Protein Synthesis Flashcards
What is a locus
A gene located in a particular position on dna
How many amino acids regularly occur in proteins
20
What does degenerate refer to
Most amino acids are coded for by more than 1 triplet
What does non overlapping mean
Each base is part of only one triplet
What does it mean when the genetic code is universal
Each triplet codes for the same amino acid in all organisms
What are exons
Base sequences coding for sequence of amino acids
What are introns
Non coding sequences
What is the difference between prokaryotic and eukaryotic DNA
In prokaryotic cells, there is no nucleis and the dna molecules are short, circular, contain plasmids and are not associated with proteins. In eukayotic cells there is a nucleus with nuclear envelope and the dna molecule is very long, linear, associated with histones (proteins) and contains no plasmids
How is a chromosome formed
Dna molecules, in association with histones, form chromosomes
What is significant about the mitchondria and chloroplasts of eukaryotic cells
Contain dna similar to prokaryotes: short, circular and not associated with proteins
What is a gene
A base sequence of dna that codes for the amino acid sequence of a polypeptide and functional RNA (including ribsomal rna and trna)
Where is a gene located
A gene occupies a fixed position called a locus on a particular dna molecule
What are 3 features of the genetic code
Universal, non overlapping and degenerate
Much of the nuclear dna in eukaryotes doesn’t what
Code for polypeptides
What is a homologuous pair
Two chromosomes that cary the same genes but not the same alleles of the genes
What is an allele
One of a number of alternate forms of a gene
What is the genome
The complete set of genes in a cell (including those in mitochondria and chloroplasts)
What is the proteome
The full range of proteins produced by a cell/ genome
What is rna
A single stranded polymer, made up of repeating mononucleotide subunits
Describe the structure of an rna nucleotide
Contains the pentose sugar RIBOSE, a phosphate group and one of the organic bases A,C,G or URACIL
Describe the structure of mrna
Long, single, linear strand with no hydrogen bonds. Its length and quantitity varies as its base sequence is determined by dna. It also has codons (3 bases complementrary to dna) amd its structure is less stable than trna and dna
Describe the structure of trna
Small, single strand folded into clover leaf shape. It contains hydrogen bonds and has an anticodon which is specific to one amino acid. Its length stays the same
Describe the process of transcription
- Dna helicase unwinds and unzips the dna molecule, breaking H bonds and exposing bases on a template strand 2. Free activated rna nucleotides pair with complementary bases 3. Rna polymerase joins nucleotides into strand until stop code is reached 4. Pre mrna detaches and is spliced into mrna by removing introns 5. Mrna leaves nucleus via pore into cytoplasm where it attaches to ribosome
What is the difference between prokaryotic and eukaryotic transcription
In prokaryotic cells, transcription directly results in the production of mrna from dna but in eukaryotic cells, transcription produces pre mrna which is spliced (removing introns) to form mrna
Describe the process of translation 1-3
- A ribosome attaches to the start codon on mrna 2. The trna molecule with the complementary anticodon sequence moves to ribosome and pairs with codon on mrna, the trna carries a specific AA 3. A trna molecule with complementary anticodon pairs with next codon on mrna, trna carries another AA
Describe the process of translation 4-7
- The ribosome moves along the mrna, brining together 2 trna molecules at a time 5. The 2 amino acids on trnas are joined by a peptide bond using an enzyme and energy from atp 6. Ribosome moves to 3rd codon, linking AAs on 2nd & 3rd trnas and the 1st is released & free to collect another AA = polypeptide is formed 7. Process continues until ribosome reaches stop code
What is a gene mutation
A change in the quantity or base sequnce of dna/ chromosomes
Gene mutations can arrise spontanously during dna replication, true or false?
True
What types of gene mutations are there
Base substitution and base deletion
What happens in substitution of bases
A nucleotide in a dna molecule is replaced with another nucleotide that has a different base
What can be the effects of a substitution of bases
The primary structure will differ so a different polypeptide may be produced, means bonds that form tertiary structure may change so the shape of active site may change so its no longer complementary to substrate to form ecs
Why do not all base substitutions have an effect
Not all cause a change in the sequence of AAs as the genetic code is degenerate (most AA coded for by more than one base triplet/codon)
What problem does base deletion cause
Sequences of dna are read in units of 3 so a deleted nucleotide cause all triplets to be read differently as each has been shifted to the left by one. This can create different polypeptides (won’t function correctly)
What is a chromosome mutation
Changes in the structure or number of whole chromosomes
What are the two forms of chromosome mutation
1.changes in whole sets of chromosomes, where organisms have 3 or more sets (polyploidy) 2.changes in number of chromosomes, where pairs fail to separate in meiosis (non disjunction) so gamete has 1 more/ less chromosome
What are mutagenic agents (give examples)
Exposure to mutagenic agents can increase the rate of mutations, examples are high energy ionising radiation (alpha, beta, gamma radiation) and chemicals like nitrogen dioxide or benzopyrene (in tabacco)
What is one advantage of showing the genetic code as base sequences on mRNA rather than dna
As ribosomes assemble polypeptides using the mRNA code. Dna has 2 strands, each with a different complementary base sequence
