DNA- the triplet code

Question 1

what is a gene?

Answer 1

sections of DNA that contain the coded info for making polypeptides

Question 2

what does the sequence of the DNA base determine?

Answer 2

the sequence of amino acids

Question 3

why must there be a minimum of three bases that code for each amino acid?

Answer 3

• Only 20 amino acids regularly occur in proteins
• Each amino acid has its own code of bases on the DNA
• Only 4 different bases are present in DNA
• Using pair of bases- only 16 different codes possible

Question 4

how many possible different DNA codes are there?

Answer 4

64

Question 5

why is the code known as a ‘degenerate code’?

Answer 5

most amino acids have more than one triplet code

Question 6

what are triplet codes that don’t code for any amino acids called?

Answer 6

‘stop codes’

Question 7

what are two other features of the code?

Answer 7

non overlapping, universal

Question 8

what are the DNA molecules in prokaryotic cells like?

Answer 8

smaller, form a circle, aren’t associated with protein molecules so don’t have chromosomes

Question 9

what are the DNA molecules in eukaryotic cells like?

Answer 9

larger, form a line (linear), occur in association with proteins to form chromosomes

Question 10

when is the only time chromosomes are visible?

Answer 10

when they are dividing

Question 11

how is DNA in chromosomes held in position?

Answer 11

by proteins

Question 12

what is the thread of the chromosome called?

Answer 12

chromatid

Question 13

what connects the chromatids together?

Answer 13

centromere

Question 14

how many chromosomes do humans have?

Answer 14

46

Question 15

why do humans have an even number of chromosomes?

Answer 15

they occur in homologous pairs

Question 16

how many molecules of DNA does a chromosome hold?

Answer 16

1 molecule, contains many genes

Question 17

what is a homologous pair?

Answer 17

two chromosomes that determine the same genetic characteristics but are not identical

Question 18

what is the total number of chromosomes know as?

Answer 18

the diploid number

Question 19

what are haploid cells?

Answer 19

a cell which only contains one chromosome from each pair. only contain 23 chromosomes

Question 20

what is an allele?

Answer 20

section of DNA on a chromosome coding for one or more polypeptide

Question 21

who found that DNA is the genetic material in the cell?

Answer 21

Hershey and Chase

Question 22

what did Hershey and Chase do?

Answer 22

• been observed viruses infect bacteria, causing bacteria to make more viruses
• protein and DNA in viruses were labelled with different radioactive elements
• one sample bacteria (e coli) infected viruses with radioactive protein, other infected bacteria with radioactive DNA
• the virus and bacteria were separated from each other
• only sample with bacteria injected with virus with radioactive DNA showed any sign of radioactivity

Question 23

what was the conclusion of Hershey and Chase?

Answer 23

evidence DNA genetic material- showed how DNA can be passed from one bacterium to another.