Topic 6: Nucleic Acids and Protein Synthesis Flashcards
Allele
Alternative forms of a gene. For example, there are three different alleles or forms of the gene which codes for the antigen on the red blood cells which determines blood group types. These alleles are IA, IB, IO. It is important to note that a gene controls the production of a protein for a given characteristic but that alleles control different forms of this protein for the given characteristic.
Anticodon
A sequence of three unpaired bases on a tRNA molecule that binds with a codon on mRNA on the ribosome during protein synthesis.
Codon
A sequence of three bases on the mRNA molecule that codes for a specific amino acid or for a start or stop signal during protein synthesis.
Complementary Bases
DNA consists of two polypeptide chains or strands which are liked by hydrogen bonds between the bases. The base Adenine (A) can only pair with Thymine (T) as they both form two hydrogen bonds. The base Cytosine can only pair with Guanine (G) as they form three hydrogen bonds. Complementary base pairing is essential to the understanding of DNA replication and protein synthesis.
DNA
DNA is deoxyribonucleic acid. It is a nucleic acid made up of nucleotides which contain the sugar deoxyribose, a phosphate, and one of the bases Adenine, Guanine, Cytosine or Thymine. DNA consists of two polynucleotide strands that run antiparallel (in opposite directions) to each other and they are linked by hydrogen bonds between their complementary base pairs. The two DNA strands are twisted to form a double helix. the helical arrangement and the hydrogen bonds between bases help to make the DNA molecule very stable.
DNA Helicase
An enzyme that separates the two stands of DNA by breaking the hydrogen bonds between the bases during DNA replication.
DNA Ligase
An enzyme that catalyse the joining of segments of the nucleotides on the lagging strands of DNA during DNA replication.
DNA Polymerase
An enzyme that catalyses the joining of free nucleotides in the nucleus to the exposed bases on the DNA strands by complementary base pairing during DNA replication.
DNA Replication
DNA replication is the process by which the DNA molecule can produce an exact copy of itself. DNA replication is described as being semi-conservative as each new DNA molecule contains one old and one new strand.
Gene
A section of DNA on a chromosome that codes for a protein according to the instructions of its nucleotide base sequence. Gene determine the activities of cells and the feature of organism.
Locus
The position of a gene on a chromosome.
Mutation
An unpredictable chance in the structure of DNA, or in the structure and number of chromosomes. All genes were originally produced as gene mutation.
Nucleic Acid
Nucleic acids, which include DNA (deoxyribonucleic acid) and RNA (ribonucleic acid), are made from monomers known as nucleotides. The term polynucleotide has the same meaning as nucleic acid. The term nucleic acid is used because this category of molecule was first located in the nucleus and is acidic in nature. Each nucleotide has three components: a 5-carbon sugar, a phosphate group, and a nitrogenous base. If the sugar is deoxyribose, the polymer is DNA. If the sugar is ribose, the polymer is RNA. Nucleotides are joined together through a phosphodiester bond between the pentose sugar of one nucleotide and the phosphate group of another nucleotide through a condensation reaction.
Nucleotide
A nucleotide is thee building block of nucleic acids. Each nucleotide has three component: a pentose sugar, a phosphate and an organic nitrogenous base.
Peptidyl Transferase
This enzyme is found in the small subunit of a ribosome. It catalyzes the reaction that forms peptide bonds between two amino acid during translation.
Protein Synthesis
Protein synthesis occurs in all cells at the ribosomes and involves the assembly of amino acids in the correct order into polypeptide chains as directed by the genetic code on the DNA. Polypeptides are later modified into protein.
Purine
Purine are nitrrogenous bases which are larger than pyrimidines and have a double ring structure. Adenine and Guanine are purine molecules.
Pyrimidine
Pyrimidines are nitrogenous bases which are smaller than purines and have a single ring structure. Thymine, Cytosine and Uracil are pyrimidine molecules.
Ribosome
Ribosomes are tiny organelles found in large numbers in both prokaryotic and eukaryotic cells. They are made from protein and ribosomal RNA (rRNA). They consist of two subunits. They are the site of protein synthesis in cells.
RNA
RNA is ribonucleic acid. It is a nucleic acid made up of nucleotides which contain the sugar ribose, a phosphate, and one of the bases adenine, guanine, cytosine or uracil. RNA nucleotides are polymerized to produce a single polynucleotide chain. There are three types of RNA: messenger RNA (mRNA), transfer RNA (tRNA) and ribosomal RNA (rRNA).
Messenger RNA, mRNA
This is formed in the nucleus in a process called transcription. It has a single helix twisted into a helix whose length and base sequence vary. It has a short life and it is involved in protein synthesis.
Ribosomal RNA, rRNA
This is formed in the nucleus and it forms over half the mass of a ribosome.
Transfer RNA, tRNA
This has a single chain folded into a clover leaf shape. There are at least 20 types of tRNA. The structure is always similar except for the three bases of the anticodon which determines which amino acids attaches. tRNA is involved in protein synthesis.
Substitution Mutation
A mutation is a change in DNA which can cause a change to the protein synthesized. A substitution mutation is where one or more bases on the DNA are replaced by a different base. This may cause one amino acid to be changed. As a result the protein coded for by the gene on the DNA where the substitution mutation occurred may not function and so harm the organism.
Transcription
This is the process that occurs in the nucleus when a molecule of mRNA is produced from one strand of a DNA molecule which acts as a template.
Translation
The production of a polypeptide on a ribosome from the codons on the mRNA using tRNA molecules to transfer the amino acids to the mRNA on the ribosome.
Triplet Code
The sequence of nucleotide bases in a DNA molecule is a code for the sequence of amino acids in a polypeptide. This code is called a trplet code as it is a triplet or a three letter code. Each sequence of three bases on three consecutive nucleotides codes for one amino acid. There are 64 different triplets of DNA bases which code for the 20 different amino acids. The genetic code is described as being a degenerate code because some amino acids are coded for by more than one triplet of DNA bases.
Universal Code
The DNA base triplets code for the same amino acids in all organisms whether bacteria or grass or human and the genetic code is therefore described as a Universal Code. This has made the development of gene technology possible as it means that genes from one organism can be inserted into a different organism where the gene can still fuction to produce the same protein in the new organism.
