Nucleic Acids Flashcards
What are Nucleic Acids?
Polymers made from Nucleotides (2 types = DNA and RNA)
What is DNA?
- DeoxyriboNucleic Acid
- found in all organisms (animals, plants, microorganisms)
- carries genes
- genes = section of DNA that codes for a protein
- all organisms are built of proteins
Building block of DNA?
DNA nucleotide (made of phosphate, deoxyribose sugar, nitrogenous base)
4 types of nucleotides (each has a different base, either Adenine/Thymine/Cytosine/Guanine)
DNA structure?
DNA Double Helix
join nucleotides by condensation reaction between sugar and phosphate to form a polynucleotide
join 2 polynucleotides by hydrogen bond between the bases
A joins with T, C joins with G (complementary base pairing)
produces double strand
then coil double strand into Double Helix
Properties of DNA Structure?
Double Stranded = makes DNA more stable & 2 strands act as templates in semi-conservative replication
Coil into Helix = more compact
Sugar-phosphate backbone = protects bases (bases code for protein)
Hydrogen bonds between bases = weak, so double strand separates more easily for semi-conservative replication
Complementary Base Pairing = ensures identical copies of DNA made by semi-conservative replication
DNA Replication?
occurs in interphase before mitosis & meiosis
occurs by semi-conservative replication
Describe Semi-Conservative Replication?
DNA double strand separate and act as templates, producing 2 identical copies of the DNA, each has half the original strand and half the new strand
Evidence for semi-conservative replication?
Replicating Bacterial DNA in 2 types of Nitrogen Isotopes, 15N and 14N
15N = heavy isotope
14N = light isotope
Nitrogen found in nitrogenous bases of DNA
Bacterial DNA made from 15N will have a Heavy Density
Bacterial DNA made from 14N will have a Light Density
Experiment = Bacterial DNA made of 15N is replicated in an environment of 14N – produces DNA molecules with half 15/half 14 (semi-conservative replication, original strand = 15N & new strand = 14N), therefore, DNA molecule has medium density
What is RNA?
RiboNucleic Acid
2 types (mRNA and tRNA)
mRNA = messenger RNA
tRNA = transfer RNA
both single stranded
both made of RNA Nucleotides (phosphate, ribose sugar, nitrogenous bases - AUCG)
Structure of ATP?
Adenosine Triphosphate
made from 1 adenosine and 3 phosphates
formation: ADP + Pi (+ energy used) = ATP
condensation reaction using ATP Synthase
carries energy in its bonds
breakdown: ATP = ADP + Pi (+ energy released)
hydrolysis reaction using ATP Hydrolase
releases energy from its bonds
What makes ATP a good deliverer of energy?
immediate source = need to only break one bond (plus bond is weak)
manageable source = releases small amount of energy
Uses of ATP (releases energy) in organisms?
protein synthesis
organelle synthesis
DNA replication
cell division (mitosis)
active transport
metabolic reactions
movement
maintaining body temperature
Role of Water in Biology?
found in living organisms = cytoplasm (all organisms), xylem/phloem (in plants), tissue fluid and blood (in animals)
also acts as habitats for living organisms
Functions of water?
- high heat capacity - buffers and controls internal body temperature (thermoregulation)
- large latent heat of vapourisation - provides a cooling effect to maintain internal temperature
- forms strong cohesion between water molecules - allows columns of water to form and move through organisms. Causes surface tension where water meets air.
- an important solvent - metabolic reactions can occur - enables waste and essential molecules to be transported
- it is a metabolite in many metabolic reactions - important in essential processes, such as: ATP synthesis, digestion and protein synthesis
Main role of hydrogen ions?
- buffering the blood
- controlling and altering the PH
Main role of iron ions?
- a component of haemoglobin (transports oxygen)
- Involved in the electron transport chain in respiration
Main role of sodium ions?
- sodium potassium pump
- glucose moving into and out of the cell (ileum)
- Amino acids moving into or out of the cell
- Establishing a nerve impulse
Main role of phosphate ions?
- nucleic acids (DNA+RNA)- strong sugar-phosphate backbone
- ATP - respiration - energy
- phospholipids - important in the membranes of cells
- NAD and NADP in photosynthesis
What is a Gene?
a section of DNA that codes for a protein
made out of intron and exon
intron = non-coding DNA (function e.g. turns gene on or off)
exon = coding DNA (codes for protein)
How does a Gene/Exon code for a Protein?
made out of a sequence of bases
each 3 bases code for 1 amino acid (called triplet code)
therefore,
sequence of bases
determines sequence of triplet codes
which determine the sequence of AAs
= polypeptide chain/primary structure (folds to secondary, then to tertiary/quaternary
Properties of triplet code?
degenerate = each AA has more than one triplet code
non-overlapping = each base is read only once
stop codes = occur at end of sequence – do not code for an AA
How does a mutation lead to a non-functional enzyme?
change in base sequence
change in sequence of triplet codes
change in sequence of AAs
change in primary structure
change in hydrogen/ionic/disulfide bonds
change in tertiary structure (3D shape)
change in active site shape
substrate no longer complementary
can no longer form enzyme-substrate complex
How is a protein assembled?
by transcription and translation
transcription = production of a single stranded complementary copy of a gene (called mRNA)
translation = use sequence of codons on mRNA to assemble protein (tRNA brings in AAs)
DNA vs RNA?
deoxyribose sugar vs ribose sugar
thymine vs uracil
double stranded vs single stranded
one type vs two types (mRNA and tRNA)
What is mRNA?
messenger RNA
single stranded complementary copy of a gene
carries the code for assembling protein (on DNA called triplet code, on mRNA called codon)
What is tRNA?
transfer RNA
single stranded RNA folded over into a ‘clover leaf’ shape (held by hydrogen bonds between the bases)
has an AA attachment site on the top
has 3 specific bases on the bottom (anticodon)
anticodon binds to complementary codons on mRNA
What is Transciption?
occurs in nucleolus of nucleus
producing a single stranded complementary copy of a gene (called mRNA)
DNA is double stranded, 1 strand called coding strand & 1 strand called template strand, the template strand will be used to build mRNA
Transcription process?
DNA Helicase breaks the hydrogen bonds between complementary bases in the gene
the double strand of the gene unwinds
leaves 2 separate strands (1 coding strand and 1 template strand)
complementary RNA nucleotides bind to exposed bases on the template strand
RNA Polymerase joins the sugar-phosphate backbone of the RNA strand
leaves pre-mRNA (contains introns and exons)
the copies of the introns are removed by splicing
leaves mRNA
What is Translation?
takes place on ribosomes of Rough Endoplasmic Reticulum
uses the sequence of codons on the mRNA to assemble the protein (tRNA brings in AAs)
Translation process?
mRNA leaves nucleus via nuclear pore
mRNA attaches to a ribosome
complementary tRNA carrying specific AAs bind to the codons on mRNA via their anticodon
the AAs on the tRNA are joined by peptide bonds
What does Meiosis produce?
4 genetically different cells, haploid (half the amount of chromosome/DNA)
Benefits of Meiosis?
produces gametes which will be used in sexual reproduction in animals & plants (2 gametes fuse to form a zygote, zygote develops into organisms)
Stages of Meiosis?
Interphase/Meiosis I/Meiosis II/Cytokinesis
Interphase?
G1: protein synthesis
S: DNA replication (doubles set of DNA)
G2: organelle synthesis
Meiosis I?
Prophase I: DNA coils to form chromosomes, nucleus breaksdown, spindle fibres form, crossing over occurs
Metaphase I: homologous pair of chromosomes line up in middle of cell and attach to spindle fibre via centromere
Anaphase I: spindle fibres pull, homologous pair of chromosomes separate to opposite sides by independent assortment
Telophase I: chromosomes uncoil, nucleus reforms (left with 2 nuclei)
Meiosis II?
Prophase II: DNA coils to form chromosomes, nucleus breaksdown, spindle fibres form
Metaphase II: chromosomes line up in middle of cell and attach to spindle fibre via centromere
Anaphase II: spindle fibres pull, centromere splits, sister chromatids move to opposite sides by independent assortment
Telophase II: chromatids uncoil, nucleus reforms (left with 4 genetically different nuclei)
Cytokinesis?
separating cell into 4 (each receives a nucleus and organelles/cytoplasm)
How does Meiosis produce Variation?
Crossing Over and Independent segregation
What is crossing over?
occurs in Prophase I of Meiosis I
homologous pairs of chromosomes wrap around each other and swap equivalent sections of chromatids – produces new combination of alleles
What is independent segregation?
-in Anaphase I of Meiosis I – the homologous pairs of chromosomes separate
- in Anaphase II of Meiosis II – the chromatids separate
- independent assortment produces a mix of alleles from paternal and maternal chromosomes in gamete
What happens to DNA mass in meiosis?
quarters
What happens to Chromosome number in meiosis?
halves (haploid)
What is Mutation?
Change in DNA
2 types: Chromosome Mutation and Gene Mutation
What causes chromosome mutation?
In plants, inherit more than one diploid set of chromosomes – called polyploidy
In animals, homologous pair of chromosome do not separate in meiosis, so either inherit one extra or one less chromosome – called non-disjunction
What is a Gene Mutation?
a change in the base sequence of DNA
2 types = substitution and insertion/deletion
substitution = replace one base for another, changes one triplet code can be silent (new triplet code codes for same AA), mis-sense (codes for a different AA, so protein shape changes slightly), non-sense (codes for a stop codon, so polypeptide chain not produced)
insertion = adding a base, deletion = removing a base
both insertion/deletion causes frameshift, all the triplet codes after the mutation changes, so normal polypeptide chain/protein not produced
Semi-conservative replication process?
DNA Helicase breaks hydrogen bonds between the complementary bases
double strand separates, leaves 2 template stands
free complementary nucleotides bind to exposed bases on template strands (A to T, C to G)
DNA Polymerase joins the sugar-phosphate backbone of the new strand
