1.5 Nucleic Acids And Their Functions Flashcards
What is the definition of translation
Changing the words of one language into the words in another language that have the same meaning
What is the two stages of protein synthesis
Transcription and translation
What is translation
The process that changes the coded information of mRNA into the correct sequence of amino acids, forming a polypeptide
What’s the function of tRNA
To carry amino acids to the ribosomes
What is amino acid activation
The attachment of an amino acid to its transfer RNA (tRNA)
The tRNA attaches to a specific amino acid in the presence of an enzyme and ATP (requires energy)
3 functions of tRNA
- tRNA’s carry specific proteins
- The tRNA cannot pick up an amino acid unless the amino acid is activated
- The amino acid attachment site of a tRNA will bind to a specific amino acid, if energy is supplied
What is translation step one (name and what is it )
Step one is initiation
The mRNA molecule with the START CODON AUG attaches itself to the ribosome. Most polypeptide chains start with AUG which codes for the amino acid methionine
What is translation step two
The tRNA, with and anticodon complementary to the first codon on the mRNA, attaches itself to the ribosome
Hydrogen bonds bind to the three bases of the codon on the mRNA to the complementary bases of the anticodon in the tRNA
Translation step three
A second tRNA molecule attaches to the ribosome. It has an anticodon complementary to the second codon on the mRNA
Translation step four
Elongation
The amino acids attached to the two tRNA molecules are close enough for a peptide bond to form between them. A ribosomal enzyme catalyses the formation of this bond.
The first tRNA leaves the ribosome leaving its attachment site empty.
Translation step 5
The ribosome moves one codon along the mRNA strand
The second tRNA molecule now occupies the first attachment site. Leaving the second site free
A third comes to fill this site and a peptide bond forms between the second and third amino acid
Translation step six
The ribosome moves along the mRNA stand reading off the message a codon at a time.
As it moves, more tRNA’s attach to the ribosome bringing their animo acids.
The polypeptide chain grows
Translation step seven
Termination
This continues until a stop codon occurs in the mRNA. These donor code for amino acids
The mRNA separates from the ribosome and the completed polypeptide chain is released to the cytoplasm
One gene one polypeptide hypothesis
1940s radiation damage to DNA prevented a single enzyme from being made. This led to one gene one enzyme hypothesis
Enzymes are proteins so became one gene one protein hypothesis
Some proteins like haemoglobin consist of more then one polypeptide so it let to one gene one polypeptide hypothesis
Define a gene
A gene is a sequence of DNA bases that codes for a polypeptide
What is post translation modification
Polypeptides that made on ribosomes carry through the cytoplasm to Golgi body. In the Golgi the polypeptide is folded into secondary, tertiary or quaternary structures
What is a haemoglobin / how is it made
Folded tertiary structure
Combines with non protein groups
Four polypeptides are combined (quaternary = 4)
Alpha helix regions (secondary structure)
Definition of transcription
An exact written copy of something
What carries the information to build a protein from amino acids
Dna carries the information to build the amino acids
DNA doesn’t leave the nucleus
What is immense involved in carrying
The genetic code from DNA in nucleus to the ribosomes in the cytoplasm where protein is made
Function of ribosomes
Site of protein synthesis
What 3 parts make up each nucleotide
A phosphate group
A Penrose sugar
A base which contains nitrogen
What is a cistron
The cistron is a length of DNA that forms a mRNA molecule. A cistron is often equivalent to a gene and codes for a specific polypeptide
Step one of transcription
DNA unwinds as the hydrogen bonds between the base pairs ar broken by the enzyme DNA helicase
Step two of transcription
One of the two DNA strands acts as a template against which a matching RNA strand is formed. RNA nucleotides are attracted to complementary bases on the DNA strand.
Step 3 of transcription
The enzyme RNA polymerase binds to the template strand of DNA at the beginning of the sequence to he copied. The enzyme moves along the DNA forming bonds that add nucleotides one at a time to the RNA strand
Step 3 of transcription
The enzyme RNA polymerase binds to the template strand of DNA at the beginning of the sequence to he copied. The enzyme moves along the DNA forming bonds that add nucleotides one at a time to the RNA strand
Step 4 of transcription
RNA polymerase separates from the DNA strand when it reaches a ‘stop’ signal. The transcript is complete and the newly formed RNA detaches from the DNA
What are extrons
Parts of dna that do code for proteins
What are introns
Non coding regions of a gene - these sequences don’t actually code for a protein