Molecular basis of biology and evolution

Question 1

What makes DNA ideal for the long-term storage of genetic code data?

Answer 1

It is a durable, double-stranded polymer

Question 2

Describe how the strands are ordered in DNA

Answer 2

With a 3’-OH and a 5’-PO4 on the sugar-phosphate backbone that run in opposite directions on the 2 strands

Question 3

What are the 4 nucleotide bases?

Answer 3

Adenine
Thymine
Guanine
Cytosine

Question 4

What is Watson-Crick base pairing?

Answer 4

A-T

C-G

Question 5

Why must nucleotides be Watson-Crick base-paired?

Answer 5

The double-strand will be disrupted otherwise

Question 6

What are purines?

Answer 6

Heavy nucleotides with 2 rings

A and G

Question 7

What are pyrimidines?

Answer 7

Light nucleotides with 1 ring

T and C

Question 8

Why is one strand from the double-strand always heavier than the other?

Answer 8

Due to different purine/pyrimidine composition

Question 9

Which base pair is stronger?

Answer 9

G and C as they have 3 hydrogen bonds compared to A and T’s 2

Question 10

During DNA replication, which end are new nucleotides added on to?

Answer 10

3’

Question 11

Which direction is DNA replication carried out in?

Answer 11

5’-3’

Question 12

At what speed is DNA elongation in bacteria?

Answer 12

500 bases s^-1

Question 13

At what speed is DNA elongation in vertebrates?

Answer 13

50 bases s^-1

Question 14

What is semi-conservative replication?

Answer 14

The new DNA molecule contains one new strand and one newly synthesised strand

Question 15

What enzyme catalyses the bonding of the nucleotide to the sugar-phosphate backbone?

Answer 15

DNA polymerase

Question 16

What nucleotide replaces thymine during transcription?

Answer 16

Uracil

Question 17

Describe translation?

Answer 17

tRNAs bind specifically to the mRNA and the ribosome catalyses the binding of the amino acid to the polypeptide being synthesised

Question 18

In which direction is the protein-coding segment of a gene written?

Answer 18

5’-3’

Question 19

How are some codons degenerate?

Answer 19

There is some non-specificity in the third codon of the tRNA molecule thus some triplet codons will code for the same amino acid

Question 20

What are some other names for the strand that goes in the 5’-3’ direction?

Answer 20

Plus (+) strand
Coding strand
Sense strand
Non-template strand

Question 21

What are some other names for the strand that goes in the 3’-5’ direction?

Answer 21

Minus (-) strand
Non-coding strand
Antisense strand
Template strand

Question 22

What strand does the forward primer bind to?

Answer 22

The template strand (-) and bases are added in the 5’-3’ direction (downstream)

Question 23

What strand does the reverse primer bind to?

Answer 23

The non-template strand (+) and bases are added in the 5’-3’ direction (upstream)

Question 24

Describe the denaturing step of PCR

Answer 24

Temperature 94-96 degrees Celcius

Weak H bonds between nucleotide bases are broken at high temperatures

Question 25

Describe the annealing step of PCR

Answer 25

45-55 degrees Celcius | Primers anneal

Question 26

Describe the elongation step of PCR

Answer 26

75-80 degrees Celcius | Taq polymerase catalyses the addition of nucleotides to the 3' end of the primers to create a new amplicon (DNA strand)

Question 27

How much of the human genome is made up of protein-coding exons?

Answer 27

~1.5%

Question 28

What are introns?

Answer 28

Originally thought of as junk DNA or remnants of protein domains that had become inactivated or retrovirus that had become inactivated but not eliminated However, the splicosome and snRNAs are involved in splicing out the introns after transcription

Question 29

What are pseudogenes?

Answer 29

Non-functional coding regions where mutations made the gene product inactive or non-functional

Question 30

Why are DNA and amino acid sequences better for phylogenetic construction than morphology?

Answer 30

DNA and amino acid sequences are strictly heritable and are not influenced by the environment or aging and development Molecular characteristics evolve at a more regular rate than morphological characters Allow quantitative statistical analysis There are more molecular characteristics than morphological ones

Question 31

What is the central dogma?

Answer 31

Information flows from DNA to RNA to protein

Question 32

What are the main vehicles for reverse transcriptase activity?

Answer 32

Retrotransposons

Question 33

How do RNA viruses replicate their RNA?

Answer 33

Using RNA dependant RNA polymerase

Question 34

What are RNA dependant RNA polymerases used in eukaryotes for?

Answer 34

Gene silencing, interference, and miRNA replication

Question 35

How does the secondary structure of proteins form?

Answer 35

Spontaneously due to the arrangement of interacting amino acids

Question 36

How do the tertiary and quaternary structures of proteins form?

Answer 36

Through helper proteins such as chaperones in order to fold correctly

Question 37

What are the 2 major types of mutations?

Answer 37

Point and segment

Question 38

Describe point mutations

Answer 38

A single base/base-pair substitution

Question 39

Where do point mutations most commonly occur?

Answer 39

By mispairing during DNA replication

Question 40

What percentage of point mutations cause missense changes to amino acid sequences?

Answer 40

~71%

Question 41

Why is there a higher chance that a synonymous mutation will occur in the 3rd base of a triplet codon?

Answer 41

Due to the degeneracy of the genetic code

Question 42

What is a single nucleotide polymorphism?

Answer 42

A substitution of a single nucleotide at a specific position in the genome that is present in a sufficiently large fraction of the population.

Question 43

What are some diseases that single nucleotide polymorphisms cause?

Answer 43

Sickle-cell anaemia | Cystic fibrosis

Question 44

What are the 3 types of segmental mutations?

Answer 44

Recombination Indel Inversion

Question 45

Describe recombination mutations

Answer 45

Occurs commonly during chromosomal cross-over during meiosis and also during insertion of retroviral sequences where short target sequences are replaced by longer retroviral sequences and retrotransposons

Question 46

Describe indel mutations

Answer 46

Could be either an insertion or a deletion | Are often fatal in coding regions as 2/3 will cause a frameshift mutation

Question 47

Describe unequal crossing over

Answer 47

Results in the deletion of a segment of the DNA in one chromosome (which will likely not survive) and insertion into another

Question 48

Describe inversion mutations

Answer 48

Can occur by intrachromosomal crossing over

Question 49

What base pairs will mutate more rapidly than others>

Answer 49

C and G

Question 50

What are transitions?

Answer 50

Purine:purine and pyrimidine:pyrimidine

Question 51

What are transversions?

Answer 51

Purine:pyrimidine

Question 52

Which out of transitions and transversions are more likely to mutate?

Answer 52

Transitions

Question 53

What is a synonymous mutation?

Answer 53

The evolutionary substitution of one base for another in an exon of a gene coding for a protein, such that the produced amino acid sequence is not modified.

Question 54

What is more likely to occur, missense or synonymous mutations?

Answer 54

Missense

Question 55

What is a missense mutation?

Answer 55

A point mutation in which a single nucleotide change results in a codon that codes for a different amino acid.