DNA and Genetics

Question 1

Describe how mRNA is synthesised at a template strand of DNA.

Answer 1

RNA nucleotides align with complementary bases on DNA. RNA nucleotides join together by RNA polymerase/phosphodiester bonds.

Question 2

Compare and contrast the process of transcription with the process of DNA replication

Answer 2

• both involve the formation of a polynucleotide/phosphodiester bonds
• both involve DNA helicase unzipping the DNA
• transcription uses mRNA nucleotides (AT) replication uses DNA nucleotides (AU).
• transcription uses RNA polymerase, replication uses DNA polymerase.
• transcription only copies template strand of dna/ produces a single strand of mRNA but replication copies both strands of DNA/produces double stranded of DNA.

Question 3

Gene

Answer 3

A section of DNA nucleotides that codes for a specific protein.

Question 4

Where is DNA found?

Answer 4

nucleus of eukaryotic cells

Question 5

Where are proteins made?

Answer 5

ribosomes within the cytoplasm of eukaryotic cells.

Question 6

RNA

Answer 6

ribonucleic acid; single-stranded nucleic acid that contains the pentose sugar ribose. It is a polynucleotide (made up of mononucleotides which contain phosphate groups) and is involved in protein synthesis (making proteins via translation). Contains bases (G,C,A,U (uracil)). There are three versions of it (MRNA,TRNA,rRNA)

Question 7

genetic code

Answer 7

collection of codons of mRNA, each of which directs the incorporation of a particular amino acid into a protein during protein synthesis. (Adenine, uracil, guanine, cytosine).

Question 8

Number of amino combinations

Answer 8

20 (2 bases)

Question 9

Number of triplet combinations

Answer 9

64 (3 bases)

Question 10

Protein synthesis

Answer 10

the formation of proteins by using information contained in DNA and carried by mRNA. (Translation and transcription)

Question 11

Transcription definition

Answer 11

Process by which information on a DNA strand is transferred to an mRNA molecule. Occurs in the nucleus and is controlled by the enzyme RNA polymerase.

Question 12

Transcription process

Answer 12

• occurs in the nucleus
• RNA polymerase binds to the gene being transcribed
  -DNA helicase unzips the double helix and breaks the hydrogen bonds between the base pairs which exposes the part of the gene that will be transcribed.
  -free RNA nucleotides that are complementary to the exposed DNA bases on the template are joined by phosphodiester bonds (forms the phosphate-sugar backbone of the mRNA molecule)
  -once made, the mRNA leaves the nucleus, through the nuclear pores, into the cytoplasm, onto a ribosome.

Question 13

Translation definition

Answer 13

The process of converting mRNA into amino acids that form proteins. Happens in ribosomes in the cytoplasm.

Question 14

Translation process

Answer 14

• amino acids in the cytoplasm are activated for protein synthesis
• ribosomes bind to the mRNA (messenger)
• in the cytoplasm there are free molecules of tRNA (transport) which have a triplet of unpaired bases at one end (anticodon) and a specific amino acid binding site at the other.
• tRNA transfers the amino acid to the ribosome
• the mRNA reads 3 bases at a time as each triplet is read a tRNA delivers the corresponding amino acid, which is added to a chain of amino acids, that once complete folds into a complex shape to form the protein’s secondary, tertiary (and quaternary) structure.

Question 15

Allele

Answer 15

Alternative forms of the gene on the same position (loci) on a chromosome.

Question 16

Phenotype

Answer 16

An organism’s physical appearance, or visible traits.

Question 17

Genotype

Answer 17

genetic makeup of an organism/an organism’s combination of alleles

Question 18

Dominant

Answer 18

Alleles that can be express their phenotypic character with only one example in a body cell.

Question 19

Recessive

Answer 19

Alleles which will be expressed only if homozygous in a body cell and dominant allele not present.

Question 20

Where does translation occur?

Answer 20

ribosome within the cytoplasm

Question 21

Where does transcription occur?

Answer 21

Nucleus

Question 22

What does degenerate mean?

Answer 22

redundant code (codons that encode the same amino acid).

Question 23

Meselson and stahl experiment

Answer 23

Meselson and stahl originally grew DNA in a culture containing N-15 for several generations so that all the bases contained this isotope. They then grew the DNA in a culture of N-14 for one generation. The DNA is then extracted and separated through centrifugation after 1 and 2 (and more) cell cycles. DNA shifts down the diagram from band A to band D throughout the cycles.