week 6 - DNA

Question 1

who discovered that DNA was a double helix

Answer 1

• Watson and Crick

Question 2

what is DNA

Answer 2

• nucleotide polymers arranged as a double helix

Question 3

what are the two strands of nucleotides in DNA held together by?

Answer 3

• base pairing of hydrogen between bases

Question 4

base pairs

Answer 4

• adenine with thymine
• cytosine with guanine

Question 5

DNA is the genetic code that makes us unique

Answer 5

• different arrangements of A, C, G and T lead to different gene sequences
• similar genes may differ between humans and other organisms
• basis of forensic identification using DNA

Question 6

how is DNA replicated?

Answer 6

• replicated during S phase of the cell cycle
• hydrogen bonds are broken
• DNA polymerase replicates DNA
• enzyme adds the nucleotides using the sequence of the parent strand
• end up with the new strand attached to the old

Question 7

DNA erros, mismatches and mutations

Answer 7

• DNA replication has an error rate of about 1 in 10,000 nucleotides
• proofreading by polymerase reduces the error rate to 1 in 10 million nucleotides
• mismatch repair enzymes reduces error rate to 1 in 1 billion nucleotides
• when an error is not repaired = DNA mutation

Question 8

normal gene function depends on DNA repair: the 3 steps

Answer 8

(1) Recognition - damages or mismatched area is detected
(2) removal - the region is removed by enzymes
(3) replacement - DNA polymerase fills in the gap with new nucleotides

Question 9

what causes DNA mutations?

Answer 9

• UV light
• Ionizing radiation
• chemicals (free radicals)

Question 10

Failed DNA repair mechanisms result in disease

Answer 10

• when DNA repair mechanisms fail, diseases such as xeroderma pigmentosum can occur

Question 11

genes encode proteins

Answer 11

• genes code directly for RNA molecules
• RNA molecules are the info to make protein
• a gene is a sequence of DNA that is used to make a copy of an RNA molecule used to make protein
• DNA -> RNA -> Protein

Question 12

messenger RNA

Answer 12

• specifies the order of amino acids in a protein using a series of 3-base codons, where different amino acids are specified by particular codons

Question 13

ribosomal RNA

Answer 13

• as a major component of ribosomes, assists in making the covalent bonds that link amino acids together to make a protein

Question 14

transfer RNA

Answer 14

• transports the correct amino acid to the ribosome, using the information encoded in the mRNA; contains a 3-base anticodon that pairs with a complementary codon revealed in the mRNA

Question 15

RNA

Answer 15

• single stranded
• the base uracil takes the place of thymine
• RNA uses the sugar ribose instead of deoxyribose

Question 16

transcription and translation

Answer 16

• transcription: produces mRNA from the DNA sequence of a gene and then the mRNA moves from the nucleus to the cytoplasm
• translation: assembles the amino acids of proteins using the sequence of the mRNA

Question 17

step one: transcription (DNA to mRNA)

Answer 17

• first thing needed is DNA sequence of a gene
• second thing is RNA polymerase
• transcription begins when RNA polymerase binds to a region of DNA called a promotor

Question 18

step 1: RNA polymerase starts making mRNA

Answer 18

• RNA polymerase begins to unwind the DNA
• then it starts adding and linking nucleotides complementary to one of the DNA strands

Question 19

how is transcription different from DNA replication?

Answer 19

• only one strand of DNA is used as a template in transcription
• product is single stranded RNA, not double stranded DNA
• specific segments (genes) are transcribed into RNA not the entire DNA molecule
• happens all the time
• DNA is only replicated prior to cell division

Question 20

step 2: translation (mRNA to proteins)

Answer 20

• genes are segments of DNA that encode proteins
• made into mRNA
• mRNA is the info that specifies the order of amino acids
• sequence of 3 nucleotides in mRNA specifies an amino acid
• each group of 3 nucleotides is called a codon

Question 21

genetic code for amino acids: 3 important points

Answer 21

• more than one code for an amino acid
• starting point for mRNA translation is AUG
• end point for mRNA translation is the stop codon (UAA, UAG, UGA)

Question 22

4 things needed for construction of protein

Answer 22

• mRNA molecule
• ribosomes: made up of rRNA and proteins (it reads to the mRNA sequence and links the amino acid)
• amino acids
• tRNA: will bring the amino acids to the mRNA and ribosomes

Question 23

tRNA molecule

Answer 23

• RNA molecule folded on itself
• contains a sequence called an anticodon
• each tRNA carries the specific amino acid that is called for by the codon on the mRNA

Question 24

how does the mRNA, ribosome and tRNA work together?

Answer 24

• ribosome moves down the mRNA until it reaches the start codon
• calls for the tRNA that has the methionine attached
• ribosome then reads the next 3 codons
• this calls for the tRNA that has glycine attached
• ribosome then links the methionine to glycine

Question 25

what happens when the ribosome links methionine to glycine?

Answer 25

• ribosome moves down another 3 nucleotides
• first tRNA is removed
• second tRNA with now 2 amino acids remain
• 3 tRNA moves in which carries a serine
• methionine linked to glycine is then attached to serine
• amino acid chain continues to grow until the ribosome reaches a stop codon

Question 26

what can happen if there is a DNA mutation

Answer 26

hemoglobin example:
- sickle-cell anemia is caused by a single nucleotide mutation in the hemoglobin gene and it changes an amino acid
- then changes the hemoglobin protein causing abnormal RBC