How genes work Introduction to genetics

the function of genes provide information needed make molecules called proteins in cells. cells smallest independent parts of organisms: human body contains 100 trillion cells, while small organisms bacteria 1 single cell. cell miniature , complex factory can make parts needed produce copy of itself, happens when cells divide. there simple division of labor in cells—genes give instructions , proteins carry out these instructions, tasks building new copy of cell, or repairing damage. each type of protein specialist 1 job, if cell needs new, must make new protein job. similarly, if cell needs faster or slower before, makes more or less of protein responsible. genes tell cells telling them proteins make , in amounts.

genes expressed being transcribed rna, , rna translated protein.

proteins made of chain of 20 different types of amino acid molecules. chain folds compact shape, rather untidy ball of string. shape of protein determined sequence of amino acids along chain , shape that, in turn, determines protein does. example, proteins have parts of surface match shape of molecule, allowing protein bind molecule tightly. other proteins enzymes, tiny machines alter other molecules.

the information in dna held in sequence of repeating units along dna chain. these units 4 types of nucleotides (a,t,g , c) , sequence of nucleotides stores information in alphabet called genetic code. when gene read cell dna sequence copied similar molecule called rna (this process called transcription). transcription controlled other dna sequences (such promoters), show cell genes are, , control how copied. rna copy made gene fed through structure called ribosome, translates sequence of nucleotides in rna correct sequence of amino acids , joins these amino acids make complete protein chain. new protein folds active form. process of moving information language of rna language of amino acids called translation.

dna replication. dna unwound , nucleotides matched make 2 new strands.

if sequence of nucleotides in gene changes, sequence of amino acids in protein produces may change—if part of gene deleted, protein produced shorter , may not work more. reason why different alleles of gene can have different effects in organism. example, hair color depends on how of dark substance called melanin put hair grows. if person has normal set of genes involved in making melanin, make proteins needed , grow dark hair. however, if alleles particular protein have different sequences , produce proteins can t jobs, no melanin produced , person has white skin , hair (albinism).

genes copied

genes copied each time cell divides 2 new cells. process copies dna called dna replication. through similar process child inherits genes parents, when copy mother mixed copy father.

dna can copied , accurately because each piece of dna can direct creation of new copy of information. because dna made of 2 strands pair 2 sides of zipper. nucleotides in center, teeth in zipper, , pair hold 2 strands together. importantly, 4 different sorts of nucleotides different shapes, strands close properly, nucleotide must go opposite t nucleotide, , g opposite c. exact pairing called base pairing.

when dna copied, 2 strands of old dna pulled apart enzymes; pair new nucleotides , close. produces 2 new pieces of dna, each containing 1 strand old dna , 1 newly made strand. process not predictably perfect proteins attach nucleotide while building , cause change in sequence of gene. these changes in dna sequence called mutations. mutations produce new alleles of genes. these changes stop functioning of gene or make serve advantageous function, such melanin genes discussed above. these mutations , effects on traits of organisms 1 of causes of evolution.