Chapter 9 Flashcards
how is genetic info
- stored
- replicated
- translated
DNA characteristics
- carries a large amount of info
- it can be accurately copied
- is stable under a range of environmental conditions
- the info it carries is used code for amino acid sequences
structure of dna
DNA is a type of nucleic acid polymers made from nucleotides nucelotide are conposed of three parts: 1. 5 carbon sugar 2. phosphate group 3. nitrogen base (variable structure)
sugars
the sugar of one nucleotide bond to the phosphate of another nucleotide
the sugar and phosphate always have the same chemical structure
in DNA there are 4 possibel nitrogen bases
Adenine (A) thymine (T) cytosine (C) guanine (G) the sequence of nitrogen babes is a source of info
DNA normally exists
as two separate strands
each strand runs in opposite directions
hydrogen bond form
between the nitrogen bases of the strands
cytosine only bonds with guanine
adenine only bonds with thymine -complimentary pairing
double strands of DNA are
twisted around one another into double helix
DNA replication
one strand of DNA acts as a template for the construction of a new strand
- double strands of DNA are pulled apart
- complimentry nucleotides are synthesized into new DNA strands
- hydrogen bonds re-form between nitrogen bases
semi conservation replication
each new set of double DNA strands contains an old strand
enzymes are responsible for
the 1st two stages of replication
responsible for each phase of replication
DNA helicase
breaks hydrogen bonds between double strands
moves in one direction only
DNA ploymerse
joins nucleotides together in their proper sequence by reading the sequence of the original strand
can only snythesize new strands in one direction
requires a primer (short sequence of nucleotides) to start a new DNA strand
one strand is made continuously, the othe ris made in sections
DNA ligase
join strands of DNA together
the new strands run in opposite direction to the old strands
another type of nuclecic acid
RNA (ribonucleic acid)
structure
similar to DNA except:
1. the 5 carbon sugar is different
2. thymine is not present, it is replaced by uricil (U) it goes with adenine
3. does not necessarily form a double strand
it can also act as an enzyme
protien synthesis (how genetic info is used)
DNA codes for amino acid sequences
4 different nitrogen babes in DNA code for 20 different amino acids in protiens
groups of three babes (codons) code for a single amino acid
how many different combinations are there
64 different possible combinations of 3 nucleotide bases
some base combinations code for the same amino acid
2 stages of protien synthesis
transcription
translation
transscription
copying of one DNA strand into an RNA strand
translation
coverting RNA sequence into an amino acid sequence
invloved in transciption
takes places in the the nucleus
promotor: DNA sequence where transcription starts
terminator: DNA seqeuence where transciption ends
RNA polymerase: emzyme that carries out transsciption
steps in transciption
- initation- RNA polymerase attaches to DNA at the promoter
- DNA strands are pulled apart
- elongation- RNA nucleotides are bonded together based on the DNA sequence
- termination- transciption occurs until a terminator sequence occurs until a terminator sequence is encountered
at the terminator the RNA polymerse detaches from the DNA and releases the RNA strand
the resulting RNA strand is known as messenger RNA or mRNA
involved in translation
occurs in the cytoplasm on ribosomes
aligns mRNA and transfer RNA
have two binding sites for tRNA molecules
transfer RNA (tRNA)
two attachment sites:
1. amino acid attachment site
2. aticodon- a set of three nucleotides complimentry to mRNA
the type of amnio acid attached to a tRNA depends on its anticodon sequence
steps in translation
- ribosome and tRNA bind together. This always occurs at the nucleotide sequence (the start codon)
- a 2nd tRNA molecule binds to the 2nd binding site of the ribosome
- the amino acid from the first tRNA is removed from the tRNA and bonded to the amino acid on the second tRNA
- the first tRNA is released from the ribosome
- the second tRNA is shifted from the second to the first binding site
- the process is repeated until a stop codon seqeunce is reached
- thr amino acid sequence is released from the final tRNA
genes
can be considered sections of DNA
they are always located int he same region of a chromosome
genes arent necessarily a easily defined sections of DNA
alleles
make protiens that preform the same function but have different DNA code
in ekaryotes there are additional steps in transciption
not all DNA codes for protiens- exons do, introns do not
initially all sections are copied
before mRNA leaves the nucleus introns are removed and the remaining sections joined
more than one protien can be made from a section of DNA by splicing different sections of mRNA together
