a useful sequence

Question 12

what is a positive selection (* slide)

Answer 12

when an individual with an advantageous mutation survives (is able to produce more fertile progeny; drug resistance bacteria relative to others without the mutation)

Question 13

what occurs in positive selection in terms of introns and axons evolving

Answer 13

introns evolve more slowly than exons (because we want to maintain advantageous mutations)

Question 14

iCLICKER: due to negative selection
a. introns usually evolve more slowly than axons do

b. exon size tends to increase over evolutionary time

c. exons usually evolve more slowly than introns do

d. the number of exons tends to decrease over evolutionary time

e. introns and exons usually evolve at about the same rate

Answer 14

c. exons usually evolve more slowly than introns do

Question 15

most genes are ______ (don’t have introns) in ______ and _____ but are _______ (do have introns) in ______ eukaryotes

Answer 15

most genes are uninterrupted (don’t have introns) in yeast and bacteria but are interrupted (do have introns) in multicellular eukaryotes

Question 16

the overall length of a gene is determined largely by what

Answer 16

introns

Question 17

introns are ____ in unicellular/oligocellular eukaryotes but can be ____ in multicellular in eukaryotes

Answer 17

short = unicellular/oligocellular
long = multicellular

Question 18

in multicellular eukaryotes, what primarily accounts for the variety in gene sizes?

a. exons are large and are highly variable in their size

b. exon size tends to increase over evolutionary time

c. exons are small, so if a gene has a lot of exons, it will be much larger than a gene with fewer exons

d. the number and size of introns varies greatly across genes

e. the number of introns increases over evolution, but all introns generally remain small

Answer 18

d. the number and size of introns varies greatly across genes

Question 19

what is translation

Answer 19

process by which a protein is synthesized from the information contained in a molecule of messenger RNA (mRNA)

Question 20

how is the genetic code read

Answer 20

read in triplet nucleotides called codons

Question 21

each codon codes for…

Answer 21

an amino acid

Question 22

codons are _______ and read from a ____ starting point

Answer 22

codons are non overlapping and read from a fixed starting point

Question 23

what is an open reading frame (ORF)

Answer 23

sequence of DNA consisting of triplets that can be translated into amino acids starting with an initiation codon and ending with a termination codon

Question 24

what is the use of alternative initiation or termination codons mechanism (* slide)

Answer 24

it allows multiple variants of a polypeptide chain

Question 25

what is an overlapping gene (* slide)

Answer 25

a gene in which part of the sequence is found within part of the sequence of another gene

Question 26

what occurs in an overlapping gene mechanism (* slide)

Answer 26

where different polypeptides can be produced from the same sequence of DNA when the mRNA is read in different reading frames (as two overlapping genes) (viral and mitochondrial genes)

Question 27

what is a nested gene (* slide)

Answer 27

a gene that may be found in the intron of a host gene, often on the opposite strand

Question 28

what is alternative splicing (* slide)

Answer 28

the inclusion or exclusion of specific exons within a gene. it produces polypeptides that differ be the presence/absence of certain regions

Question 29

majority of human genes are

Answer 29

alternatively spliced

Question 30

iCLICKER: in many multicellular eukaryotic genes, different polypeptides can be produced from the same stretch of DNA duplex primarily due to

a. genes found within the introns of a larger gene

b. alternative splicing of the mRNA transcript

c. extensive somatic recombination in individual cells

d. multiple open reading frames in the same sequence

e. different genes on the two complementary strands

Answer 30

b. alternative splicing of the mRNA transcript

Question 31

what is a gene family

Answer 31

a set of genes within a genome that encodes related or identical proteins or RNAs (most often the members are related but not identical)

Question 32

what is a superfamily

Answer 32

a set of genes all related, presumably descended from a common ancestor, but now showing considerable variation

Question 33

a set of homologous genes (homologs) should share what

Answer 33

common features that preceded their evolutionary separation

Question 34

what is a homologous gene (homolog) (* slide)

Answer 34

gene inherited in two species by a common ancestor

Question 35

what is orthologous genes (* slide)

Answer 35

genes in different species that originated by descent from a common ancestor

Question 36

what is paralogous sequences? (* slide)

Answer 36

sequences generated by a gene duplication event (either before or after speciation). they typically have the same or similar function

Question 37

what is an in-paralogs

Answer 37

arise after a speciation event

Question 38

what is an out-paralogs

Answer 38

arise before a speciation event

Question 39

iCLICKER: what event creates paralogous genes

a. the independent need for a trait with a specific function in two different species

b. a gene duplication followed by a gene mutation within a species

c. evolution of a new species from another one

d. pure dumb luck

Answer 39

b. a gene duplication followed by a gene mutation within a species

Question 40

alternative splicing can take the form of…

Answer 40

including or excluding individual exons or choosing between alternative exons

Question 41

the genetic code is ____ or ____

Answer 41

degenerate or redundant