DNA and Genes

3.2.2 You should know:

Of evidence for the semi-conservative model for replication of DNA

That a gene occupies a locus on a particular strand of DNAThat genes contain a code as a specific sequence of bases

to determine a polypeptideHow DNA is organised for both eukaryotic and prokaryotic

cells.A sequence of three bases (triplet) denotes 1 amino acidThe base sequence of a gene determines the amino acid

sequence in a polypeptide.Not all DNA codes for polypeptidesHow Wales is contributing to the global pool of genomic

research.

DNA

structure

replication

Genes and chromosomes

Choose 12 answers from the list below and write into your bingo card.

helicase identical 40%antiparallel 20% semiconservative DNA polymerase deoxyribose cytosineTAG double helix phosphate GGC bases nucleotides hydrogenCrick and Watson

N14N15 1st Generation 2nd generation

Results-centrifuged DNA samples from E.coli bacteria

http://highered.mcgraw-hill.com/sites/007337797x/student_view0/chapter12/animation_quiz_-_meselson_and_stahl_experiment.html

A gene

A gene is a section of DNA which holds the genetic information to instruct a cell how to build one poly peptide chain.

Each gene codes for a polypeptide chain which could be an enzyme or part of a larger protein molecule.

sph.bu.edu

A reminder of protein structure.

Remember the primary structure is the key to the other levels

Genes

One-gene-one-enzyme theory Production of a given peptide is under control of a

single gene

Genes and proteins

The nucleus acts as the control centre of a cell because the DNA it contains govern the production of enzymes for the cell and thereby which reactions can take place.

Genes work in pairsGenes can exist in different forms called

alleles

A locus

The position a gene holds on a chromosome is its locus

Cell type Nature of DNA

Prokaryotic The DNA molecules are:

They are not chromosomes.Eukaryotic The DNA molecules are:

They are called chromosomes

DNA in cells

Chromosome structure

DNADouble

stranded, coiled molecule

The genetic code

A triplet of bases codes for one amino acidDNA is used to build up a copy as RNARNA can leave the nucleus and join with a

ribosomeThe information is interpreted and used to

build a polypeptide chain

Introns and exons

multiple repeats-

These are DNA sequences that repeat over and over. E.g. CCTTCCTTCCTT. They are found inbetween genes. These areas don’t code for amino acids either.

Alleles

Alternative forms of a geneGenes work in pairs

If a new allele arises due to a change in BASE sequence it is called a mutation

Not all mutations are harmful but sometimes the poly peptide formed cannot fold correctly so has an altered shape and becomes non functional

Suggested viewing:

•Meselsohn and Stahl animation MCGrawHillhttp://highered.mcgraw-hill.com/sites/007337797x/student_view0/chapter12/animation_quiz_-_meselson_and_stahl_experiment.html

•How DNA is packaged(basic) DNA learning centerhttp://www.youtube.com/watch?v=9kQpYdCnU14