2.1.3 - NUCLEOTIDES + NUCLEIC ACIDS Flashcards
What are the molecules in a nucleotide?
- Carbon
- Hydrogen
- Oxygen
- Nitrogen
- Phosphorus
What is a nucleotide?
The monomer that makes up DNA and RNA (types of nucleic acid)
What are the three main components of DNA nucleotides?
- A deoxyribose sugar with hydrogen at the 2’ position (carbon)
- A phosphate group
- One of four nitrogenous bases - adenine (A), cytosine(C), guanine(G) or thymine(T)
What are the three main components of RNA nucleotides?
- A ribose sugar with a hydroxyl (OH) group at the 2’ position (carbon)
- A phosphate group
- One of four nitrogenous bases - adenine (A), cytosine(C), guanine(G) or uracil (U)
How do nucleotides join together?
Phosphodiester bonds
What type of base are adenine and guanine?
Purine
What type of base are cytosine and thymine?
Pyrimidine
Describe the structure of a purine base.
Contains two carbon-nitrogen rings joined together
Describe the structure of a pyrimidine base.
Only has one carbon-nitrogen ring
(smaller than a purine base)
Describe the structure of DNA.
- 2 antiparallel strands
- Very long
- Deoxyribose pentose sugar
- Adenine, cytosine, guanine, thymine
Describe the structure of RNA.
- 1 strand
- Relatively short
- Ribose
- Adenine, cytosine, guanine, uracil
State the components of ATP.
Adenosine Triphosphate contains adenine, a ribose sugar and three phosphate groups
State the components of ADP.
Adenosine Diphosphate contains adenine, a ribose sugar and two phosphate groups
Define phosphorylate
introduce a phosphate group into (a molecule or compound)
What does ATP do?
- Provides energy for chemical reactions in the cell
- Synthesised from ADP and inorganic phosphate using the energy from an energy-releasing reaction (e.g. breakdown of glucose in respiration
- ADP is phosphorylated to form ATP and a phosphate bond is formed
- Energy is formed in the phosphate bond
- When energy is needed by a cell, ATP is broken back down into ADP and inorganic phosphate - energy is released from the phosphate bond and used by the cell
How are polynucleotides formed?
- Nucleotides join up between the phosphate group of one nucleotide and the sugar of another via a condensation reaction - forms a phosphodiester bond (consisting of the phosphate group + 2 ester bonds
- The chain of sugars and phosphates is known as the sugar-phosphate backbone
- Polynucleotides can be broken down into nucleotides again by breaking the phosphodiester bonds (hydrolysis reaction)
How is a double helix formed?
- Two DNA polynucleotides strands join together by hydrogen bonding between the bases
- Each base can only join with one particular partner (complementary base pairing)
- Adenine always pairs with Thymine (A-T) and Cytosine always pairs with Guanine (C-G) - A prune always pairs with a pyrimidine
- 2 H bonds form between A and T, and 3 H bonds form between C and G
- Two antiparallel (running in opposite directions) polynucleotide strands twist to form the DNA double helix
How does DNA copy itself before cell division?
- DNA helicase (enzyme) breaks hydrogen bonds between the two polynucleotide DNA strands - the helix unzips to form two single strands
- Each original single strand acts as a template for a new strand - free-floating DNA nucleotides join to the exposed bases on each original template strand by complementary base paring (A with T and C with G)
- The nucleotides of the new strand are joined together by the enzyme DNA polymerase - forms the sugar-phosphate backbone | H bonds form between the bases on the original and new strand - strands twist to form a double helix
- Each new DNA molecule contains one strand from the original DNA molecule and one new strand
What may randomly occur during DNA replication?
- A random, spontaneous mutation may occur
- A mutation is any change to the DNA base sequence
- Don’t always have an effect, but can also the sequence of amino acids in a protein
^— may cause abnormal protein to be produced which may function better or not work at all
What is a gene?
A sequence of DNA nucleotides that codes for a polypeptide
Amino acid sequence in a polypeptide forms the primary structure
How are amino acids coded in DNA?
- Each amino acid is coded for by a sequence of three bases (called a triplet) in a gene
- Difference base sequences code for different amino acids - so the sequence of bases in a section of DNA is a template that is used to make proteins during protein synthesis
What happens to DNA in protein synthesis?
- DNA molecules are found in the nucleus of the cells, but the organelles that make proteins are found in the cytoplasm
- DNA is too large to move out of the nucleus, so a section is copied into mRNA - this is transcription
- mRNA leaves the nucleus and joins with a ribosome in the cytoplasm, where it can be used to synthesise a protein - this is translation
What are the three types of RNA
- Messenger RNA (mRNA)
- Transfer RNA (tRNA)
- Ribosomal RNA (rRNA)
What is the function of mRNA?
- made in the nucleus
- three adjacent bases are called a codon
- carried the genetic code from the DNA in the nucleus to the cytoplasm, where its used to make a proteins during translation
What is the function of tRNA?
- found in the cytoplasm
- has an amino acid binding site at one end + a sequence of three bases at the other end called an anticodon
- carried the amino acids that are used to make proteins to the ribosome during translation
What is the function of rRNA?
- forms the two subunits in a ribosome
- the ribosome moves alone the mRNA strand during protein synthesis - the mRNA in the ribosome helps to catalyse the formation of peptide bonds between the amino acids
What is the genetic code?
The sequence of base triplets (codons) in DNA or mRNA, which codes for specific amino acids
Why is the genetic code described as non-overlapping?
In the genetic code, each base triplet is read in sequence, separate from the triplet before it and after it
Base triplets don’t share their bases
Why is the genetic code describe as degenerate?
- There are more possible combinations of triplets than there are amino acids (20 amino acids but 64 possible triplets)
- Means that some amino acids are coded for by more than one base triplet (e.g. tyrosine can be coded for by UAU or UAC)
Why is the genetic code describe as universal?
The same specific base triplets code for the same amino acids in all living things (e.g. UAU codes for tyrosine in all organisms)
What are the two stages of protein synthesis called?
Transcription and Translation
Describe what happens in transcription
- RNA polymerase binds to DNA + breaks H bonds
- Free RNA nucleotides align with DNA template through comp. base pairing
- RNA polymerase catalyses formation of phosphodiester bonds between adjacent RNA nucleotides
^– Complementary mRNA is formed, carrying same base sequence as the DNA sense strand - Process ends when RNA polymerase reaches a stop codon, detaches from DNA + terminates transcription
- mRNA is release, detaches from DNA = DNA rewinds into double helix
Describe what happens in translation
- Ribosome attaches to mRNA strand at start codon
- tRNA molecule carrying a specific amino acid + with an anticodon complementary to start codon binds to mRNA
- Second tRNA molecule with anticodon complementary to next mRNA codon + carrying specific amino acid attaches to mRNA
- Amino acids carried by the first 2 tRNA molecules linked together via peptide bond using ATP
- First tRNA molecule detaches from mRNA + is free to collect another amino acid for future use
- Ribosome moves along mRNA, allowing another tRNA molecule (carrying next amino acid) to bind to next codon on mRNA
- this repeats, w/ 2 tRNA molecule attached to mRNA at any point
^– until stop codon on mRNA is reached
What are the three main components of nucleotides?
- A pentose sugar (5 carbon atoms)
- A nitrogenous base
- A phosphate group
State the function of DNA
Stores genetic information
State the function of RNA
- Transfers genetic information
- Forms ribosomes with proteins
What is DNA replication semi-conservative?
SEMI-CONSERVATIVE REPLICATION because half of the strand in each new DNA molecule are from the original DNA piece
DNA replication is really accurate
Describe the structure of ATP
- Adenine
- Ribose sugar
- 3 phosphate groups
