DNA, Genes And Protein Synthesis Flashcards
What are 4 features of the genetic code?
Degenerate
Non-overlapping
Universal
Read in triplets (codons)
What is meant by the term degenerate?
More than one triplet codes for the same amino acid
What is meant by non-overlapping?
Each base is read once (as part of a triplet)
What is meant by universal?
The same triplet always codes for the same amino acid in living organisms
Describe the structure of DNA?
Made of DNA nucleotides containing deoxyribose, phosphate and nitrogenous base (A,C,T,G)
It is double stranded and hydrogen bonds between complementary base pairs form a helix shape
How is DNA in eukaryotic cells different to prokaryotic cells?
DNA in eukaryotes is long and linear, associated with histone proteins to form chromosomes
DNA in prokaryotes is shorter, circular and not associated with histone proteins
What is the genetic code?
The order of bases on DNA, consists of codons (triplets of bases that code for a particular amino acid
Define the term gene?
A sequence of bases on a DNA molecule that codes for a specific sequence of amino acids (polypeptide)
Define the term genome?
The complete set of genes in each cell of an organism
Define the term proteome?
The full range of proteins produced by the genome in that organism
What is a locus?
The fixed position on a chromosome occupied by a gene
What is an allele?
Different versions of the same gene, found at the same locus on a chromosome
What are exons and introns?
Exons = regions of DNA that code for amino acid sequences
Introns = non-coding regions of DNA
Where are introns located?
Introns are only present in eukaryotes not prokaryotes
They are found between exons in genes
What are the two different types of mutation?
Gene mutations
Chromosomes mutation
What are the two types of gene mutation?
Point mutation
Frame shift
What is a mutation?
A random change/alteration to the DNA base sequence which occurs randomly during DNA replication
What is a point mutation and give an example?
The mutation just effects one nucleotide/base
A base substitution ( a nucleotide in the DNA is replaced by another)
What are the three different ways a point mutation can affect the genetic code?
A new triplet codes for a different amino acid due to the change in its tertiary structure
Triplet codes for same amino acid due to degenerate code
Triplet codes for a stop codon
Why might a mutation not lead to a change in the amino acid sequence?
Genetic code is degenerate so mutation may end up coding for the same amino acid as the original triplet
Mutation occurs in an intron
What is a frame shift and give an example?
All the subsequent amino acids changed as bases shift
(Base deletion/insertion)
What is a mutagenic agent and give an example of this?
Factors that increase the rate of gene mutation
- Ionising radiation eg.UV or X-Ray, Gamma ray
- Asbestos
- Carcinogenic chemicals eg.tobaco
What is a chromosome mutation?
Change in the number or structure of a chromosome
What is a polyploid chromosome mutation?
When an individual has 3 or more sets of chromosomes rather than 2
What is a chromosome non-disjunction ?
When chromosomes fail to separate correctly in meiosis so individuals (gametes) have one extra or one few chromosome
When does chromosome non-disjunction occur?
During meiosis in anaphase as the sister chromatids don’t separate
Describe the structure of mRNA?
A long, single strand, ribose sugars and AUCG bases
It’s base sequence is complementary to the DNA it was transcribed from
What are the advantages of using mRNA instead of DNA for translation?
- mRNA is shorter and contains uracil = it breaks down quickly so no excess polypeptides are formed
- mRNA is singe stranded and linear so ribosomes move along strand and tRNA binds to exposed bases
- mRNA contains no introns
Describe the structure of tRNA
Single strand of nucleotides that are folded into a clover leaf shape due to hydrogen bonds
One end is an anticodon and the other end is an amino acid binding site
What is produced by transcription?
mRNA
What are the two stages of protein synthesis?
- Transcription
- Translation
Where does transcription take place?
In the nucleus
Describe the process of transcription?
DNA helicase unwinds and separates the double helix by breaking hydrogen bonds between complementary base pairs
It exposes bases on template strand, only one DNA strand acts as a template
Free rRNA nucleotides align to complementary base pair on template
In RNA uracil with pair with adenine
RNA polymerase binds to template strand at the start triplet joining adjacent RNA nucleotides by phosphodiester bonds until it reaches the stop triplet
Pre-mRNA is spliced removing introns to form RNA
What is produced by translation?
Polypeptides
Where does translation take place.
In the cytoplasm on ribosomes
Describe the process of translation?
mRNA associates with a ribosomes which binds to the start codon
A specific tRNA molecule which has a complementary anticodon hydrogen bonds which o the start code bringing a specific amino acid
As the ribosome moves along to the next codon another complementary specific tRNA anticodon binds until the stop codon
Two amino acids are joined by peptide bonds in a condensation reaction using ATP
What is meiosis?
A form of cell division that produces 4 genetically different haploid cells (gametes)
What is the purpose of meiosis?
Meiosis ensures that when the gametes fuse at fertilisation, the normal diploid number of chromosomes is restored.
Meiosisis also an important source of genetic variation
What is a diploid cell?
2n = there are pairs of each chromosome ( which are the same size and shape)
What s a haploid cell?
n = cells have a single copy of each chromosome
What is a homologous chromosome?
A pair of chromosomes (one maternal the other paternal) that have the same gene loci
What happens during meiosis I ?
The homologous chromosome are separated
- Crossing over where homologous chromosome forms a bivalent before equivalent portions of genes(different alleles) are exchanges at the chiasmata
- Independent segregation as homologous pairs randomly line up along the equator during metaphase I
What happens during metaphase II?
The sister chromatids are separated
4 genetically different haploid cells produced
Describe the differences between meiosis and mitosis?
Mitosis = 1 division, diploid daughter cells, genetically identical, chromosomes dealt with independently, chromatids separated, growth and repair
Meiosis = 2 divisions, haploid daughter cells, division of homologous pair and sister chromatids, form gametes for sexual reproduction
DNA replication determines whether the chromosome has 1 or 2 chromatids
Haploid or Diploid is whether each chromosome has a matching pair in the nucleus or not
DNA replication determines whether the chromosome has 1 or 2 chromatids
Haploid or Diploid is whether each chromosome has a matching pair in the nucleus or not
How does meiosis cause genetic variation by producing new allele combinations?
Crossing over (prophase 1)
Independent segregation (metaphase 1)
Random fertilisation of gametes
Random mating of organisms
Mutations during DNA replication
