8: DNA, Genes And Protein Synthesis Flashcards
What is a gene?
A section of DNA that contains the coded information for making polypeptides.
What is the structure of a gene?
It’s in the form of a specific sequences of bases along the DNA molecule.
Where is it located on the DNA molecule?
It is located at the locus on the DNA molecule.
What does a gene code for?
1: the amino acid sequence of a polypeptide
2: functional RNA, including ribosomal RNA and transfer RNA (tRNA)
What are the 3 main features of the genetic code?
1: Degenerate code
2: Non-overlapping
3: Universal
What does degenerate mean?
Most amino acids are coded for by more than one triplet
What does non-overlapping mean?
Each base in the sequence is only read once
What does universal mean?
That, with a few minor exceptions, each triplet codes for the same amino acid is all organisms
-> indirect evidence for evolution
What are the coding and non-coding sequences in genes called?
Coding = Exons
Non-coding = Introns
What are the 2 differences between the DNA in prokaryotic can eukaryotic cells?
1: in prokaryotic cells DNA molecules are shorter, form a loop and are not associated with a protein (not membrane bound) therefore, do NOT have chromosomes.
2: in eukaryotic cells DNA molecules are longer, are linear and are associated with proteins (histones) therefore they form chromosomes.
When are chromosomes only visible?
When a cell is dividing
-> mitosis/meiosis
What homologous chromosomes?
Homologous pairs consist of one maternal and one paternal chromosome
What is an allele?
It is many alternate forms of a gene
How is coded information on the DNA transferred to the cytoplasm where it is translated into proteins?
Sections of DNA code are transcribed onto a single-stranded molecule called ribonucleic acid (RNA)
What is the structure of RNA?
Pentose sugar
Organic base (adenine, guanine, cytosine, uracil)
Phosphate group
What is a genome?
A complete set of genes in cell, including those in the mitochondria and chloroplasts
What is a proteome?
A full range of proteins produced by the genome
What are the 2 types of RNA that are important in protein synthesis?
1: mRNA
Messenger RNA
2: tRNA
Transfer RNA
Which type of RNA transfers the DNA code from the nucleus to the cytoplasm?
Messenger RNA (mRNA)
What is a feature of mRNA that allows it to leave the nucleus?
It is small so it can leave too nucleus through nuclear pores.
What is the structure of mRNA?
Consists of thousands of mono-nucleotides
Long strand
Single helix
What is the function of mRNA?
Leaves the nucleus via nuclear pores and enters the cytoplasm where it acts as a template for protein synthesis.
What is the structure of tRNA?
Relatively small molecule
Made up of around 80 nucleotides
Single stranded chain folded into a clover-leaf shape
What is the function of tRNA?
There are many types of tRNA, each of which binds to a specific amino acid. At the other end of the tRNA molecule there is an anticodon which binds to specific codons during translation when complementary bases pair up.
Simply define transcription:
A complementary section of part of the DNA sequence is made in the form of pre-mRNA
What is the enzyme that causes the two DNA strands to separate in transcription?
DNA helicase
Which enzyme moves along the strand and joins nucleotides together in transcription?
RNA polymerase
Approximately how many bases are exposed not he DNA at any one time during transcription?
Only around 12
Simply define translation:
The mRNA is used as a template to which complementary tRNA molecules attach and the amino acids they carry are linked together to form a polypeptide.
What is needed to form a peptide bond between two amino acids during translation?
Enzyme peptidyl transferase and ATP which is hydrolysed to provide the required energy
What is splicing and why is it necessary?
Turns pre-mRNA into mRNA.
The base sequences corresponding to the introns (non-coding) are removed and the functional exons are joined together.
It is needed to ensure the mRNA molecule can fit through the nuclear pores.
Most prokaryotic cells do not have introns, therefore splicing is unnecessary.
