Neucleotides Flashcards
nucleic acids
polymers made up of monomers
Nucleotides
- phosphate group
- pentose sugar (ribose, deoxyribose)
- organic base (nitrogenous base)
Nucleotide are joined together by phosphodiester bonds in condensation
organic bases
- Double ring structures: Purines (adenine, guanine)
- Single ring structures Pyrimidines (thymine, cytosine, uracil)
Metabolism
All chemical reactions in cells
Catabolism
Use to break chemical bonds, which breakdowns large molecules
Anobalism
Use to build chemical bonds when building larger molecules
ATP as an energy carrier
Adenosine Triphosphate - Molecule that makes energy available formed when chemical reactions release energy
Broken down when energy is needed
Structured of ATP
Three phosphate groups, ribose, adenine
ATP and when energy is needed
When energy is needed in living organisms- ATPase hydrolyses the bond between 2nd and 3rd phosphate groups in ATP leaving 2
ATP hydrolysed
into adenosine diphosphate (ADP) and an inorganic phosphate ion, with release of chemical energy
ATP + water —> ADP + Pi
Reaction is reversible
Phosphorylation
Addition of Phosphate to ADP
ATP transfers
Transfers free energy from energy rich compounds To cellular reactions when needed eg. Glucose
Energy transfer is inefficient and some energies lost as heat
Energy released in respiration, releasing ATP
ATP as a supplier of energy
Hydrolysis
- Hydrolysis of ATP and ADP involves a single reaction, releasing energy immediately. Whereas breakdown of glucose takes longer for energy to be released
ATP as a supplier of energy
One enzyme
Only one enzyme needed to release energy from ATP but many for glucose
ATP as a supplier of energy
smlall amounts
ATP releases energy in small amounts, when needed
Glucose (large, all at once)
ATP as a supplier of energy
coomon source
Provides common source of energy for many different chemical reactions, increasing efficiency and control by the cell
Role of ATP
Provides necessary energy for cellular activity
Role of ATP
Metabolic process
To build large, complex molecules from smaller, simpler molecules
Eg. DNA synthesis from nucleotides
Role of ATP
Active transport
to change shape or carry a proteins in membranes and allow molecules for ions to be moved against the concentration gradient
Role of ATP
Muscle
For muscle contraction, cytokinesis
Role of ATP
Nerve transmission
Sodium - potassium pumps actively transport sodium potassium ions across an axon membrane
Role of ATP
Secretion
the packaging and transport of secretory products into vesicles in cells
structure of DNA
composed of 2 polynucleotides strands wound to form double helix
AGTC
Structure of DNA- bases of sugars
Bases of two sugars face each other, pointing inwards
Adenine lines opposite with thymine, guanine with cytosine
hydrogen bonds join the bases and form complementary pairs
A complementary to T, Joined by 2 hydrogen bonds
G complementary to C, joined by 3 hydrogen bonds
Hydrogen bonds in the structure of DNA
Maintain the shape of the double helix
Two strands in the structure of DNA
Two strands run in opposite directions to each other and are antiparallel
role of DNA
Provide genetic code to synthesise proteins
How is DNA suited for its role
- Very stable molecule, information contents passes from generation to generation without change
- Very large molecule, carries large amounts of genetic information
- Two strands able to separate as they are held by hydrogen bonds
- As base pairs are on the inside of double helix, within the deoxyribose phosphate backbones, the genetic information is protected
structure of RNA
- Single stranded polynucleotide
- Contains pentose sugar ribose
- adenine guanine cytosine uracil
messenger RNA
- Helical, long single stranded molecule
- synthesised in the nucleus and carries a genetic code from DNA to the ribosomes in the cytoplasm
- Different mRNA have different lengths of genes from which they are transcribed
ribosomal RNA
- Found in the cytoplasm and comprises large, complex molecules
- Ribosomes are made of rRNA and protein
- Site of translation of the genetic code into protein
terminal RNA
- Small single stranded molecule, folded into Clover leaf shape
- 3’ End of molecule has base sequence cytosine - cytosine - adenine where specific amino acid the molecule carries is attached
- Molecules of tRNA transport specific amino acids to ribosomes in protein synthesis
Dna replication
Copying of DNA in nucleus during interface
Conservative replication
Where the parental double helix remains intact
Eg. Is conserved and a whole new double helix is made
Semi conservative replication
Parental double helix separates into two strands each of which acts as a template for synthesis of a new strand
Dispersive replication
Two new double helices contained fragments from both strands of the parental double helix
meselson- stahl experiment
cultured bacterium Escherichia coli for several generations with medium containing amino acids made with N15 (heavy)
Bacteria incorporated N15 in nucleotide and eventually DNA contained only N15
Extracted and centrifuged to show low marking.
Bacteria must be washed before next experiments- to be transferred N14 medium to prevent contamination
N14 DNA
Centrifuged- Showed midpoint density
Rules out conservative replication theory as it would produce a bond showing parental molecule that is entirely heavy
Intermediate D N a containing half heavy half light
After 2nd gen
N14 settled at the midpoint and high point
Ruled out dispersive because they would be a mixture of lights and heavy in every strand and only one bond would form
Half of DNA is intermedia and half is light
After 3rd gen
1/4 intermediate
3/4 light
Stages of semi conservative replication
1
DNA Helicase ‘unwinds and unzippes’ DNA molecule
stages of semi Conservative replication
2
This exposes the 2 DNA strands which then act as ‘templates’
stages of semi Conservative replication
3
Free nucleotides collide with their complementary bases and form hydrogen bonds
Stages of semi conservative replication
4
DNA polymerase forms phosphodiester bonds between new adjacent DNA nucleotides
Stages of semi conservative replication
5
Two new DNA molecules are formed each composed of one original template strand and one newly synthesised strand
the genetic code
DNA contains store of genetic information called genes
base sequence directs which amino acids join together
therefore it determines which proteins are made and which reactions can take place in organisms
TRIPLET CODE
biochemical experiments show that
- Polynucleotide strand always has three times the number of bases as amino acids chains is coded for
- If three bases were removed from polynucleotide polypeptide made would have one fewer amino acid
- If polynucleotide had three extra bases, polypeptide would have one more amino acid
coding for amino acids
Three bases code for one amino acid
Therefore four different bases, twenty different amino acids
4^3=64 (More than enough)
Properties of the genetic code
- 3 bases in code each amino acid, therefore is a triplet code
- 64 possible codes but only 20 amino acids found in proteins, more than one triplets can encode each amino acid so code is described as ‘degenerate’/ ‘reduction’
- Code is punctuated: there are 3 triplet codes that don’t code for amino acids. In mRNA ‘stop’ codons and Mark end of a portion to be translated
- Universal: Some triplet codes for the same amino acids
- Non overlapping: each base occurs in only 1 triplet
Intron
Non-coding nucleotide sequence in DNA and pre mRNA- removed from pre mRNA to produce mature mRNA
extron
Coding region in the nucleotide sequence of DNA and pre mRNA that remains present in final mature mRNA, after intron has been removed
In Eukaryotes
Initial RNA version of a code is much longer than the final mRNA and it contains sequences of bases that have to be removed
Pre messenger RNA
RNA is sometimes called pre-mRNA and sequences (introns) are to be removed
introns are cut off
Cut off of the pre MRNA using endonucleases and the sequence left (Extron’s) which are joined together/ spliced with ligases
Protein synthesis: transcription
One strand of DNA acts as a template for the production of mRNA, a complementary section of part of DNA sequence- occurs in the nucleus
Protein synthesis: translation
mRNA acts as a template to which complementary tRNA molecules attach, and the amino acids they carry are linked to former polypeptide - occurs in the ribosomes in the cytoplasm
Transcription Process
first
- DNA helicase ‘unwinds and unzips’ DNA
- Free RNA nucleotide randomly collide with their complementary bases on the coding strand
- RNA polymerase forms phosphodiester bonds between adjacent RNA nucleotides, synthesising mRNA
- It continues to the stop triplet code, then mRNA is released
- mRNA diffuses through the nuclear pores into the cytoplasm, happens in a nucleus
Translation Process
- mRNA associates with a ribosome
- Ribosome covers the first two codons
- A tRNA with a complementary anticodon to the first mRNA codon, H Bonds to it.
- 2nd tRNA with a complementary anticodon to the second mRNA codon
- Peptide bond forms between the 2 amino acids
- First tRNA is released and the ribosome moves along 1 codon.
- This continues until ribosome reaches the stop codon
- Polypeptide chain is released and so is the mRNA
tRNA and amino acid activation
- Once tRNA is released from the ribosome, it is free to collect another amino acid from the amino acid in the cytoplasm
- Energy from ATP is needed to attach the amino acid to the tRNA
- Process of attachment is called amino acid activation
Genes and polypeptides
Experi
- experiments on fungus neurospora crassa showed that radiation damage to DNA prevented a single enzyme from being made
genes and polypeptide
Experiment lead to
- Led to the one - gene - one enzyme hypothesis
- One - gene - one polypeptide hypothesis ( Proteins contain more than one polypeptide eh. Haemoglobin)
- Therefore a gene is a sequence of DNA basis that codes for a polypeptide
Post-transitional modification ( Modification of a polypeptide)
Base sequence of a gene determines the primary structure of a polypeptide
Polypeptides made on ribosomes are transported through the cytoplasm to the golgi body
Primary structure of a polypeptide
Structure is functional, but usually is folded in secondary, tertiary or quantenary structure in the ER
In the Golgi body it may be chemically modified
How polypeptides can be chemically modified
- Carbohydrates: making glycoproteins
- Lipids: making lipoproteins
- Phosphate: making phospho-proteins
