DNA Flashcards
who discovered dna
watson and crick in 1953
but rosalind franklin worked out the structure
what does DNA stand for
deoxyribose nucleic acid
DNA is a polymer, what is a polymer
long chain of molecules made of the same units
what are the individual units of DNA
nucleotides
what is a single nucleotide made up of in DNA
phosphate, deoxyribose (pentose) sugar and a nitrogenous base
how are nucleotides joined together
in a condensation reaction
what bonds do sugar and phosphate form when nucleotides join together
phosphodiester bond
what are the 4 bases (complimentary pairs)
adenine and thymine
guanine and cytosine
what are the bases made up of
rings of carbon and nitrogen
what is a purine and which bases are purines
double rings
guanine and adenine
what is a pyrimidine and which bases are pyrimidines
single rings
cytosine and thymine
a purine always pairs……
with a pyrimidine
what is synthesis
making something
what is replicating
copying somethig
what do nitrogen bases act like
oxygen in what making the bases polar which allows hydrogen bonds to form
are the hydrogen bonds formed weak or strong and why
weak
essential for replication
what is DNA replication
chromosomes must make copies of themselves so that when cells divide each daughter cell receives an exact copy
what is protein synthesis
the sequence of bases represents the information carried in DNA and determines the sequence of amino acids in a protein
what are the 3 theories of DNA replication
conservative
semi conservative
dispersive
what is conservative theory
the original DNA is completely conserved and a whole new copy is created
what is semi conservative theory
one strand of the original goes to each daughter strand and one copy strand
what is dispersive theory
the original is fragmented and is split between the copies
what is the DNA replication process
1) helicase enzyme breaks the hydrogen bonds and the DNA unzips
2) free nucleotides bond to both DNA strands by complimentary base pairing
3) DNA polymerase enzymes joins the nucleotides between the sugar and phosphate groups
4) this results in two identical double stranded molecules
what did meselson and stahl do
devised an experiment to deduce which was the correct theory
how did meselson and stahl conduct their experiment
1 - e coli were grown for several generations in a medium with N-15 present
2 - the n 15 e coli were transferred to a n14 medium to allow the e coli to divide
3- dna was extracted periodically and compared to the density of a pure sample of n14 and n15, they used a centrifuge to compare densities
what is the correct DNA replication theory
semi conservative
what is the function of DNA
contains the instructions for protein synthesis
what are codons
the section of a molecule that codes for one amino acid (in mRNA)
what did NIRENBERG discover
that there was 4 bases and 20 possible amino acids
so said that there codons must be at least 3 bases long
what is the triplet code
three bases code for one amino acid
there are at least 64 possible codons
but only 20 amino acids
3 of the codons are stop codons which ends protein synthesis
what is a redundant code
many of the amino acids are coded for by more than one code so the ones that aren’t used are described as redundant or degenerate
what is non overlapping
when you convert DNA into an amino acid sequence you more along three bases each time you read a codon
why is the genetic code described as the universal code
all living organisms use the same 4 bases and the same codons for the same amino acids
what are exons
the section of a gene that code for one amino acid
what are introns
sections f DNA in the gene that DO NOT code for amino acids so they need to be removed before it can be translated
what does RNA stand for
ribose nucleic acid
what does RNA consist of
phosphate, ribose sugar and nitrogenous bases
list three difference between RNA and DNA
RNA- single stranded contains uracil ribose sugar DNA- double stranded contains thymine deoxyribose sugar
what are the three types of RNA molecules
rRNA ribosomal rna
mRNA messenger rna
tRNA transfer rna
what is stage 1 of protein syntheiss
transcription
describe transcription
1- helicase enzyme breaks the hydrogen bonds in the DNA where the gene is so the DNA unwinds
2 - free RNA nucleotides line up against the DNA template strand by complimentary base pairing
3 - RNA polymerase moves along the molecule joining the nucleotides in a condensation reaction to form the phosphodiester bond
4 - the mRNA molecules detaches from the DNA
5 - the DNA reforms as a double helix
6 - the mRNA leaves the nucleus through a nuclear pore
what is stage 2 of protein synthesis
translation
describe translation
1 - a ribsome attaches to the start codon of the mRNA
2 - a tRNA binds with its specific amino acid as determined by the anti codon
3 - the tRNA binds to the mRNA
4 - a second tRNA binds to the next mRNA codon bringing its amino acid
5 - a peptide bonds forms between the adjacent amino acids
6 - the ribosome move along the mRNA the new tRNAs bind to the mRNA and a polypeptide chain is formed until a stop codon is reached
describe the structure of tRNA
single stranded
has hydrogen bonds which form between complimentary base pairs
has three bases which are anti codon
has an amino acid bonding site
what is the one gene one polypeptide theory
each gene is a sequence of nucleotides that are translated into a chain of amino acids which form a polypeptide
polypeptides need modifying to become functional proteins
this means that polypeptide sequences of one gene might produce more than one protein
why do we need cells to divide
mitosis - cell growth, replacement and asexual reproduction
meiosis - sexual reproduction
what does the cell cycle consist of
interphase and mitosis and cytokinesis
how much of the cell cycle does interphase take up
about 90%
what is interphase
the phase between division
what happens during interphase
the DNA is unwound as chromatin so the genes are accessible for transcription
the cell is metabolically active
cell growth and DNA replication
what are the three sections of interphase
G1,G2 AND S phase
what happens during G1+G2
cell growth
new protein synthesis and new organelles produced
what happens during S phase
dna replication
to form two identical sister chromatids
what are the four sections of mitosis
prophase, metaphase, anaphase and telophase
what happens during prophase
preparation
chromatids condense
nucleolus disappears
nuclear envelope starts breaking own
spindle apparatus forms
centrioles migrate to the poles of the cll
chromatids combine with HISTONE to become shorter and thicker
what happens during metaphase
nuclear membrane has broken down
chromosomes align in the centre of the cell
each chromosome is attached to a spindle fibre by its centromere
what happens during anaphase
centromere of each chromatin splits
one chromosome from each chromatid moves to centrioles at poles of cells
the chromatid which are now separate are chromsomes
what happens during telophase
nnuclear membrane forms around each group of newly divided chromosomes
nucleolus reforms
spindle disappears
chromosomes extend into chromatin becoming ‘invisible’
what is cytokinesis
the cytoplasmic division of other materials (cytoplasm, cell membrane and other organelles)
what does cytokinesis result in
the formations of two new daughter cells
What are the two energy laws
Energy cannot be created or destroyed
Energy can be transferred from one form to another
Why do we need energy
Muscular contraction Active transport Growth Thermoregulation Catabolism
What is bioluminescence
Converting chemical energy into light energy
What does ATP stand for
Adenosine triphosphate
What is ATP made up of
Adenine
Ribose
3 phosphate groups
Adenine + ribose =
Adenosine
What is the role of ATP
short term energy store of the cell
Often called the energy currency because it picks up energy from food in respiration and passes it on to power cell processes
What are the advantages of ATP
Small Soluble Universal Quick Releases energy in small amount when and where it's needed
What is ATPase
The enzyme that removes the end phosphate groups one at a time
What does breaking bonds require
Energy
How much energy is needed in the case of ATPase to break a bond
A small amount
What is the equation for the breaking down of ATP
ATP—-> ADP + Pi
What happens to the Pi bonds and how much energy does it release
Bonds with water and becomes hydrated
Releases more energy than was required to split ATP
What is the net energy release when ATP is broken down
30.6 KJ mol^-1
What is phosphorylation
The addition of phosphate to ADP
What is cancer
A breakdown in the cellular control mechanism that slows down cell division
Cells that should be stable begin to divide forming a tumour
What is a tumour
A swelling that can occur almost anywhere in the body
A MASS OF ABNORMAL CELLS THAT DIVIDE UNCONTROLLABLY
What are malignant tumours
Destroys the surrounding tissue and their cells can break away and spread through the BLOOD AND LYMPH into other sites where they form secondary tumours
What are benign tumours
grow very large but don’t destroy the surrounding tissue
Why is cancer so dangerous
Tumours interfere with the activity of cells in the tissues if the organs that surround them
Why are benign tumours dangerous
Can compress tissues preventing normal blood flow or nerve function
Why are malignant tumours so dangerous
Invade surrounding tissues and kill normal cells
How can you control the division of cells
PROTO-ONCOGENES regulate cell growth and differentiation but if they mutate can become ONCOGENES (form cancer)
TUMOUR SUPPRESSOR GENES inhibit the cell cycle for instance if DNA is damaged
Can mutate and lead to cancer
What is a haploid cell
Has half the number of chromosomes of a normal body/semantic cell
What are homologous chromosomes
Have the same structural features and patterns of genes
What does independent assortment help to do
Increase variation
What is different about meiosis compared to mitosis
In meiosis it has two stages of pro,met, ana and telo phase
