Chapter 8 Flashcards
(40 cards)
What is the definition of a gene?
Is a section of DNA that contains the coded info for making polypeptides + functional RNA
What form is coded information in?
In the form of a specific sequence of bases along the DNA molecule
What do genes determine?
Determine proteins of an organism
+
Nature and development of all organisms
Where is the gene located?
Located at a particular position called locus
The gene is a base sequence that codes for……
Amino acid sequence of a polypeptide
or functional RNA (ribosomal RNA + tRNA)
Why must there be a minimum of 3 bases that code for each amino acid?
- Only 20 different AA regularly occur in proteins
- Each AA must have its own code of bases on DNA
- Only 4 bases(A,T,G,C)
- 3 bases produce 64 (4^3) different codes, more than enough to satisfy requirements of 20 amino acids
What is a code that has 3 bases for each AA called?
A TRIPLET
What are some feautures of a genetic code
- Few AA coded by only a single triplet (remaining coded between 2+6 triplets)
- Triplets always read in 1 particular direction along DNA strand
- Start of DNA sequence codes for a polypeptide always same triplet
- Code is universal
Why is the genetic code also known as the ‘degenerate code’
Because most amino acids are coded for more than 1 triplet
What does it mean if the code is non-overlapping?
Each base in sequence is read-only once (e.g 123456 would be read as 123 , 456)
What are introns?
…
What are extrons?
…
Why is much of DNA in eukaryotes does not code for polypeptides?
between genes, there are non-coding sequences made up of multiple repeats of base sequences
Describe the RNA structure?
- Pentose sugar
- Organic bases (A,T,G,U)
- Phosphate group
What two types of RNA are important for protein synthesis?
mRNA
tRNA
What is the structure of the mRNA?
-Long strand arranged in a single helix (Consisting of thousand of mononucleotides)
How is the structure of mRNA suited to its function?
it possesses info in form of codons
-The sequence of codons will determine AA sequence of a specific polypeptide that will be made
What are codons?
A sequence of 3 adjacent (bases) adjacent nucleotides in mRNA that codes for one amino acid.
What happens to mRNA when its formed in the nucleus?
mRNA leaves the nucleus via pores in nuclear pores + enters the cytoplasm
- Associates with ribosomes + acts as a template for protein synthesis
What is the structure of tRNA?
Relatively small molecules (made of 80 nucleotides)
- Single-stranded folded into a clover shape
- Part of mRNA which amino acid can attach easily
What is in the opposite end of tRNA?
Anticodons (sequence of 3 other organic bases)
Because the genetic code is degenerate there must be…
as many tRNA as there are coding triplets
however
each tRNA is specific to each AA + each AA is specific to the anticodon
What is an anticodon?
A sequence of 3 adjacent molecules on a molecule of tRNA that is complementary to a particular codon on a mRNA
What is an Allele?
One of a number of alternative forms of a gene
