2.1 - 2.13 DNA & protein synthesis, genetic code

Question 1

mononucleotides

Answer 1

the building blocks of DNA & RNA, made up of nitrogenous base, phosphate group and pentose sugar

Question 2

nucleic acids

Answer 2

mononucleotides joined together by condensation reaction that produce phosphodiester bond (sugar-phosphate backbone)

Question 3

purines

Answer 3

nitrogenous bases with two nitrogen-containing rings, adenine and guanine

Question 4

pyrimindines

Answer 4

nitrogenous bases with one nitrogen-containing ring, cytosine, uracil, thymine

Question 5

conservative replication

Answer 5

it is the falsified model of DNA replication. the original double helix remains intact and in some way instructs the formation of new identical double helix made uip of entrely new material

Question 6

semiconservative replication

Answer 6

the accepted model of DNA replication. the DNA unzips and new nucleotides align along each strand; each new double helix contains one strand of the orginal DNA and one made up of new material

Question 7

DNA helicase

Answer 7

it is an enzyme that unzips the two strands of DNA by

Question 8

DNA ligase

Answer 8

it is an enzyme that catalyses the formation of phosphodiester bonds between the nucleotides

Question 9

DNA polymerase

Answer 9

it is an enzyme that lines up the new nucleotides along the DNA template strand

Question 10

gene

Answer 10

a sequence of bases on a DNA molecule which codes for a sequence of amino acids in a polypeptide chain that affects a characteristic in a phenotype of the organism

Question 11

codon

Answer 11

a sequence of 3 bases on DNA and RNA

Question 12

anticodon

Answer 12

a sequence of three bases on tRNA that are complementary to the bases in the mRNA codon

Question 13

start codon

Answer 13

a codon that indicates the start of the amino acid chain (AUG), it codes for methionine amino acid

Question 14

stop codon

Answer 14

a codon that indicates the end of the amino acid chain

Question 15

transcription

Answer 15

it is the process by which the DNA sequence is used to make a strand of mRNA in the nucleus

Question 16

where does transcription take place?

Answer 16

it takes place in the nucleus

Question 17

translation

Answer 17

the process by which the DNA code is converted into a protein from the mRNA strand made in the nucleus

Question 18

what makes up ribosomes?

Answer 18

they are made up of RNA molecules and proteins, and consists of one large and one small subunit

Question 19

what does the large subunit of ribosomes do?

Answer 19

it is the binding site for tRNA

Question 20

what does the small subunit of ribosomes do?

Answer 20

it binds to mRNA

Question 21

tRNA

Answer 21

they are small units of RNA that pick up specific amino acids frin the cytoplasm and transport them to the surface of the ribosome to align with mRNA

Question 22

mRNA

Answer 22

they are the RNA formed in the nucleus that carries the genetic code out into the cytoplasm

Question 23

complementary strands

Answer 23

the strands of RNA formed that complements the DNA acting as the coding strand

Question 24

sense strand

Answer 24

carries the genetic code for protein to be produced, it is the same as mRNA except thymine is changed to uracil

Question 25

antisense strand/ template strand

Answer 25

the place where mRNA forms, acts as the the template for an mRNA molecule

Question 26

RNA polymerase

Answer 26

the enzyme that polymerises the nucleotides to form RNA in a sequence determined by the antisense strand of DNA

Question 27

what is the nature of the genetic code?

Answer 27

it is a triplet code that is non-overlapping and degenerate

Question 28

what does non-overlapping code mean?

Answer 28

it means each codon only codes for 1 amino acid with no overlap between codons

Question 29

what does degenerate code mean?

Answer 29

it means different codons can translate for the same amino acid

Question 30

what are the benefits of having a degenrate code?

Answer 30

even if the final base in the triplet is changed, the mutation could still produce the same amino acid and have no effect on the organism

Question 31

what are the benefits of having a non-overlapping code?

Answer 31

a change in a single nucleotide mutation would affect only one amino acid instead of three, if it were overlapping

Question 32

what is point mutation?

Answer 32

it is a change in a single base of the DNA code

Question 33

what is non-coding DNA?

Answer 33

they are DNA that do not code for amino acids

Question 34

why triplet code?

Answer 34

because a triplet code of three bases gives 4x4x4=64 possible combinations which are more than enough for 20 amino acids that are coded for

Question 35

how is DNA replicated?

Answer 35

when DNA replicates, the two strands of the DNA molecule 'unzip' along the line of hydrogen bonds and unravel bythe enzyme DNA helicase. the strands act as templates for the new DNA strands. the exposed bases attract free DNA nucleotides and new hydrogen bonds are formed between matching base pairs. DNA polymerase lines up and catalyses the linking up of the nucleotides along the template strand. DNA ligase catalyses the fomrmation of phosphodiester bonds between the two strands of DNA. the result is two new strands of DNA identical with the original piece. the new molecules automatically coil up into the double helix as weak hydrogen bonds form within the structure.

Question 36

what is the process of Meselson and Stahl's experiment?

Answer 36

DNA from bacteria was grown in a medium containing only 15N, after a few generations, the entire bacterial DNA was made using 15N. the bacteria was then moved to a medium containing only 14N, after 1 round of replication, the bacterial DNA contained 50% 15N & 14N. after a second round of replication, the DNA appeared as 2 bands, one in the hybrid (half 14N half 15N) band position & one in the position of DNA with only 14N.

Question 37

what are the functions of RNA in protein synthesis?

Answer 37

1. it carries the instructions for a polypeptide from the DNA in the nucleus to the ribosomes where proteins are made 2. it picks up specific amino acids form the protoplasm and carries them to the surface of the ribosomes 3. it makes up the bulk of the ribosomes themselves

Question 38

what are the differences between RNA and DNA?

Answer 38

1. it contains a different sugar (ribose vs deoxyribose) 2. it contains a different base (uracil vs thymine) 3. it has a single helix instead of a double helix

Question 38

what are the differences between RNA and DNA?

Answer 38

1. it contains a different sugar (ribose vs deoxyribose) 2. it contains a different base (uracil vs thymine) 3. it has a single helix instead of a double helix

Question 39

what are polysomes?

Answer 39

they are groups of ribosomes, joined by a thread of mRNA that can produce large quantities of a particular protein

Question 40

how is protein synthesised?

Answer 40

the genetic code of the DNA of the nucleus is transcribed onto mRNA. this mRNA moves out of the nucleus into the cytoplasm and becomes attached to a ribosome. molecules of tRNA carry individual amino acids to the surface of the ribosome. the tRNA anticodon lines up beside a complementary codon in the mRNA, held in place by hydrogen bonds, while enzymes link the amino acids together. the tRNA then breaks away and returns to the cytoplasm to pick up another amino acid. the ribosome moves along the molecule of mRNA until it reaches the stop codon at the end, leaving a completed polypeptide chain. the message may be read again and again.

Question 41

how is mRNA made in the nucleus during transcription?

Answer 41

The sense strand of the DNA strand carries the code for the protein to be formed, but the mRNA forms on the antisense strand of the DNA, also called the template strand. it allows the code of the mRNA to reflect the sense code of the DNA. The mRNA which is formed codes for a polypeptide. Part of the DNA unravels and unzips, exposing the bases which act as a template. Beginning at a start codon, which is also the code for methionine. RNA nucleotides align along the exposed sequence of DNA bases in the normal complementary fashion. Then RNA polymerase joins the chain of RNA nucleotides together. The process ends when the chain reaches a stop codon and the mRNA chain separates from the DNA template, allowing the DNA chains of the double helix to re-join.