Module 2: Nucleotides and Nucleic Acids Flashcards
Name the 2 types of nucleic acid
DNA (deoxyribonucelic acid)
RNA (ribonucleic acid)
What are the components of a nucleotide?
Nitrogenous base
Pentose sugar
Phosphate group
What are the 5 bases?
Adenine Guanine Thymine Cytosine Uracil
Which of the 5 bases are only in RNA?
Uracil - replaces thymine
Which of the bases purines? Define purine
Adenine and guanine
Larger bases which contain a double carbon ring structure
Which of the bases are pyrimidine? Define pyrimidine
Cytosine, thymine, uracil
Smaller bases which contain a single carbon ring structure
What is complementary bases pairing?
Specific bases pair with specific bases i.e. purine must pair with pyrimidines due to complementary shape.
Which bases are complemenatry to each other?
A with T
C with G
A with U (RNA only)
How does the structure of DNA relate to its function?
1) Info storage = sequence of base pairs stores info to build proteins.
2) Long molecule = means that lots of info can be stored.
3) Base pairing rule = complementary strands can be replicated giving exact copies.
4) double helix, anti-parallel strand = very stable, essential for important molecules.
5) H bonds = easily unzipped for semi-conservative replication.
Where is almost all DNA found in eukaryotic cells?
Nucleus
How are nucleotides joined together?
Condensation reactions between the deoxyribose sugar and the phophate of another nucleotide.
From 5’ to 3’
Name of covalent bond that forms in a condensation reaction between nucelotides?
Phosphodiester bond
Forms sugar-phosphate backbone
Define the term anti-parallel
2 strands of DNA run in the opposite direction to one another
How are strands held together between bases?
Hydrogen bonds
How many H bonds between complementary bases?
2 H bonds between A and T
3 H bonds between C and G
What is the benefit of having H bonds between bases?
Allow the DNA molecule to easily unzip for DNA replication. Makes the molecule very stable and protects the base sequences
Differences between DNA and RNA
RNA is a single strand - DNA a double strand
RNA contains uracil instead of thymine
RNA has a ribose sugar instead of deoxyribose
What are the 3 types of RNA?
mRNA, rRNA, tRNA
Describe mRNA
Long single strand formed into a helix
Made in the nucleus
Passes into cytoplasm via nuclear pores
Moves to ribsomes for translation
Describe rRNA
Made in nucleolus
Found in cytoplasm
Forms in ribosomes
Ribosomes formed of rRNA and proteins
Describe tRNA
Forms clover-leaf shape
One end attaches to a specific amino acid
Other end has a triplet of bases used in protein synthesis known as an anticodon
Describe the process of DNA extraction
Grind smaple in a mortar and pestle to break down the cell wall
Mix sample with detergent to break down the plasma membrane, releasing cell contents into solution
Add salt to break the H bonds between DNA and water molecules
Add protease enzyme to break down the proteins assciated with the DNA in the nuclei
Add a layer of cold ethanol causing the DNA to precipitate out of solution
Why shoule the temperature be kept low throughout the extraction of DNA?
Reduce the activity of enzymes, which would break down the DNA and prevent extraction
Why does the detergent break down the plasma membrane?
Disrupts the membrane structure making it more permeable and fluid, causing the phospholipids to form a suspension in the aqueous solution
Why do cells require energy?
1) Synthesis = large molecules like proteins
2) Transport = molecules or ions across plasma membrane by active transport
3) Movement = protein fibres in muscle cells for contraction
How is energy supplied to cells?
Adenosine triphosphate (ATP) supplies energy
Components of ATP
Ribose sugar
Adenine base
3 phosphate groups
What is ATP also known as for all living things?
Universal energy currency
What type of reaction is the removal of a phosphate group in ATP?
Hydrolysis
What are hydrolysis reactions of ATP said to be?
Couple. Happen simultaneously in association with an energy requiring reaction
What is the negative of ATP?
The insatbility of the phosphate bond means its not a good long-term energy store.
How is ATP formed?
The breakdown of fats and carbohydrates by cellular respiration. A phosphate group is reattached to the ADP molecule to reform ATP
What is the process of forming ATP from ADP known as? What type of reaction is it?
Phosphorylation
Condensation reaction
What type of energy store is ATP good for?
Immediate energy store as it is not needed as a large store
How do the properties of ATP relate to its function?
1) Small = moves easily in and out of cells
2) Soluble = energy requiring processes happenin aqueous environments
3) Bonds between phosphates = large enough to provide immediate energy for cellular reactions, but not so large to waste energy as heat
4) Release energy is small quantities = energy not wasted as heat
5) Easily regenerated = recharged with energy
When does DNA replication occur?
During interphase
Describe the process of DNA replication
1) 2 strands of DNA must unwind (using gyrase) and split apart
2) H bonds are broken using DNA helicase, exposing bases
3) Free nucleotides line up against DNA strands. Nucelotides activated by extra phosphate groups using complementary base pairing
4) This occurs in the 5’ to 3’ direction (leading strand) using DNA polymerase
5) The lagging strand (3’ to 5’) uses primers and Okazaki fragments with DNA polymerase
6) DNA polymerase joins the 2 strands together forming 2 new DNA molecules
7) Ligase adds H bonds between bases
Define semi-conservative replication
Molecules have one original strand and one new strand
Define gene
A length of DNA which codes for one polypeptide or a length or RNA that helps regulate gene expression
Define locus
Location of a gene on a chromosome
Define allele
An alternative form of gene
Define triplets
3 DNA bases code for 1 amino acid
Define degenerate code
Most amino acids have more than one codon that can code for them. This can reduce the impact of point mutation
Define universal
The tripet code TCG codes for the amino aicd serine in almost all organisms. There are some variations, a strong case for common ancestry.
All organims use thr same code, but sequences of bases coding for each individual protein will be different
Define non-overlapping
Read starting from a fixed point in groups of 3 bases (codon)
How does DNA control all metabolic activities in cells?
Chemical reactions control the cells activities
All chemical/metabolic reactions are catalysed bby enzymes
Enzymes are proteins
Sequence of bases of DNA codes for polypetide and protein molecules.
Hence DNA controls metabolic activities
What are the 2 stages of ptrotein synthesis?
Transcription and translation
Initiation in transcription
RNA polymerase binds to DNA at promoter region
Unwinding of DNA due to helicase
H bonds broken between bases and bases exposed
Elongation in transcription
Free RNA nucleotides pair up with exposed complementary bases on template (anti-sense) strand in 5’ to 3’ direction
Added using RNA polymerase
Coding strand (sense strand) not transcribed
Termination in transcription
Stops at the end of a gene
Stop codon produced on mRNA
H bonds catalysed by RNA polymerase, before detaching
Phosphodiester bonds form in a condensation reaction.
mRNA levaes the nucleus via the buclear pores into the cytoplasm
Describe translation
mRNA binds to a ribsome in the cytoplasm or RER
Ribosome reads sequences of bases in the 5’ to 3’ direction until start codon of AUG
tRNA carrying amino acid methionine is complementary to codon on mRNA and will bind
Temp H bonds form
Each tRNA molecule carries a specific amino acid. One codon is read at a time
Peptide forms between amino acids (condensation) with peptidyl transferase catalysing
Stop codon found and polypeptide chain released and translation ends
