DNA- the triplet code Flashcards
what is a gene?
sections of DNA that contain the coded info for making polypeptides
what does the sequence of the DNA base determine?
the sequence of amino acids
why must there be a minimum of three bases that code for each amino acid?
- 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
how many possible different DNA codes are there?
64
why is the code known as a ‘degenerate code’?
most amino acids have more than one triplet code
what are triplet codes that don’t code for any amino acids called?
‘stop codes’
what are two other features of the code?
non overlapping, universal
what are the DNA molecules in prokaryotic cells like?
smaller, form a circle, aren’t associated with protein molecules so don’t have chromosomes
what are the DNA molecules in eukaryotic cells like?
larger, form a line (linear), occur in association with proteins to form chromosomes
when is the only time chromosomes are visible?
when they are dividing
how is DNA in chromosomes held in position?
by proteins
what is the thread of the chromosome called?
chromatid
what connects the chromatids together?
centromere
how many chromosomes do humans have?
46
why do humans have an even number of chromosomes?
they occur in homologous pairs
how many molecules of DNA does a chromosome hold?
1 molecule, contains many genes
what is a homologous pair?
two chromosomes that determine the same genetic characteristics but are not identical
what is the total number of chromosomes know as?
the diploid number
what are haploid cells?
a cell which only contains one chromosome from each pair. only contain 23 chromosomes
what is an allele?
section of DNA on a chromosome coding for one or more polypeptide
who found that DNA is the genetic material in the cell?
Hershey and Chase
what did Hershey and Chase do?
- 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
what was the conclusion of Hershey and Chase?
evidence DNA genetic material- showed how DNA can be passed from one bacterium to another.
