Chapter 8 DNA, genes and protein synthesis Flashcards
what is the definition of a chromosome
A thread like structure that is made of protein and DNA used to pass hereditary information to the next generation
What is the definition of a centromere
a centromere joins two chromatids together and attaches to spindle fibres
what is the definition of a chromatid
One of the two strands of a chromosome that are joined by a centromere
what is the definition of a gene
a section of DNA that codes for a polypeptide or a function RNA
what is the definition of an allele
an alternative form of a gene
what is the definition of a locus
the position of a gene on a chromosome or a DNA molecule
what is the definition of homologous chromosomes
A pair of chromosomes, one maternal and on paternal, that have the same gene loci and determine the same features
what is the definition of the genome
The complete set of genes in a cell
what is the definition of the proteome
The full range of proteins that the cell can produce
What are the differences between DNA in eukaryotes and prokaryotes
What are the two types of RNA in proteins synthesis
mRNA (messenger RNA)
tRNA (transfer RNA)
What is the function of mRNA
and what is it’s structure
mRNA transfers genetic information from DNA in the nucleus to the ribosomes in the cytoplasm for protein synthesis
It has a single helix structure.
What is the function of tRNA and what is its structure
tRNA carries specific amino acids to the ribosomes for protein synthesis
It is a single strand folded into a clover leaf shape, held together by hydrogen bonds between complementary base pairing. it has a specific amino acid attachment site, and a base 3 anticodon
Compare DNA, mRNA and tRNA
How do you prove that each amino acid is coded for by 3 bases
There are 20 naturally occurring amino acids
There are 4 bases on DNA
1 base coding for 1 amino acid = (4) = 4 amino acids
2 bases coding for 1 amino acid = (44) = 16 possible combinations (not enough)
3 bases coding for 1 amino acid = (44*4) 64 possible combinations (enough)
Therefore, each amino acid is coded for by 3 bases
what are the three main features of the genetic code
the genetic code is: universal, non-overlapping and degenerate
what does genetic code being universal mean
Each triplet codes for the same amino acid in all species of organisms. This demonstrates evolution from a common ancestor
what does genetic code being non-overlapping mean
Each base in a triplet is only read once. Triplets are discrete
what does genetic code being degenerate mean
Most amino acids are coded for by more than one triplet.
what are introns and exons
Introns - non-coding sections of DNA
Exons - coding sections of DNA
What are the effects of a change in the base sequence of amino acids on a protein.
If there is a change in base sequence, this leads toa change in amino acid sequence / primary structure
This leads to a change in hydrogen,ionic, anddisulphide bonds
This alters the tertiary structure of the protein (If the protein is an enzyme, it leads to a change in the shape of the active site so enzyme-substrate complexes cannot form).
What are the main features of transcription
- Occurs in the nucleus
- In eukaryotes, pre-mRNA is produced from DNA. This is then spliced to form mRNA
- In prokaryotes, mRNA is produced from DNA
What are the stages of trascription
DNA unwinds and DNA helicase breaks H bonds between complementary DNA bases, separating DNA strands and exposing DNA bases
One DNA strand acts as the template strand
Free RNA nucleotides align with the template strand DNA bases by complementary base pairing. A – U, T – A, C – G, G – C
Adjacent RNA nucleotides joined by RNA polymerase (condensation reaction) moving from 5’ to 3’ end
In eukaryotes pre-mRNA is formed. In prokaryotes, mRNA is formed
Picture of transcription
What is splicing
Transcription forms pre-mRNA from DNA
DNA includes introns and exons
Pre-mRNA therefore contains non-coding introns
Splicing is the removal of introns from pre-mRNA to form mRNA
mRNA now leaves the nucleus through the nuclear pores and attaches to a ribosome in the nucleus
diagram for the steps in splicing
What are the main features of translation and what is translation
translation is the production of polypeptides from codons on mRNA
Occurs on ribosomes
Involves ribosomes, tRNA, amino acids and ATP
what are the stages in translation
1.mRNA attaches to a ribosome
2.Ribosome moves to the start codon (AUG) on the mRNA
3.tRNA brings specific amino acid to the ribosome
4.Anticodon on tRNA binds to thecomplementary codon on mRNA by complementary base pairing
5.Ribosome moves along to next codon. Ribosome can fit two tRNAs on it at a time
6.Process repeated, and amino acids join by condensation reaction with peptide bonds to form polypeptide, using energy from ATP
7. mRNA detaches from the ribosome at the stop codon
image for translation
