Protein Synthesis Flashcards
What are the two types of nucleic acid?
DNA and RNA
What are nucleic acids made up of?
Nucleotides
What is a nucleotide?
The monomer from which nucleic acids are formed
What is a nucleotide made up of?
Pentose sugar, nitrogenous base and a phosphoric acid
Are purines double or single ring bases?
Double
What bases are purines?
Adenine and guanine
Are pyrimidines double or single ring bases?
Single
What bases are pyrimidines?
Cytosine, thymine and uracil
What reaction makes up a nucleotide?
Condensation
What reaction joins nucleotides together?
Condensation reactions
What bonds hold nucleotides together?
Phosphodiester bonds
What does DNA polymerase do?
Catalyses the formation of a phosphodiester bond between two nucleotides
What is a phosphodiester bond?
Covalent bond between two nucleotides
What is a nucleic acid?
A very long thread-like macromolecule
How long are RNA molecules?
Relatively short - between 100 and thousands of nucleotides
What pentose is in RNA?
Ribose
What bases are in RNA?
Adenine, cytosine, guanine and uracil
What are the three functional types of RNA?
messenger RNA, transfer RNA and ribosomal RNA
What does mRNA do?
Carries a copy of a single gene to a cell’s ribosome
What does tRNA do?
Carries individual amino acids to the ribosomes during protein synthesis
What does rRNA do?
Forms the subunits of the ribosomes
How long are DNA molecules?
Very long, several million nucleotides
What is the pentose in DNA?
Deoxyribose
What are the bases in DNA?
Adenine, cytosine, guanine and thymine
How many polynucleotide strands in a DNA molecule?
Two
How many polynucleotide strands in a RNA molecule?
One
What bonds hold the polynucleotide chains together in DNA?
Hydrogen
Where are H bonds found in DNA?
Between complementary base pairings between strands
What are the complementary base pairings in DNA?
Adenine and thymine, cytosine and guanine
Why are DNA strands antiparallel?
So that the two strands fit together
Explain DNA replication
DNA helicase breaks H bonds between comp. base pairings and unwinds helix
Separated strands act as a template w exposed bases
Free nucleotides are attracted to complementary bases on strand and H bonds form
DNA polymerase reforms phosphodiester bonds and proof reads DNA
DNA ligase joins segments of DNA together
Why is it called semi conservative replication?
Because in the newly formed DNA molecule there is one parent strand from the original DNA molecule
What is the major role of DNA?
To make specific proteins
What is a gene?
A sequence of DNA nucleotide bases that encodes for the sequence of amino acids to form a single polypeptide chain
What is meant by the genetic code being universal?
The same triplets code for the same amino acids in all organisms
How many possible triplet combinations are possible with 4 bases?
64
What does degenerate mean?
Some amino acids are coded for by more than one base triplet
What is a codon?
Nucleotide base triplet on mRNA that encodes for a single amino acid
What is the antisense strand?
The polynucleotide strand in a DNA molecule that is always used in protein synthesis to determine the order of amino acids in a polypeptide
What is meant by non-overlapping?
Each base pairing is only used in one triplet
What does transcription do?
Forms a molecule of mRNA
Explain the process of transcription
DNA helicase unwinds helix and breaks H bonds
Separated into sense and antisense strand
Antisense strand used as template with exposed bases
Complementary RNA nucleotides attracted to exposed bases and H bonds form
RNA polymerase reforms phosphodiester bonds between RNA nucleotides and mRNA is formed
Leaves nucleus via nuclear pores to fo to ribosomes
How many amino acids involved in protein synthesis?
20
Describe the structure of the tRNA molecule
One end has a site for the amino acid to join on to and the other end has anticodon specific to an amino acid
How are amino acids activated?
Specific enzymes join specific amino acids to their specific tRNA molecules
Explain translation
Ribosomes attach to the mRNA molecule and read the codons
Complementary anticodons on the tRNA molecules slot into place in the ribosome and held in place by temporary H bonds
Amino acids on the tRNA join together in condensation reactions to form peptide bonds
tRNA molecules are then free to go back to the cytoplasm and be reused
Process stops at stop codons
What are introns?
Non coding sections of DNA
What are extrons?
Coding sections of DNA
What is splicing?
When introns are cut out of the pre mRNA before it leaves the nucleus
What is a gene mutation?
A random and unpredictable change in the number or sequence of bases in a single gene
What are mutagens?
Factors that increase the chance of a mutation
What are some examples of mutagens?
Radiation like x rays and chemicals
What is a base deletion?
When one or more bases are lost from the sequence
What is a base insertion?
When one or more bases are inserted into the sequence
What is a base substitution?
When one or more bases are changed for a different base
What is a point mutation?
When a gene mutation only involves one base
What is sickle cell anaemia and how does it arise?
When oxygen cannot be transported efficiently because of a point mutation (base substitution) in the gene that codes for haemoglobin which causes the haemoglobin to clump togetherand form long fibres