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Gen bio. ch. 17- FROM GENE TO PROTEIN

Terms in this set (23)

Codon
mRNA base triplets
mRNA
An RNA molecule transcribed from the DNA of a gene, and from which a protein is translated by the action of ribosomes. The basic function of the nucleotide sequence of mRNA is to determine the amino acid sequence in proteins.
Promoter
These are the sequences where gene's start. This is where RNA polymerase binds to the DNA change to initiate transciption. It is the beginning of the transcription unit.

They have specific sequences.
Terminator
The sequence where gene's end on a transcription unit of DNA.
tRNA
an adaptor molecule composed of RNA, typically 76 to 90 nucleotides in length, that serves as the physical link between the mRNA and the amino acid sequence of proteins.

The function of tRNA is
to transfer amino acids from the cytoplasmic pool of amino acids to a growing polypeptide in a ribosome.
anticodon
the particular nucleotide triplet that base-pairs
to a specific mRNA codon.
rRNA
Ribosomal RNA is the RNA component of the ribosome, and is essential for protein synthesis in all living organisms. It constitutes the predominant material within the ribosome, which is approximately 60% rRNA and 40% protein by weight.
reading frame
Reading the symbols in the correct
groupings—that is, in the correct reading frame. mRNA nucleotides are read from left to right (5' - 3')
in groups of three.

-UGG UUU GGC UCA
Intron
The noncoding segments of nucleic acid that lie
between coding regions

short for 'intervening sequences'
Exon
these segments are eventually expressed, usually by being translated into amino
acid sequences.
5' CAP
a modified form of a guanine (G)
nucleotide added onto the 5' end after transcription of the
first 20-40 nucleotides.
Poly-A-tail
At the 3' end, an enzyme then adds 50-250 more adenine (A) nucleotides
Functions of cap and poly-A-tail
1. they seem to facilitate the export of the mature mRNA from the nucleus.

2. they help protect the mRNA from degradation by hydrolytic enzymes.

3. they help ribosomes attach to the 5' end
of the mRNA once the mRNA reaches the cytoplasm.
How does RNA differ from DNA?
RNA's sugar is ribose
DNA's sugar is deoxyribose
How is the genetic code universal?
The RNA codon CCG, for instance,
is translated as the amino acid proline in all organisms
whose genetic code has been examined. In laboratory experiments, genes can be transcribed and translated after being transplanted from one species to another
What is transcription?
synthesis of RNA under the direction of DNA
Describe the process of transcription
1. Initiation. After RNA polymerase binds to the promoter,
the DNA strands unwind, and the polymerase initiates RNA synthesis at the start point on the template strand.

2. Elongation. The polymerase moves downstream, unwinding the DNA and elongating the RNA transcript 5 3. In the wake of transcription, the DNA strands re-form a double helix.

3. Termination. Eventually, the RNA transcript is released, and the polymerase detaches from the DNA.
Translation Initiation
1. initiation brings together mRNA, a
tRNA bearing the first amino acid of the polypeptide, and
the two subunits of a ribosome. This is followed by the attachment of a large ribosomal subunit, completing the translation initiation complex.
Translation elongation
amino acids are added one by one to the previous amino acid at the C-terminus of the growing chain.
Translation termination
Elongation continues until a stop codon in the mRNA
reaches the A site of the ribosome.

A release factor, a protein shaped like an aminoacyl tRNA, binds directly to the stop codon in the A site. The release factor causes the addition of a water molecule instead of an amino acid to the polypeptide chain. This hydrolyzes the
the bond between the completed polypeptide
and the tRNA in the P site, releasing the polypeptide
through the exit tunnel of the ribosome's large subunit.
RNA processing
1. Alteration of mRNA ends. 5' end receives 5' cap and 3' end receives poly-A-tail

2. RNA splicing there is the removal of introns and the splicing together of exons (forming a continuous coding sequence) The removal of introns is accomplished by a large complex made of proteins and small RNAs called a spliceosome.
Why do base-pair insertions have a greater affect than substitutions?
Insertion or deletion of nucleotides may alter the reading frame of the genetic message, the triplet
grouping of nucleotides on the mRNA that is read during
translation. Doesn't happen with substitutions
Mutagenesis
(1) single nucleotide-pair substitutions
and (2) nucleotide-pair insertions or deletions. Insertions
and deletions can involve one or more nucleotide pairs.

Can be inherited. Also from radiation exposure
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