4.1 DNA, genes and chromosomes

what is a gene

sequence of DNA bases that codes for a polypeptide

DNA in prokaryotic cells

-short

-circular

-not associated with proteins

DNA in eukaryotic cells

-long

-liner

-associated with proteins called histones

DNA in mitochondria and chloroplasts

-short

-circular

-not associated with proteins

how many different amino acids occur in a protein

20

what bases are present in a DNA

Adenine

Thymine

Guanine

Cytosine

what does degenerate code mean

amino acid is coded for by more than one triplet

what does non-overlapping code mean

each base is only read once

what does universal code mean

triplet codes for the same amino acid in all organisms

what is each thread of chromosomes called

chromatid

what is dna in chromosomes held by

histones

what are chromosomes made out of

dna and proteins

why is dna wound around histones

to fix it in the position

why is DNA-histone complex coiled, looped and further coiled before being packed into a chromosome

so more dna is condensed in 1 chromosome

where are genes located on DNA

along DNA’s length

how many DNA does 1 chromosome contain

one

what is locus

position of a gene on dna

what is homologous chromosomes

a pair of chromosomes, one maternal and one paternal, that have the same gene loci and therefore determine the same features

in terms of genes what do homologous pairs carry

the same gene but not necessarily the same alleles of genes

what happens when parents have different alleles of a gene in terms of amino acids

each allele has a different base sequence, therefore a different amino acid sequence, so produces a different polypeptide

what changes in the base sequence of a gene lead to

new allele is produced (mutation) and results in a different sequence of amino acids being coded for

different polypeptide is produced

so a different protein

why is RNA needed

protein synthesis

how does DNA move to the cytoplasm for protein synthesis from the nucleus

sections of DNA code are transcribed onto a RNA

what does mRNA do

transfers DNA code from nucleus to the cytoplasm

why can mRNA transfer DNA to the cytoplasm

it is small enough to leave the nucleus through the pores

what is structure of RNA

-single strand

-pentose sugar ribose

-one of the bases: A,G,C,U

-phosphate group

what is base sequence of mRNA is determined by

sequence of bases on a length of DNA in a transcription

what does mRNA act as

template for protein synthesis

what part of tRNA does amino acid easily attach to

where one end of the chain extends over the other

what is on the opposite side of tRNA to the point of amino acid attachment

sequence of 3 other organic bases (anticodon)

why does each tRNA have an anticodon specific to an amino acid

because that tRNA is specific to that amino acid