Chapter 8 - DNA, genes and protein synthesis Flashcards
What is a gene?
A gene is a sequence of DNA bases that code for either a polypeptide or RNA
How are genes involved in making proteins?
The order of DNA bases on a gene determines the order of amino acids in a particular polypeptide. This polypeptide then determines the primary structure of a protein
How many bases code for one amino acid?
Three
What is functional RNA?
RNA molecules, other than mRNA that perform special tasks during protein synthesis
*What is a cell’s genome?
The complete set of genes in a cell
*What is a cell’s proteome?
The full range of proteins a cell is able to produce
What are most amino acids coded by?
Between two and six triplets
What will all chains of amino acids start with?
Methionine - the start codon
What will all chains of amino acids include?
A stop codon
What does the term ‘non-overlapping’ mean?
Each base is read only once
What are introns?
Non-coding parts of DNA
What is a DNA molecule in a prokaryotic cell like?
The DNA molecules are carried as chromosomes, but are shorter and circular. The DNA supercoils to fit in the cell
What is eukaryotic DNA like?
It is a linear molecule that exists as chromosomes. The DNA molecule is so long that it must be would around proteins, called histones, to fit in the nucleus. This creates compact chromosomes
Which organelles in eukaryotic cells also have their own DNA?
Mitochondria and chloroplasts, but it is circular and shorter than other DNA in the nucleus
What are homologous pairs?
Pairs of matching chromosomes, which are the same size and have the same genes
*What are alleles?
Different forms of genes
What is the diploid number?
The total number of chromosomes in an organism
How do alleles differ?
They contain different base sequences so code for different proteins, which create different versions of the same polypeptide.
What are exons?
Sections of genes that code for amino acids
What are non-coding repeats?
Sections of DNA that are repeating (e.g. CTTCTTCTT) but don’t code for amino acids
How many different amino acids are there?
20
Why is DNA degenerate?
Most amino acids are coded for by more than one triplet
Why is the genetic code described as universal?
The same triplet codes for the same amino acid in all living organisms
How do you get the mRNA sequence from a DNA sequence?
You use the complimentary base pairs, but always switch T for U
What does T stand for?
Thymine
What does A stand for?
Adenine
What does G stand for?
Guanine
What does U stand for?
Uracil
What does C stand for?
Cytosine
What is a codon?
A triplet of bases that code for one amino acid
How do you work out tRNA from mRNA?
The complementary pairs (tRNA contains uracil, not thymine)
How do you work out the sequence of amino acids from a section of mRNA?
Break it down into codons and use information in the table provided
How are di-nucleotides formed?
Two nucleotides join together in a condensation reaction between the sugar on one nucleotide and the phosphate on another
What bond is formed in polynucleotides?
Phosphodiester
What are the purine bases?
Guanine and adenine
What are the pyrimidine bases?
Thymine, uracil and cytosine
What is RNA made from?
A single polynucleotide strand in which each nucleotide is made from a ribose sugar, a base (A, C, G, U) and a phosphate group
Function of mRNA
After it is formed through transcription, it exits the nucleus through nuclear pores, where it travels to the ribosome. It acts as a template for protein synthesis
Structure of tRNA
A single-stranded molecule which is folded into a clover leaf shape, held in place by strong hydrogen bonds between complementary bases. At one end, there is an anticodon, which is complementary to the triplet on the mRNA, and at the other there is an amino acid bonding site
Function of tRNA
It carries amino acids used to make proteins to the ribosome
What is transcription?
The formation of pre-mRNA from DNA through complementary base pairing
What is translation?
mRNA and tRNA are used to convert the genetic code into the polypeptide chains needed to form proteins
Process of transcription
DNA helicase breaks the hydrogen bonds between nucleotides
This causes the double helix to unravel
One of the strands acts as a template strand. Using this, RNA polymerase attaches complementary nucleotides from the cytoplasm to the exposed strand
As the polymerase moves through the molecule and assembles the pre-mRNA, the double helix rejoins behind it and hydrogen bonds reform
When the polymerase reaches a stop codon, it stops and detaches
Why doesn’t pre-mRNA need to be spliced in prokaryotes?
There are no introns in prokaryotes’ DNA
How are introns removed from eukaryotic DNA?
Splicing
What happens to pre-mRNA to make mRNA?
It is spliced - introns are removed and exons are joined together
What happens to a polypeptide chain after it has been made?
It is coiled to form the secondary structure
The secondary structure is coiled to form the tertiary structure
Different polypeptide chains are linked to form the quaternary structure
Process of translation
A ribosome becomes attached to the mRNA
A tRNA molecule, carrying an amino acid, with a complementary anticodon to the codon on the mRNA sequence attaches itself to the mRNA by complementary base pairing
A second tRNA molecule attaches to the mRNA in the same way
The two amino acids attached to the tRNA molecules join together with a peptide bond
The first tRNA molecule moves away, leaving the amino acid behind
A third tRNA molecule attaches to the mRNA
By the same process, its amino acid joins to the two amino acids already there
The second tRNA molecule moves away
This continues until the stop codon is reached. The polypeptide chain moves away from the ribosome; translation is complete
What differs between amino acids?
The ‘R’ group
Do tRNA molecules have hydrogen bonds?
Yes
Which molecules are made from a single polypeptide strand?
mRNA and tRNA
