Biology: definitions, genetic screening and protein synthesis

chromatin

appearance of a chromosome at interphase, when in an elongated uncoiled state

chromosome

condensed thread of chromatin composed of DNA and protein, located in teh nucleus of eukaryotic cells

homologous chromosomes

chromosome pair which are identical with teh same gene sequence

segregation

seperation of homologous chromosomes, only one chromosome from each pair enters the gamete

heredity

transmission of characteristics from parent to offspring and controlled by a genetic code within the chromosome

gene

unit of heredity, with teh genetic code to form a protein

gene expression

production of a protein using teh genetic code of a gene

non- nuclear DNA

DNA located in teh mitochondrian and chloroplast

role of non nuclear DNA

allows organelles to self replicate

non coding DNA (junk DNA)

DNA which does not code for a protein

roles of non coding DNA

1. used to make DNA rpofiles

2. regulating gene expression (switching genes on and off) at different times and in different places in teh body

karyotype

simple picture which shows the number and appearance of chromosomes in the nucleus of a normal body cell

when is a cell diploid

tehre are 2 setts of chromosomes

autosomes

non gender specific chromosomes

genetic screening

test to establish presence or absence ofabnormal genes

eg of diseases screened by genetic screening

cystic fibrosis - mucous build up in lungs
haemochromatosis - to much iron in the body
albinism - lack of melanin

ethics of genetic screening

may encourage termination of pregnancy
possible impact on asssociation with employers and insurance companies

foetal screening

removing cells from teh amniotic fluid and testing for possible genetic disorders

types of RNA and locations

mRNA - nucleus
tRNA - cytosol
rRNA - ribosome

RNA properties

uracil instead of thymine
ribose sugar
single stranded

protein synthesis: stage 1

nuclear enzymes unwind nuclear DNA and break hydrogen bonds
only one DNA strand is used to make a copy of mRNA

protein synthesis: stage 2 - transcription

RNA nucleotides bond with one DNA strand
RNA polymerase acts as a catalyst to join nucleotides together to make mRNA
genetic code on DNA is transcribed to mRNA which it carries to the ribosome

transcription defn

making mRNA using DNA template

protein synthesis: stage 3 - translation

tRNA bring amino acids to the ribosome
tRNA bonds to teh codons on the mRNA using its anti codons
a sequence of amino acids assemble and bonds by peptide links to form a polypeptide chain
polypeptide folds to function

roles of mRNA

transcribes teh genetic code form DNA
carries the genetic code to the ribosome

roles of tRNA

carries amino acids to the ribosome

binds to its complementary mRNA codons to place amino acids in the correct sequence by translating the genetic code on mRNA

roles of rRNA

holds the mRNA in place
forms the ribosome with protein