2.1.3 Nucleotides and nucleic acids Flashcards
1
Q
what are nucleotides + what it consists of
A
- biological molecules that participate in nearly all biochemical processes
- consist of a pentose sugar molecule to which is attached a phosphate group and an organic nitrogenous base
- form monomers of nucleic acids
2
Q
what causes nucleotides to link and form polymers called polynucleotides
A
- condensation reactions
- nucleotides are joined together by phosphodiester bonds
> phosphate group of one nucleotides forms a phosphodiester bond with sugar molecule of another nucleotides
3
Q
what are the 4 different organic nitrogenous bases
A
- adenine
- thymine
- cytosine
- guanine
4
Q
what are the two different types of organic nitrogenous bases + differences
A
- purines = larger bases containing 2 carbon rings
> adenine + guanine - pyrimidines = smaller bases containing 1 carbon ring
> cytosine + thymine + uracil - remember purines always pair with pyrimidines
5
Q
what are the bonds between the organic nitrogenous bases + how many
A
- hydrogen bonds
- A + T have 2 bonds
- C + G have 3 bonds
6
Q
what are the 2 nucleic acids
A
- DNA (deoxyribonucleic acid)
- RNA (ribonucleic acid)
> both are polynucleotides
7
Q
what are some structural differences in DNA + RNA
A
- DNA has deoxyribose sugar + RNA has ribose sugar
- RNA has base uracil instead of thymine
- RNA polymers are smaller + so can leave nucleus
8
Q
What is the importance of hydrogen bonds in nucleic acids
A
- hydrogen bonds are weak enough so can be easily broken to allow DNA molecule to be opened up
> unzip for transcription + replication
> however they’re strong enough to hold the molecule close together + keep structure intact
9
Q
describe the structure of DNA
A
- polymer consisting of 2 antiparallel polynucleotide chains held together by hydrogen bonds + coiled into helix structure
> DNA molecules are long + carry a lot of encoded genetic information
10
Q
where is DNA found
A
- in the nuclei of all eukaryotic cells
11
Q
how is DNA organised in eukaryotic cells
A
- large molecules of DNA are tightly wound around histone proteins into chromosomes
> each chromosome is a molecule of DNA
> loop of DNA without histone inside mitochondria + chloroplast
12
Q
how is DNA organised in prokaryotic cells
A
- DNA is in a loop within the cytoplasm, not enclosed in a nucleus
- not wound around histone proteins and describes as ‘naked’
13
Q
name the 3 different types of RNA
A
- mRNA (messenger) = made in nucleus, travels to cytoplasm
- tRNA (transfer) = cytoplasm
- rRNA (ribosomal) = in ribosomes which can be free in cytoplasm or attached to RER
14
Q
what is ATP
A
- the universal energy currency of all living organism
> provide energy for chemical reactions in the cells
15
Q
what are phosphorylated nucleotides
A
- ATP + ADP
- comprise of ribose, adenine and inorganic phosphate groups
- they’re energy storage molecules where energy can be released by breaking the phosphate bond between phosphates to release energy
16
Q
how are polynucleotides synthesised and broken
A
- by forming phosphodiester bonds or by breaking them
17
Q
how is the structure of DNA suited for its function
A
- long
- sequence of bases is genetic code
- complimentary base pairing
- double helix to make it more compact
- hydrogen bonds are weak to break apart for transcription but strong to hold structure
18
Q
when in the cell cycle does DNA replication happen + why
A
- in the S phase of interphase
> copying of DNA so that the following cell division each new cells will have the full copy of the original DNA —> semi conservative
19
Q
what is the importance of DNA replication
A
- essential for DNA to be copied to be identical to accurately conserve the genetic information
20
Q
what are mutations
A
- during DNA replication occasionally there will be random and spontaneous changes in the sequence of bases in DNA
> can alter sequence of amino acids and therefore produce abnormal protein
21
Q
what is semi-conservative replication
A
- the idea that when DNA is replicated the new molecule contains one parent strand and one new strand
22
Q
describe the steps in DNA replication
A
- DNA helix unwinds (gyrase enzyme)
- hydrogen bonds between nucleotide bases are broken + catalysed by DNA helicase to unzip DNA and expose bases
> 2 single strands of DNA - each strand acts as template + free DNA nucleotide bases pair with unpaired complimentary base
- phosphodiester bonds form between phosphate of one nucleotide and sugar of another
- DNA polymerase enzyme joins sugar phosphate backbone + hydrogen bonds made between bases
- strands twist to form double helix
- each new DNA molecule contains one parent strand and one new strand
23
Q
describe the structure of RNA
A
- sugar molecule is ribose
- single stranded polynucleotide chain
24
Q
what is the role of mRNA
A
- made in nucleus during transcription
- carries genetic code from DNA to the cytoplasm where it’s used to make protein in translation
- groups of 3 adjacent bases are called codons
25
what is the structure + role of tRNA
- folded into clover shape as hydrogen bonds between specific bases hold the molecule in this shape
- every tRNA molecule has specific sequence of 3 bases at one end called anticodon
- have an amino acid binding site
- found in cytoplasm + involved in translation
- carries the amino acids that are used to make proteins
26
what is the role of rRNA
- ribosome moves along the mRNA strand during protein synthesis
- rRNA in ribosome helps catalyse the formation of peptide bonds between amino acids
27
what is a gene
- sequence of DNA bases that determine the sequence of amino acids in a polypeptide
> primary structure of a protein
28
what is the genetic code
- DNA contains the genetic code which codes for the synthesis of all polypeptides
> its the sequence of bases that codes for specific amino acids
29
what does each codon code for
- a specific amino acid
30
what is the genome
- the entire sequence of DNA in an organism
31
each gene occupies what
- occupies a specific locus on a chromosome and each chromosome consists of one molecule of DNA
> in between genes are non-coding DNA
32
what does it mean that the genetic code is near universal
- in almost all living organisms the same triplet of DNA bases codes for the same amino acid
33
what does it mean that the genetic code is described as degenerate
- more than one codon can code for the same amino acid
> may reduce effect of mutations as a change in one base of triplet could still result in another base coding for same amino acid
34
what does it mean that the genetic code is described as non-verlapping
- code read from starting at fixed point in groups of 3 bases
35
what are the main features of the genetic code
- triplet code so non-overlapping
- it's degenerate
- has punctuation
- widespread but not universal
36
describe the steps of transcription
- gene unwinds + unzips
- hydrogen bonds broken between nucleotide bases
- one of the strands is used as a template
- free RNA nucleotides pair up with complimentary bases and RNA polymerase catalyses formation of hydrogen bonds between them
- phosphodiester bonds formed as well
- transcription stops at end of the gene
- mRNA detaches from DNA template and leaves nucleus through nuclear pore
37
describe the steps of translation
- mRNA strand attaches to ribosome
- tRNA molecules bring amino acids to the ribosome
- the tRNA anticodon binds to the complimentary codon on the mRNA
> temporary hydrogen bonds are made between them
- as ribosome moves along the length of mRNA, it reads code and when 2 amino acids are adjacent a peptide bond forms between them
- the polypeptide chain continues to grow until it coils up into a protein
38
give the steps to how DNA can be purified and extracted
- grind sample in mortal and pestle = breaks cell walls
- mix sample with detergent = breaks down cell membrane releasing cell contents into solution
- add salt = breaks hydrogen bonds between DNA and water molecules
- add protease enzyme = break down proteins associated with DNA in nuclei
- add layer of alcohol on top of sample = causes DNA to precipitate out of solution
- DNA can be seen as white strands + can be picked up by 'spooling' it onto a glass rod
