Nucleic Acids Flashcards
How are nucleotide bases split up
Pyrimidines: Thymine, uracil, cytosine
Purines: guanine, adenine
Compare structure of DNA nucleotide to RNA nucleotide
DNA:
- deoxyribose
- thymine
- double-stranded
RNA:
- ribose
- uracil
- single stranded
What are the functions of DNA
- Stores and transmits genetic information.
- Instructions for development, functioning, growth, and reproduction.
- Essential for creating proteins that regulate cellular processes.
- Regulates replication and repair of cells.
- Crucial role in inheritance, passing genetic information to future generations.
- Relies on RNA intermediaries (mRNA, tRNA, rRNA) for protein synthesis in the cytoplasm.
What is mRNA
RNA that transfers genetic information from DNA to ribosomes
what is transcription
Converts genetic information from DNA to mRNA.
describe the structure of mRNA (4)
- Messenger RNA (mRNA): Single-stranded molecule transcribed from DNA.
- Codons: Sequences of three nucleotides on mRNA.
- Encode specific amino acids during protein synthesis.
- Start codon AUG initiates translation (methionine).
- Stop codons (UAA, UAG, UGA) terminate translation.
- mRNA Length: Shorter than DNA due to lack of introns.
- Splicing removes non-coding introns, leaving only exons.
- Methylated Cap: Modification of first nucleotide with methyl group.
- Improves mRNA binding to ribosomes and nuclear export.
- Poly(A) Tail: Stretch of adenine nucleotides added to 3’ end post-transcriptionally.
- Protects mRNA from degradation by enzymes.
what is rRNA
RNA that makes up ribosomes along with protein (rRNA).
what is the role of rRNA in translation (2)
- Synthesises proteins by decoding mRNA.
- rRNA provides structural stability and positions mRNA and tRNA molecules for efficient protein synthesis.
- Also provides enzymes for the formation of the peptide bond: Peptidyl transferase
describe the structure on ribosomes
- consists of both ribosomal RNA (rRNA) and protein components.
- The rRNA and proteins bind tightly to form two types of 3D structure: a large subunit and a small subunit.
whats the role of tRNA
- Crucial in delivering amino acids to ribosome during translation.
- Ensures correct amino acid incorporation into growing polypeptide chain.
Describe teh structure of tRNA
- tRNA is a small molecule (~80 nucleotides).
- Single stranded and folded into a clover leaf shape with one end of the chain slightly longer.
- This longer section is attached to an amino acid.
- Each tRNA can carry a different amino acid.
- 3 bases at the opposite end of the tRNA are called an anticodon.
- Each amino acid has a different anticodon.
- The anticodon pairs with the complementary codon on the mRNA.
whats the function of tRNA
- Two tRNA molecules, each with distinct anticodon (UAC, AGG).
- Complementary tRNA fits into P site first, then A site.
- Peptidyl transferase enzyme catalyzes peptide bond formation between amino acids.
whats the function of eukaryotic chromosomes
- Chromosomes contain genes which code for proteins and polypeptides and so control all cellular functions
- made up of “packaged” DNA (DNA can replicate) thereby allowing genetic information to be passed from one generation to another
describe ethe structure of chromosomes (in dividing and non dividing cells)
- Chromosomes are made of chromatin: DNA and proteins
- Chromosomes located in the cell nucleus
- Each duplicated chromosome exists as 2 sister chromatids (after S phase)
- The chromatids are most closely attached at the centromere
P-arm = short arm
Q-arm = long arm
How do chromosomes appear in diving/non dividing cells
- Non-dividing cell –They partially unravel and chromatin appears as a diffuse mass
- Dividing cell –They condense and can be seen as chromosomes
what are telomeres, what is their structure and function.
Telomeres are protective regions at the end of each chromosome
- Do not contain genes
- Contain short sections of DNA repeated hundreds or even thousands of times
- act like the plastic caps of shoelaces- prevent chromosome from deterioration at the ends.
describe the process of condensation in chromosomes
Naked DNA - Nucleosome- chromosome -Solenoid formation- 30nm chromatin fibre
- Naked DNA - not associated with histone proteins or other molecules and are in their free, unbound form (double helix, sugar phosphate backbone, antiparallel)
- Nucleosome- basic structural units of chromatin, consisting of DNA wrapped around histone protein
- Chromatosome is a number of loosely associated nucleosomes
- Solenoid Formation : Multiple nucleosomes come together to form a solenoid shape (a spiral shape)
- 30-nm chromatin fibre- The chromatin fibre undergo further compaction through the coiling of nucleosomes into a 30-nanometer fibre.
How is gene expression regulated
- The more condensed DNA is the more transcription may be restricted as access to the active gene in DNA is reduced
- heterochromatin (tightly condensed)
- euchromatin (loosely condensed)
Describe heterochromatin, how does it affect gene expression
- tightly condensed
- maintains the structural integrity of chromosomes, suppresses the expression of repetitive DNA elements
Describe euchromatin, how does it affect gene expression
- loosely condensed
- Essential for gene expression, transcriptional regulation, and cellular function. It contains most actively transcribed genes and regulatory elements required for cellular processes like growth.
How are histone tails modified
- tails have a positive charge so can associate with negative DNA
- Adding an acetyl group to the tail (acetylation) neutralises the charge, making DNA less tightly coiled and increasing transcription
- Adding a methyl group to the tail (methylation) maintains the positive charge, making DNA more coiled and reducing transcription
What are the steps to semi-conservative replication (6)
- DNA helicase breaks hydrogen bonds between base pairs.
- This destabilises DNA, causing the two strands to separate into a replication fork.
- Helicase progresses along DNA, continuing to unwind the double helix, like a zipper
- SSB proteins bind to single-stranded DNA to prevent it from looping onto itself
-
Leading strand formed by :
- DNA polymerase III adds nucleotides ONLY in the 5’ to 3’ direction.
- Synthesizes leading strand continuously in 5’ to 3’ direction.
- Continuous replication occurs on leading strand. -
Lagging Strand formed by:
- synthesized discontinuously in the 5’ to 3’ direction, which is opposite to the direction of the replication fork movement
- As the replication fork opens, DNA polymerase III synthesizes short fragments of DNA (Okazaki Fragments)
- DNA ligase then joins the adjacent Okazaki fragments together, forming a continuous strand of DNA.
why are RNA primers added to DNA during DNA replication
- Because DNA polymerase III requires a free OH group to add the incoming nucleotides
- serve as starting points for DNA synthesis by providing a free 3’ OH group for DNA polymerase III to extend from
what is teh role of RNA primase in DNA replication
- primase enzyme synthesizes short RNA primer sequences complementary to the DNA template at the replication fork
whats the purpose of polymerase III in DNA replication
- used in replication of both leading strands and the okazaki frgamets in the laggings strand
- DNA polymerase synthesizes DNA in the 5’ to 3’ direction because it requires a free hydroxyl (OH) group on the 3’ end of the sugar molecule to attach to the phosphate group of the incoming nucleotide.
Role of DNA polymerase I in DNA replication
- role is to remove RNA primers and replace them with DNA nucleotides after DNA polymerase III has synthesized the new DNA strands
- occurs in lagging strands
what is the non overlapping code
each base is only used once in one triplet
what is the degenerate code
more than one triplet can code for the same amino acid
what is the universal code
can be applied to the DNA of all living organisms from bacteria, to plants to animals
what are the stop and start signals
- start (AUG) codon
- 3 stop codons (UAA, UGA and UAG)
which was is the mrna codon read
always read 3→5 so mrna can be synthesised in 5→3 direction
define translation
The formation of a protein, at ribosomes by assembling amino acids into a particular sequence according to the coded instructions carried from the DNA to the ribosomes by the mRNA.
deifine introns
A non-coding region of DNA: Sequence of nucleotides within a gene that does not remain in the mRNA transcribed from that gene (in Eukaryotes)
define exons
lengths of DNA which code for proteins (in Eukaryotes)
describe the process of transcription (6)
- RNA polymerase II binds to promoter region of the gene and unwinds the DNA to expose the bases
- Free ribonucleotides base pair with the exposed bases of the unwound template strand.
- RNA polymerase links nucleotides to the 3’ end of the with the growing mRNA strand via phosphodiester bonds.
- Once RNA polymerase reaches the transcription termination site, it detaches from the DNA template
- mRNA is released, DNA winds back in a dsDNA form.
- mRNA is transported to the cytoplasm via a nuclear pore.
- introns are spliced out
describe the process of translation (12)
- mRNA attaches to the small subunit
- Initiation tRNA carrying Methionine loaded into the P site of small subunit
- Anticodon in tRNA aligns with start codon AUG on mRNA
- Large subunit binds to complete the ribosome
- Complementary tRNA enters the A site, bringing its amino acid with it.
- Anticodon in the A site tRNA aligns with codon on mRNA
- The two amino acids are aligned
- A peptide bond is formed, catalysed by peptidyl transferase
- Ribosome moves along the mRNA.
- The earlier tRNA enters E site to exit the ribosome.
- Remaining tRNA moves to P site, exposing A site codon for a new tRNA
- The process continues, until the ribosome reaches a stop codon
- At the stop codon in A site, translation termination factors (release factors) signal the ribosome to split into subunits.
- It dissociates from the mRNA.
- Newly synthesised protein is released.
what are the different types of DNA mutations
”- Lethal mutation – causes organism to die prematurely
- Conditional mutation – produces phenotypic effect only under certain conditions (e.g. temperature sensitive)
- Loss-of-function mutation – reduces or abolishes (null mutation) activity of gene
- Gain-of-function – increases activity of gene”
what are mutagens and examples
”- Certain environmental factors, known as mutagens, can increase the rate at which mutations occur:
- Ionising radiation
- Viruses and microorganisms
- Chemicals”
define gene mutations (egs)
”- changes or alterations in the DNA sequence-
- Base substitution (point mutation)
- Base insertion or deletion - Frameshift”
what does silent, missense and nonsense mean
“silent- no change
missense - changes the amino acid
nonsense- creates a stop codon”
describe chromosome disorders and examples
”- changes in the number or structure of the chromosome
- e.g. Down’s Syndrome (Trisomy 21)
- Inversion, duplication, deletion, translocation, non-disjunction”
what’s the difference between gametic and somatic mutations
“Gametic mutations
- Take place in the reproductive organs within cells producing gametes
- They are inherited by subsequent generations
Somatic mutations
- “Acquired” mutations
- Occur in a body cell after fertilisation
- They are not inherited”
define metabolism (+ 2 types)
- Metabolism is all the chemical reactions that take place within the body
-Anabolic reactions
-Catabolic reactions
What are 2 types of metabolic storage disorders
Aquired disorders and genetic disorders
What are aquired metabolic storage disorders
- caused by the ingestion of plants/toxins that contain inhibitors of specific catabolic enzymes.
For example, locoweed toxicity
What are genetic metabolic storage disorders
- Usually autosomal recessive
- Animals are typically normal at birth; clinical signs often occur within the first weeks to months of life.
- These diseases are progressive and are usually fatal - specific treatments do not exist
what are lysosomal metabolic storage disorders
Build up of waste products causes cell damage
Generally the earlier the onset of clinical signs the more rapidly the disease will progress
- Lysosomal storage diseases are a group of inherited diseases (usually recessive) resulting in abnormal lysosome function
- Lack of enzyme involved in metabolism of a substance – substance builds up and is stored in lysosomes
- Lysosomal engorgement and therefore the cell’s metabolic function is compromised
what is alpha-mannosidosis and how does it work
- it is a lysosomal storage disorder
- Lack of the enzyme alpha-mannosidase involved in breaking down mannose-containing compounds, which is essential in the modification of proteins
- build up of mannose rich compounds in lysosomes
what causes alpha mannosidosis
- In affected individuals a base substitution causes an amino acid substitution
- Results in non-functional enzyme
Which breeds are affected by alpha mannosidosis and what are the clinical signs
- Clinical signs include ataxia, head tremor, aggression, paralysis and death
- Breeds affected include Aberdeen Angus and Galloway cattle
what is gylycogenosis and what is it caused by and what breeds afre affected
- metabolic disorder caused by a deficiency of an enzyme or transport protein affecting glycogen synthesis, glycogen breakdown, or glucose breakdown, typically in muscles and/or liver cells.
- Can be caused by phosphofructokinase deficiency and has been identified in English Springer Spaniels and American Cocker Spaniels
what is phosphofructokinase and how can a mutation in it cause an affect
- PFK involved in the first stage of respiration
- UGG mutated to UAG (stop) so it shortens the polypeptide
- Exercise intolerance, Muscle cramps - respiration cant occur
