DNA, genes, alleles and RNA Flashcards
How is DNA stored in eukaryotic cells?
As chromosomes where the polynucleotide chain is wound up around histone proteins to form nucleosome
In the nucleus
Where else in a eukaryotic cell is DNA found?
In mitochondria
In chloroplasts (if a plant cell)
Features of eukaryotic nucleic DNA
Very long
Linear
Associated with proteins
DNA is only visible when it has condensed in mitosis otherwise exists as chromatin
Features of DNA in chloroplasts/ mitochondria
Shorter molecule
Circular: no free ends
Not bound to histone proteins
How is DNA stored in prokaryotic cells?
Found freely in the cytoplasm as long loops of DNA (additional plasmid loops)
Features of DNA in prokaryotic cells
Shorter molecule
Circular: no free ends
Not bound to histone proteins
+ additional circular loops of plasmids
What is a gene?
A base sequence in a section of DNA that codes for either:
-The amino acid sequence of polypeptide
-A functional RNA eg tRNA or rRNA
How does the gene determine the protein?
The sequence of bases in a gene determines the transcribed mRNA (complementary base pairings) which in protein synthesis determines the amino acid sequence (primary structure). This determines tertiary structure based on bonds between R groups
Genome
Complete set of genes in a cell inc mitochondrial and chloroplast DNA
Proteome
Full range of proteins a cell is able to produce
Cell proteome
The set of proteins produced by a specific cell as a result of which genes are turned on and off
Allele
An alternative version of the same gene
May possess a different nucleotide base sequence which alters the polypeptide encoded for by a gene
where are genes/ alleles located on a chromosome?
On the same gene locus in the chromosome
Homologous pair of chromosomes
Chromosomes that possess the same genes at the same gene loci: may or may not have the same alleles (therefore could potentially be a difference in nucleotide base pair)
What is each chromosome in a homologous pair?
Maternal (from mother’s female gamete)
Paternal (from father’s male gamete)
What do alleles at a fixed position encode for in a homologous pair?
The same characteristic or protein (eg hair colour, eye colour etc) but different variations eg black, brown etc
2 Types of RNA
Messenger RNA (mRNA)
Transfer RNA (tRNA)
Function of messenger RNA
Carries genetic code of DNA, to ribosomes in order to synthesise the polypeptide that the base sequence encodes for
Structure of mRNA
Formed from condensation of RNA nucleotides to form phosphodiester bonds between each
Ribose sugar
Nucleotide bases: Adenine, Uracil, Cytosine, Guanine
Single polynucleotide strand = single helix molecule
Function of tRNA
Carries the amino acids used to synthesise a polypeptide chain during translation
Structure of tRNA
Single polynucleotide strand folded into clover shape: hydrogen bonds between complementary base pairs to hold it together
Has amino acid binding site at one end
Has 3 bases at other end known as anticodon
mRNA vs tRNA structural differences
mRNA has codons, tRNA has anticodons
mRNA is linear, tRNA is clover leaf shape (same point as H bonds)
mRNA does not have an amino acid binding site but tRNA does
mRNA has more nucleotides than tRNA does
Similarities between prokaryotic dna vs eukaryotic dna
Both contain phosphodiester bonds in the dna molecule
Both have the same nucleotide structure: phosphate, deoxyribose sugar and nucleotide base
Differences between prokaryotic dna vs eukaryotic dna
Prokaryotic is circular eukaryotic is linear
Prokaryotic is not associated with histone proteins but eukaryotic is associated with histone proteins
Prokaryote has no plasmids but eukaryote does
Prokaryote has no introns but eukaryote has introns
