Topic 4: Genetics biodiversity and classification DNA Flashcards
Define Gene
A section of Dna that contains a code for making a polypeptide and funcitonal RNA. the code is a specific sequence of bases (amino acids).
polypeptides make proteins and so genes determine the proteins of an organism
Define Allele
different versions of the sae gene found at the same locus on a chromosome
Define Chromosome
in a eukaryotic cell nucleus dna is stored as chromosomes.
humans have 23 pairs or 46 in total
(one arm chromatid)
(centromere centre)
23rd pair x and y sex chromosomes (human karyotype)
what is a homologous pair
a hmoglous pair of chromosomes are exactly the same size, have the same genes but might have different alleles
How is DNA stored in eukaryotes
DNA is stored as chromosomes inside of the nucleus
chromosomes are in linear shape/
to tightly coil the DNA to fit in the nucleus as chromosomes, the DNA is tightly wound around proteins called histones.
the complex on DNA wrapped around a hsitone is called a nucleusome
mitrochondria and chloroplasts contain prokaryotic-like DNA (because the are centre of reactions. DNA encodes for enzymes of reactions)
How is DNA stored in a prokaryotic cell
prokaryotes also carry DNA in chromosomes, But the DNA molecules are short and circular the DNA is not wound around histones instead it supercoils to fit it
Describe the prokaryotic like DNA in mitrochondria and chloroplast
similar to prokaryotic cells because its circular short and not histone bound.
mitrochondria and chloroplasts contain prokaryotic-like DNA (because the are centre of reactions. DNA encodes for enzymes of reactions)
What are the three components of nucelotides
pentose sugar phosphate group and an organic base
describe the structure of DNA
made up of deoxyribose sugar phosphate group on one of four rganic bases (A C G T) double stranded with hydrogen bonds between bases to form a helix shape
What are the three features of the genetic code
-
degenerate- more than one triplet codes for the same amino acid (64 possible triplets for 20 amino acids)
2.** universal-**same bases and sequences used by all species - non overlapping each triplet is only read once
What is genetic code
The order of bases on DNA consits of codons (triplets of bases that code for a particualr amno acid)
Describe the start and stop codon
At the start of every gene there is a ‘start codon’ TAC in DNA or AUG in mRNA it encodes for the amino acid methionine which is later removed from the protein if unecessary for the structure.
Stop codons- at the end of ever gene there are 3 bases that do not code for an amino acid these stop codons mark the end of a polypeptide chain ND CAUSE RIBOSOMES TO DETACH AND STOP TRANSLATION ATT ATC and ACT on DNA
Describe how genetic code is degenerate
There are 20 amino acids that the genetic code has to be able to code for. there are four DNA bases (CGTA) and therefore three bases are needed to make enough comibinations to code for at least 20 amino acids.
The genetic code is degenerate because multiple codons (sequences of three bases) can code for the same amino acid.
4N 43=64codons→enough/more than.
this is an advantage as if a mutation occurs and codons will be different it may still code for the same amino acid and have no effect
Describe how genetic code is universal
the same triplet of bases codes for the same amino acid in all organisms.
this is an advantage as it means genetic engineering is possible. e.g inserting the human gene for insulin into bacteria
Describe how genetic coade is non overlapping
each base in a gene is only part of one triplet of baes that codes for one amino acid. therefore each codon or triplet bases is read as a discrete unit.
this is an advantage as if a point mutation occurs it will only affect one codon, and there fore one amino acid
What are exons and introns
introns are sections of DNA that do not code for amino acids and thereofre polypeptide chains. they are found in eukayotic dna but not prokaryotic. these get removed, spliced out of Mrna molecules. foud between exons within genes
exons are sections that do encode for amino acids. separated by one or more introns. fo
What is the genome and proteome
The genome is an organisms complete set of DNA in one cell. where as the proteome is the full range of proteins in one cell.
genome never changes and proteome constantly changes
Descrive the function of RNA
the function of RNA is to copy and transfer the genetic code/info from DNA in the nucleus to the ribosomes. some RNA is also combined with proteins to create ribosomes for protein synthesis
What is RNA structure
RNA is a polymer of a nucleotide formed of a ribose sugar , a nitrogenous base and a phosphate group. The bases are adenine guanine cytosine and urcail. relatively short polynucelotide chain and it is single stranded
What are the three types of RNA
mRNA
tRNA
rRNA
Describe the structure of mRNA
Messenger RNA is a copy of a gene from DNA
mRNA is created in the nucleur and leaves the nucleus to carry the copy of the genetic code of one gene to a ribosome in the cytoplasm
Suggest advantages of using mRna rather than DNA for translation
shorter and contains uracil which breaks down quickly so no excess polypeptide forms.
short lived as it is only needed temporarily to help create a protein, by the time any enzymes could break it down it would have already carried out its function.
contains no introns
linear- ribosomes move along strand and tRNA bins to exposed bases
single stranded and every 3 bases in the sequenece codes for a specific amino acids
Describe the structure of transfer RNA (tRNA)
a single strand of around 80 nucleotides that is folded over into a clover shape held in place by H bonds. one end is an anti codon on the opposite end is an amino acid binding site.
anti codons are complementary to codon on mRNA
