Molecular genetics - Test

Question 1

Which nitrogenous bases are purines? What is their structure?

Answer 1

Adenine and guanine. They are double ringed structures.

Question 2

Which bases are pyrimidines? What is their structure?

Answer 2

Thymine, cytosine and uracil in RNA. They are single ringed structures

Question 3

What is Chargaff’s rule?

Answer 3

That the percent composition of a purine, is the same as its pyrimidine counterpart.

Question 4

What are the purine-pyrimidine combos?

Answer 4

A-T or U and G-C

Question 5

Initiation (DNA)

Answer 5

DNA unzips into the leading strand and the lagging strand. Helicase facilitates it, and SSBPs stabilize the DNA

Question 6

What is elongation

Answer 6

The leading and lagging strands are synthesized. DNA polymerase III synthesizes the leading strand, DNA polymerase I synthesizes the lagging strand with the help of primase.

Question 7

What is termination?

Answer 7

The two new DNA molecules wind into their helices. The replication machine is disassembled, and DNA polymerase II proofreads the sequencing

Question 8

messenger RNA (mRNA)

Answer 8

RNA synthesized from the DNA of genes. It contains the genetic information for protein synthesis and carries it to the protein synthesis machinery. It determines the amino acid sequence of a protein.

Question 9

Triplet hypothesis

Answer 9

Hypothesis stating that the genetic code is read three nucleotide bases at a time

Question 10

What is the start amino acid? What is its codon?

Answer 10

Methionine. Its codon is AUG

Question 11

What are the stop codons?

Answer 11

UGA, UAA, UAG

Question 12

What are the steps to protein synthesis?

Answer 12

Transcription and Translation

Question 13

Transcription

Answer 13

The synthesis of RNA from a DNA template.

Question 14

Three differences between RNA and DNA

Answer 14

RNA uses ribose sugar, DNA uses deoxyribose sugar. RNA uses Uracil instead of Thymine. RNA is single stranded, DNA is double stranded.

Question 15

Translation

Answer 15

Synthesis of a protein from an mRNA template

Question 16

Three steps of translation

Answer 16

Initiation, elongation, termination

Question 17

Initiation (transcription)

Answer 17

RNA polymerase binds tightly to a promoter region on DNA. This unzips the DNA into two strands: antisense strand and the sense strand.

Question 18

Antisense strand

Answer 18

The template strand. This one is the strand that RNA polymerase uses to create the mRNA

Question 19

Sense strand

Answer 19

The coding strand. Except for the Thymine, it is identical to the mRNA strand. This strand is useless in protein synthesis.

Question 20

Promoter region

Answer 20

A sequence of nucleotides in DNA that tells RNA polymerase where to bind and in what orientation

Question 21

Elongation (transcripton)

Answer 21

RNA polymerase complex works along the DNA molecule to make the mRNA strand. It also works in the 5’ to 3’ direction. As soon as the RNA polymerase starts to move, another polymerase can bind and make another mRNA strand. Hundreds can be made from one gene at the same time. No proofreading

Question 22

Termination (transcription)

Answer 22

Specific sequences in DNA tells the RNA polymerase where to stop. RNA polymerase detaches and the DNA double helix reforms. This is precursor mRNA or primary transcript

Question 23

pre-mRNA (primary transcript)

Answer 23

unprocessed mRNA

Question 24

mRNA processing

Answer 24

Eukaryotes only. A 5’ cap is added, which is a modified G nucleotide. Added to the 5’ end. This is what makes it recognizable to the protein synthesis machine. A 3’ poly-A tail is added. This is a string of about 200 A’s that makes the strand more stable and able to last in the cytoplasm.

Question 25

Introns

Answer 25

Non-coding regions. Removed.

Question 26

Exons

Answer 26

Coding regions. When Introns are removed, these are joined together to make mature mRNA

Question 27

snRNPs and snRNA

Answer 27

Bind to the places where Introns and Exons meet. snRNPs interact with other proteins to make large splicesome complexes and remove introns. Many exons may be used and this allows more proteins to be made from a single gene.

Question 28

tRNA

Answer 28

Contains an anticodon that complements the mRNA. It has the corresponding amino acid attached to it. Cloverleaf shape. Formed by anticodon group, acceptor stem and aminoacyl.

Question 29

Ribosomes

Answer 29

Made of rRNA and involved in protein synthesis. They are structures that allow a place for the mRNA and tRNAs to interact

Question 30

Translation factors

Answer 30

proteins that act as accessory factors and are needed at every stage

Question 31

anticodon loops

Answer 31

triplet of bases at the bottom end of tRNA. Recognizes and pairs with a codon on mRNA

Question 32

acceptor stem

Answer 32

3' end of tRNA molecule that is the side of attachment for the amino acid. Based on anticodon.

Question 33

aminoacyl-tRNA synthase

Answer 33

attaches the appropriate amino acid to the tRNA. Based on anticodon. One different enzyme for each of the 20 amino acids.

Question 34

How are codons and anticodons written

Answer 34

Codons: 5' to 3' Anticodons: 3' to 5'

Question 35

Polyribosome

Answer 35

Structure when there are multiple ribosomes translating a single strand of mRNA

Question 36

Three steps to translation

Answer 36

Initiation, elongation, termination

Question 37

Initiation (translation)

Answer 37

Small subunit covers 2 codons to ensure the correct reading frame. tRNA's UAC (methionine) bonds to AUG of mRNA. tRNA held in P-site. Larger subunit binds to smaller subunit and A-site is ready to accept another tRNA and amino acid.

Question 38

Large subunit

Answer 38

P-site: Stores the growing protein | A-site: Holds the next tRNA with its amino acid.

Question 39

Large subunit

Answer 39

P-site (peptidly site: Stores the growing protein | A-site (aminoacyl site): Holds the next tRNA with its amino acid.

Question 40

Movement of ribosomes

Answer 40

Moves 5'-3' along the mRNA. 3bases at a time and joins amino acids to each other according to the codons

Question 41

Elongation (translation)

Answer 41

tRNA and it's amino acid enters A-site and pairs to mRNA strand. Peptide bond formed between a.a in P-site and a.a in A-site. Ribosomal unit moves along and releases tRNA without the a.a. Aminoacyl tRNA goes from A-site to P-site. P-site ejects aminoacyl tRNA and A-site can receive more tRNA with a.a

Question 42

Termination (translation)

Answer 42

At stop codons. No tRNA to enter A-site anymore. Protein release factors bind to the stop codon, water molecule added at the end of the chain instead of a.a. Ribosomal subunits separate and peptide chain released. All of this powered by GTP

Question 43

Single-gene mutations

Answer 43

Involve changes to the nucleotide sequence of one gene.

Question 44

Chromosomal mutations

Answer 44

Involve a whole chromosome. May involve multiple genes.

Question 45

Point mutation

Answer 45

Mutation caused by deletion, substitution or addition of a base PAIR. Deletion and addition shifts the whole thing. Substitution may have a very mild effect.

Question 46

Frameshift mutation

Answer 46

When the number of nucleotides added or deleted is not divisible by three, it causes the whole thing to shift and changes the reading frame