B8 DNA, Genes, Protein Synthesis Flashcards
What are the characteristics of eukaryotic cells?
Very long
Linear
DNA associated with proteins called histones
80s Ribosome
What are the characteristics of prokaryotic cells?
Short
Circular
Not associated with proteins
70s Ribosomes
Why is the DNA Double helix wound around the histones?
So it takes up as a little space as possible so it can fit in the nucleus and the histones support the DNA
What do DNA and histones form when they are coiled up very tightly?
Chromosomes
What 2 organelles also contain their own DNA and what are their characteristics?
The mitochondria and chloroplasts contain DNA which is short, circular and not associated with proteins
What is a Gene?
A Gene is a base sequence of DNA that codes for either the amino acid sequence of a polypeptide or a functional RNA ( rRNA or tRNA)
Which position does a gene occupy?
A gene always occupies a fixed position locus on a particular DNA molecule
Definition of a Genome
The full set of genes in a cell
Definition of a proteome
The full range of proteins a cell is able to produce
What are the 3 main factors of genetic code?
Universal
Degenerate
Non overlapping
What does it mean by genetic code being universal?
Same code is used in all living organisms
What does it mean by genetic code being degenerate?
This means that more than one triplet codes for the same amino acid, reducing the number of mutations which are mistakes in the base.
What does it mean by genetic code being non overlapping?
This means that each triplet is only read once and triplets dont share any bases
What are the 2 areas of non-coding DNA?
Introns within genes
Non coding multiple repeats of bases sequences between genes
What are introns?
Section of genes that dont code for anything. Non coding sequences
Where do introns need to be removed?
Introns need to be removed before translation in gene splicing
What are non coding multiple repeats of base sequences?
They are just the same base sequence repeated many times
What are coding sequences called?
Exons
What do exons do?
They are coding regions and they are expressed in the phenotype to make proteins
What does mRNA stand for?
mRNA stands for messenger rna
What is the function of messenger RNA?
It transfers genetic information from DNA to ribosomes, where it acts as a template for protein synthesis
What does tRNA stand for?
tRNA stands for transfer rna
What is the function of Transfer RNA?
Transfers amino acids that are used to make proteins to ribosomes
Describe the structure of messenger RNA?
Very long single polynucleotide strand
Consists of polymer of RNA nucleotides
Possesses information in form of codons
What does the sequence of codon determine?
It determines the amino acid sequence of a specific polypeptide that will be made
Describe the structure of Transfer RNA?
Shorter single polynucleotide strand
H bonds between specific base pairs causes the trna molecule folds into a cloverleaf shape
At one end, a specific sequence of three bases = anticodon. At the other end is an amino acid binding site
What does ATP provide the amino acid and the TRNA molecule?
ATP provides the energy for the bond to form between the amino acid and the tRNA molecule
What are the 2 steps that allow proteins to be synthesised and in what order?
- Transcription
- Translation
Definition of Transcription
The production of mRNA from DNA
Where does transcription take place in eukaryotic cells?
Transcription takes place in the nucleus
Where does transcription take place in prokaryotic cells?
Takes place in the cytoplasm
What are the first 2 steps of transcription?
1)DNA Helicase begins to unwind the DNA, exposing some the bases (which breaks H bonds)
2) Free RNA nucleotides associate with their exposed complementary bases on the antisense strand of the unwound DNA by H bonding. RNA polymerase adds each nucleotide to the mRNA polynucleotide chain by forming a phosphodiester bonds
What are the last 2 steps of Transcription?
3) Once the RNA polymerase has passed by, H bonds between the uncoiled strands of DNA reform. The strands recoil into a double helix.
4) When RNA polymerase reaches a stop triplet code, it detaches from DNA and production of mRNA is complete
What are the steps in gene splicing?
Introns are removed and exons are spliced together. This forms mature mRNA which is ready for translation by ribosomes. This occurs in the nucleus and the mature mRNA leaves through nuclear pores
Definition of Translation
The production of polypeptides from the sequence of codons carried by mRNA
What are the first 2 steps of Translation?
1) mRNA attaches to a ribosomes and tRNA collects amino acids from the cytoplasm and carries them to the ribosome. tRNA is a single stranded molecule with a binding site at one end thus it can only carry one type of amino acid and a triplet of bases
2) tRNA attaches itself to mRNA by complementary base pairing - 2 molecules attach to mRNA at a time
What are the last 2 steps of Translation?
3) The aa attached to 2 tRNA molecules join by a peptide bond and then tRNA molecules detach themselves from the amino acids, leaving them behind
4) This process is repeated thus leading to the formation of a ppt chain until a stop codon is reached on mRNA and ends the process of protein synthesis
What is a mutation?
They are changes in DNA which arise spontaneously during replication and any change in the base sequence or quantity of DNA is a mutation
What are the 2 key types of mutation?
Substitution and Deletion
How does substitution occur and what does it do?
This is when one nucleotide in the DNA sequence is replaced by another. The effect of the change in a amino acid is dependent on the role of the original aa in the overall shape and function of the protein.
Why may substitution not always be harmful?
Due to the substituted nucleotide may code in that triplet for the same amino acid
How does Deletion occur and what does it do?
A Deletion is when a nucleotide in the DNA sequence is lost. The result of this nucleotide being lost can cause a frame shift. A frame shift is when completely different amino acids are being coded for
What are the 2 forms of mutations that occur in chromosomes?
Polyploidy and Non-disjunction
How does Polyploidy occur and what does it do?
Changes can occur in the whole set of chromosomes so that an individual has 3 of more sets of chromosomes instead of 2
How does Non-disjunction occur and what does it do?
Non - disjunction occurs when chromosomes fail to separate correctly in meiosis. As a result the gametes and zygotes formed will have one more or one less chromosome than they should.
Name a genetic disease which is also a disability caused from non - disjunction
Down syndrome
