DNA, genes and chromosomes

what are the difference between prokaryotic and eukaryotic DNA?

Eukaryotic - nucleus, sphere, introns, larger, linear, proteins to form chromosomes (histones)

Prokaryotic - nucleoid and plasmids, continuous loop or pellet, no introns, smaller, circular, no proteins, no chromosomes

chromosome structure?

• sister chromatid - 1

• centromere - 1

• polynucleotide chain - 2

• Only visible as an ‘X’ when dividing

• First visible - start of cell where they are two threads

• DNA held by histones

• Humans - 46

• Dogs - 78

how is DNA arranged within a chromosome?

• DNA molecule, DNA-histone complex, coiled, forms loops, pack together, forms chromosome

• Tightly coiled

what is a homologous chromosome?

• pairs of chromosomes

• one is maternal and one is paternal

• contain the same genes in the same loci

• not genetically identical

• Different alleles

• Total - diploid

• Half - haploid

What is mutation?

Changes in the base sequence of a gene that produces a new allele of that gene

different amino acid sequence is coded

different polypeptide and protein

may not function properly

Enzyme - different shape on active site so may not fit substrate

What is an allele?

Different form of the same gene

individual’s inherit one allele from each parent

Alleles has different base sequence, different amino acid sequence, different polypeptide

What is a gene?

Section of DNA contains coded information for making polypeptides and functional RNA

Coded information - specific base sequence on DNA

Locus - specific position of a gene on DNA

What is the genetic code?

3 bases (triplet) that codes for one specific amino acid

20 different amino acids

4 bases

64 different codes so satisfys the needs of 20 amino acids

What are features of the genetic code?

Degenerate - most amino acids are coded for by more than one triplet

Stop codes - Three triplets do not code for an amino acid

Non-overlapping - each base in the sequence is only apart of one triplet

Universal - when each triplet codes for the same amino acid in all organisms

Introns - no coding

Exons - expressed/coding

What is Polypeptide synthesis?

DNA provides instructions in the form of a long sequence of bases

Complementary part of the sequence is made in the form of pre-mRNA vis transcription

Pre-mRNA is spliced to form mRNA

mRNA is a template for complementary tRNA to attach and the amino acids link to make a polypeptide via translation

What is transcription?

DNA helicase breaks hydrogen bonds

Complementary activated free RNA nucleotide

Binds to template strand

RNA polymerase phosphodiester bonds adjacent

Pre-mRNA spliceosome introns

Mature mRNA diffuses out of nuclear pore

What is translation?

mRNA associates with ribosome

First two codons attract complementary tRNA

complementary base pairing forms hydrogen bonds between mRNA codons

Peptide bonds between two amino acids catalysed peptidyl transferase and hydrolysis ATP

Moved forward one codon

1st tRNA leaves and new tRNA and carries amino acid to 3rd codon sequence

Peptide bonds between 2nd and forms dipeptide

Ribosome moves until stop codon detaches due to release factor

Polypeptide chain released folds to right shape

what is the genome?

complete set of genes in a cell

what is the proteome?

the complete set of proteins a cell is able to produce.

what is RNA?

• ribonucleic acid

• where sections of DNA are transcribed onto a single stranded RNA.

• this is to synthesise proteins in the cytoplasm from the sequence of amino acids in the DNA.

• mRNA - messenger RNA

• tRNA - transfer RNA

what is the RNA structure?

• polymer

• made from repeating mononucleotide sub units

• pentose sugar ribose

• one nitrogenous bases: adenine, cytosine, guanine, uracil.

• a phosphate group.

what is mRNA?

• transfers the DNA code from nucleus to cytoplasm.

• leaves via nuclear pores.

Differences between DNA, mRNA and tRNA.

DNA -

mRNA -

tRNA -