Nucleotides And Nucleic Acids :). Flashcards
What’s a nucleotide made up of?
A pentose sugar (sugar with 5 carbon atoms)
A nitrogenous (nitrogen-containing) base
Phosphate group
What elements do all nucleotides contain?
CHONP
Why are nucleotides really important?
They’re monomers that make up DNA and RNA both types of nucleic acid
DNA is used for
To store genetic information
The instructions an organism needs to grow and develop
RNA used for?
To make proteins from instructions in DNA
What are ADP and ATP?
Special types of nucleotide
Used to store and transport energy in cells
What is the pentose sugar in a DNA nucleotide
Deoxyribose
DNA
Deoxyribonucleic acid
What does each DNA nucleotide contain the same?
The same sugar and a phosphate group
The base on them varies
What are the four DNA bases?
Adenine and thymine
Cytosine and guanine
What type of base are adenine and guanine?
A type of base called purine
What type of base are cytosine end thymine?
Phyrimidine
A purine base contains
Two carbon-nitrogen rings joined together
Pyrimidine base
Only had one carbon-nitrogen ring
Pyrimidine base is smaller than a purine base
What does a molecule of DNA contain?
Two polynucleotide chain
Each chain is made up of lots of nucleotides joined together
RNA
Ribonucleic acid
What does a RNA contain?
A nucleotide with a ribose sugar
How are RNA and DNA nucleotides similar?
Have phosphate group
One of four different bases
Difference between RNA and DNA
RNA uracil (pyrimidine) DNA thymine (pyrimidine)
What does a molecule of RNA contain?
Made up of single polynucleotide chain
What type of nucleotide are ADP and ATP?
Phosphorylated nucleotides
What do to phophorylate a nucleotide?
Add one or more phosphate groups in it
ADP
Adenosine diphosphate
ATP
Adenosine triphosphate
ADP contains
Base adenine
Sugar ribose
Two phosphate groups
ATP contains
Base adenine
Sugar ribose
Three phosphate groups
ATP provides what
Energy for chemical reactions in the cell
ATP synthesised from what?
ADP and inorganic phosphate using energy from an energy-releasing reaction
E.g. Breakdown of glucose in respiration
ADP is phosphorylated to form ATP and phosphate bond is Forbes
How is energy stored in phosphorylated nucleotides?
Stored in phosphate bond
When energy needed by a cell
ATP is broken down into ADP and inorganic phosphate
Energy is released from phosphate bonds and used by the cell
What is a nucleotide
A type of biological molecule
Where do nucleotides join up?
Between phosphate group of one nucleotide and the sugar of another
What do nucleotides form?
A phosphodiester bond (consisting of the phosphate group and two ester bonds)
What are the sugars and phosphates known as?
Sugar- phosphate backbone
What can polynucleotides be broken down into?
Nucleotides again breaking the phosphodiester bonds
How do 2 DNA polynucleotides join together?
By hydrogen bonding between bases
What can each base join?
Complementary base pairing
Join with one particular partner
Complementary base pairing
Base pairs?
Adenine and thymine
Cytosine and guanine
What are the purine bases?
Adenine and guanine
What are the pyrimidine bases?
Thymine and cytosine
A purine base always pairs with a?
Pyrimidine
How can bonds between adenine and thymine?
Two hydrogen bonds
How many bonds between cytosine and guanine?
Three hydrogen bonds
What does Antiparallel mean?
Running in opposite directions
What do two Antiparallel polynucleotide strand do?
Twist to form the DNA double-helix
What can you use to investigate structure of DNA and other nucleic acids?
Computer modelling
How can you purify DNA?
Using a precipitation reaction
Putrifying DNA using precipitation reaction step 1?
Break up cells in your sample. You can use a blender to do this
Putrifying DNA using precipitation reaction step 2?
Make up a solution of detergent (dilute washing-up liquid will do), salt (sodium chloride and distilled water)
Putrifying DNA using precipitation reaction step 3?
Add broken-up cells to a beaker containing detergent solution. Incubate beaker in water bath at 60 degrees for 15 minutes
Putrifying DNA using precipitation reaction step 4?
Once incubated, put beaker in an ice bath to cool the mixture down. When cooled, filter the mixture. Transfer a sample of your mixture to a clean boiling tube
Putrifying DNA using precipitation reaction step 5?
Add protease enzyme to the filtered mixture. These will break down some proteins in the mixture, e.g. Proteins bound to DNA. Adding RNase enzyme will break down any RNA in the mixture
Putrifying DNA using precipitation reaction step 6?
Slowly dribble some cold ethanol down the side of the tube so it forms a layer on top of the DNA-detergent mixture
Putrifying DNA using precipitation reaction step 7?
If you leave the tube for a few minutes the DNA will form a white precipitate (solid) which can remove from tube using a glass rod
Why did the solution in step 3 involve detergent, salt and a water bath?
The detergent in the mixture breaks down the cell membrane. The salt bonds to the DNA and causes it to clump together. The temperature of the water bath should stop enzymes in the cells from working properly and breaking down the DNA
When does DNA copy itself?
Before cell division so that each new cell has the full amount of DNA.
How does DNA copy itself step 1?
DNA helicase (enzyme) breaks down the hydrogen bonds between two polynucleotide DNA strands. The helix unzips to form two single strands.
How does DNA copy itself step 2?
Each original 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 pairing
How does DNA copy itself step 3?
Nucleotides of new strand are joined together by enzyme DNA polymerase forming sugar-phosphate backbone. Hydrogen bonds form between the bases on the original and new strand. The strands twist to form a double-helix
How does DNA copy itself step 4?
Each new DNA molecule contains one strand from the original DNA molecule and one new strand
What is the sort of copying involved in DNA copying itself called?
Semi-conservative replication because half of its strands in each new DNA molecule are from the original piece of DNA (i.e. The new molecule contains one old strand and one new strand)
What is DNA replication?
Accurate it has to be to make sure genetic information is conserved (stays the same) each time the DNA in a cell is replicated
What happens every so often in DNA replication?
A random, spontaneous mutation occurs
What’s a mutation
Any change to the DNA sequence.
Explain effects of mutations
Don’t always have an effect
Can alter sequence of amino acids in a protein causing an abnormal protein to be produced. The abnormal protein may function better than normal protein or it may not work at all
What is a gene?
A sequence of DNA nucleotides that codes for a polypeptide
What does the sequence of amino acids in a polypeptide do?
Form the primary structure of a protein
Different proteins have?
Different number and order of amino acids
What’s does the order of the nucleotides based in a gene determine?
The order of amino acids in a particular protein
What is each amino acid coded for by?
A sequence of three bases (triplet) in a gene
Different sequences of bases code for what?
Different amino acids. So the sequence of bases in a section of DNA is a template that’s used to make proteins during protein synthesis
Why can’t protein synthesis happen in the nucleus?
DNA molecules are in the nucleus but other organelles that make protein are found in the cytoplasm
Why can’t DNA leave the nucleus and how is the information going to the cytoplasm as a result?
It is too big so a section is copied into messenger RNA (transcription). Messenger RNA leaves nucleus and joins with ribosome in cytoplasm where it can be used to synthesise a protein (translation)
RNA remember is
Single polynucleotide strand containing uracil as a base instead of thymine. Uracil is always paired with adenine during protein synthesis
Three types of RNA
Messenger RNA (mRNA) Transfer DNA (tRNA) Ribosomal RNA (rRNA)
Describe messenger RNA
Made in nucleus
Three adjacent bases are a codon
Carries genetic code from DNA in nucleus to cytoplasm where it’s used to make a protein during translation
Transfer RNA?
Found in cytoplasm
Has amino acid binding site at one end and a sequence of 3 bases at the other and a sequence of three bases at the other end is called an anticodon
Carries amino acids that are used to make proteins to ribosomes during translation
Ribosomal RNA?
Forms two subunits in a ribosome (along with proteins)
Ribosomes move along mRNA strand during protein synthesis. rRNA in ribosomes helps to catalyse formation of peptide bonds between the amino acids
Three adjectives for genetic code?
Non-overlapping
Degenerate
Universal
What is genetic code?
Sequence of base triplets (codons) in DNA or mRNA which codes for specific amino acids
How is each base triplet read in genetic code?
In sequence separate from triplet before it and after it. Base triplets don’t share their bases so code is non-overlapping
Why is genetic code degenerate?
More possible combinations of triplets than there are amino acids (20 amino acids but 64 possible possible triplets). This means that some amino acids are coded for by more than one base triplet e.g. Tyrosine can be coded for UAU or UAC
How does the cell know when to start or stop production of protein?
Some triplets are used to tell the cell when to start and when to stop production of a protein-these are called start and stop signal (start or stop codons) found at the beginning and the end of a gene e.g. UAG is a stop signal
What are codons and anticodons sometimes referred to as?
Triplets
How is genetic code universal?
Same specific base triplets code for the same amino acids in all living things e.g. UAU codes for tyrosine in all organisms
What is the first stage of protein synthesis?
Transcription
When does transcription start?
When the RNA polymerase (an enzyme) attaches to DNA double-helix at the beginning of a gene
What’s stage 2 of transcription?
Hydrogen bonds between the two DNA strands in the gene break, separating the strands and the DNA molecule uncoils at that point
Stage 3 of transcription
One of the strands is then used as a template to make mRNA copy
Stage 4 transcription
The RNA polymerase lines up free RNA nucleotides alongside the template strand. Complementary base pairing means that the mRNA strand ends up being a complementary copy of the DNA template strand (except base T is replaced with U in RNA)
Step 5 transcription
Once the RNA nucleotides have paired up with their specific bases on the DNA strand they’re joined together forming an mRNA molecule
Transcription stage 6
The RNA polymerase moves along the DNA separating the strands and assembling the mRNA strand
Transcription stage 7
The hydrogen bonds between the RNA polymerase has passed by and the strands coil back into a double-helix
Where does translation happen?
At the ribosomes in the cytoplasm
What’s the goal of translation?
Amino acids are joined together to make a polypeptide chain (protein) following the sequence of codons carried by the mRNA
Stage 1 translation
mRNA attached itself to a ribosome and transfer RNA molecules carry amino acids to the ribosomes
Stage 2 translation?
A tRNA molecule with anticodon that’s complementary to the start codon of mRNA attached itself to the mRNA by complementary base pairing
Stage 3 translation?
A second tRNA molecule attracted to itself to the next codon on the mRNA in the same way
Step 4 translation
Ribosomal RNA in the ribosome catalyses the formation of a peptide bond between two amino acids attached to the transfer RNA molecules. This joins the amino acids together. The first tRNA molecules moves away, leaving its amino acid behind
Step 5 translation?
A third tRNA molecule binds to the next codon on the mRNA. Its amino acid binds to the first two and second tRNA molecule moves away
Translation stage 6?
This process continues producing a chain of linked amino acids (a polypeptide chain) until there’s a stop codon on the mRNA molecule
Last stage of translation?
The polypeptide chain moves away from the ribosomes and translation is complete
What is protein synthesis also called?
Polypeptide synthesis as it makes a polypeptide
