1.5: DNA and Protein Synthesis Flashcards
What is nucleic acid?
A polymer of nucleotide molecules
What is the definition of DNA?
a polymer of nucleotide molecules that form the instructions for the synthesis of proteins found within organisms. These nucleotides contain the 5-carbon sugar deoxyribose.
What does DNA stand for?
Deoxyribonucleic acid
What does RNA stand for?
Ribonucleic acid
What is the definition of RNA
a single stranded polynucleotide molecule that exists in 3 forms. Each plays the part in the synthesis of proteins
What is a nucleotide?
The monomer of nucleic acids consisting of a phosphate, a sugar and a nitrogenous base.
What is ribose?
The 5-carbon (pentose) sugar found in RNA nucleotides
What is the structure of deoxyribose?
The 5-carbon sugar found in DNA nucleotides.
What Is the structure and definition of purine?
Adenine and Guanine – nitrogenous bases consisting of a double ring structure
What is the definition and structure of pyrimadine?
Thymine, Cytosine and Uracil – nitrogenous bases consisting of a single ring structure.
What is a polynucleotide?
A polymer consisting of many nucleotide monomers covalently bonded together, e.g. DNA or RNA.
What are the base-pairing rules?
Between nitrogenous bases in nucleic acids. A pairs with T (or U) and G pairs with C.
What is messenger RNA (mRNA)
a type of RNA polynucleotide involved in protein synthesis. Carries the information coding for a polypeptide from the nucleus to the ribosomes in the cytoplasm
What is transfer RNA (tRNA)
a type of RNA polynucleotide involved in protein synthesis. It transports amino acids to the ribosomes to be added to the growing polypeptide chain
Found in the cytoplasm
What is a gene?
A length of DNA that carries the code for the synthesis of one (or more) specific polypeptides.
How do the two polynucleotide strands in a DNA molecule run?
In opposite directions, Anti-parallel
What is semi-conservative replication?
The replication of a DNA strand where the 2 strands unzip, and a new strand is assembled onto each ‘conserved’ strand according to the complementary base-pairing rules. The replicated double helix consists of one old strand and one new strand.
What is the double helix?
Describes the structure of DNA, a twisted helix of 2 strands with bases joining the strands.
What are the 2 types of nucleic acid?
DNA –Deoxyribonucleic Acid
RNA – Ribonucleic Acid
What are the two types of nucleic acid also known as?
- macromolecules
- polymers
- polynucleotides (because they are made up of smaller subunits called nucleotides)
What are the monomers of nucleic acids?
nucleotides
What are nucleotides made up of?
- Phosphate group
- Pentose sugar - deoxyribose or ribose
- Nitrogen-containing base (organic base)
how many different nitrogen containing bases are there?
five
What groups are the nitrogen containing bases?
purine bases
pyrimidine bases
What are the purine bases?
Adenine
Guanine
What are the pyrimidine bases?
- Thymine
- Cytosine
- Uracil
What are the 4 bases in DNA?
Adenine and Thymine
Cytosine and Guanine
What are the 4 bases in RNA?
Cytosine and Guanine
Adenine and Uracil
What is the structure of DNA?
- Double stranded polynucleotide
- Nucleotides together joined by condensation reactions between the deoxyribose sugar of one nucleotide and the phosphate group of another. (sugar-phosphate backbone)
- The nitrogen-containing bases point sideways
Where is most DNA found in eukaryotic cells?
in the nucleus
How are the bases held together?
by hydrogen bonds
What are the rules between purine and pyrimidine bases?
A purine base must always be opposite a pyrimidine base
What is the complementary base pairing between Adenine…
and
Cytosine…
Adenine always pairs with Thymine
and
Cytosine always pairs with Guanine
How many bonds link cytosine and guanine?
three
How many hydrogen ions link adenine and thymine?
Two
What are the three types of RNA?
- Messenger RNA (mRNA)
- Ribosomal RNA (rRNA)
- Transfer RNA (tRNA)
What is the difference in nitrogenous base between DNA and RNA
RNA contains the nitrogenous base Uracil instead of Thymine
Is RNA double or single stranded?
single stranded
How does mRNA structure and movement occur?
- long single strand formed into
a helix - Made in the nucleus
- Passes into cytoplasm
- Moves to the ribosomes
Where is rRNA made, found and roles?
- Made in the nucleolus
- Found in the cytoplasm
- Forms ribosomes
- Ribosomes are made of rRNA & protein
What is the role, structures of tRNA?
- Forms clover-leaf shape.
- One end attaches to a specific amino acid
- The other end has a triplet of bases used in protein synthesis,
called the ANTICODON
How does DNA replication work?
- When cells divide, each new cell must receive an IDENTICAL copy of the genetic material.
- DNA must be able to copy itself exactly to form 2 new DNA molecules.
- This is called DNA replication and it takes place during INTERPHASE in the cell cycle
What is the DNA replication process?
- Two strands of DNA must unwind and split apart, hydrogen bonds break.
- Next, free complementary nucleotides line up against the DNA strands. The nucleotides are first activated by extra phosphate groups
- The enzyme DNA Polymerase joins them together forming 2 new DNA molecules
What were the three theories in the 1950s on semi-conservative replication?
- Conservative replication
- Dispersive replication
- Semi-conservative replication
What evidence did the meselsohn and stahl produce?
- that each DNA strand serves as a template for the synthesis of the new strands.
- And each of the 2 DNA molecules produced consist of a) an original strand and
b) a new strand.
What scientists caused the semi-conservative theory of replication to be accepted?
- meselsohn
- stahl
How did meselsohn and stahl use to demonstrate the DNA strands?
used the bacteria Escherichia coli (E.coli) and two Nitrogen isotopes – N14 (light) & N15 (heavy)
What did the experiment carried out by meselsohn and stahl involve?
- First the E.coli were grown on a media containing N15 (heavy isotope) for many generations.
So all the nitrogenous bases contained N15. - They then separated the DNA using centrifugation and only 1 heavy band was obtained
- E.coli was then transferred to media containing N14 (light isotope) and allowed to replicate for 1, 2 and 3 generations.
- Some of the DNA from each generation was extracted and centrifuged.
What were the results of the experiment conducted by meselsohn and stahl
How does DNA control all the cell’s activities
- Chemical reactions control the cells activities
- All chemical reactions in the cell are controlled by enzymes
- Enzymes are proteins
- The sequences of bases on the DNA make up codes for particular protein molecules
What does the shape and florin of the protein depend on
The exact sequence of Amino acids - primary structure
What does the sequence of bases in the DNA molecule control?
the exact sequence in which the amino acids join together when a protein is made on the ribosomes
What is the triplet code?
- 20 different amino acids, which each are coded by a sequence of 3 bases on the DNA molecule
- each set of three bases is called a codon
- sequence of DNA is read in a particular direction and only one of the two strands are used.
Why do you use three bases in the triplet code?
because each base can not code for 1 amino acids.
There’s 20 different AA, if there were only 2 base pairs 16 different codes are possible
if a comb of 3 bases pairs or triplet codes are used there are 64 different codes. More than enough for 20 AA
After a series of experiments using RNA, the triplet code for each AA was determined
What is the degenerate code?
discovered that there is more than one triplet code for most amino acids
What is a stop codon?
3 particular codons that did not code for amino acids at all
What is the codon AUG usually called?
the start codon
What is CUGAGCUAG read as?
CUG-AGC-UAG
(non-overlapping)
How many genes do humans have as an estimate?
14000
Where are Amino acids found?
found in the cytoplasm
What is the shape and structure of tRNA?
chain of nucleotides, in the shape of a clover leaf. Each molecule has a different triplet of bases called an anticodon (different for each AA)
What is at the other end of every tRNA molecule?
a triplet CCA, this is where the amino acid attaches. The tRNA molecule picks up its AA and moves towards the ribosomes.
What is translation process?
- The mRNA has already passed from the nucleus to the endoplasmic reticulum by moving through the nuclear pores and entering the cytoplasm
- the mRNA molecule attaches to a ribosome, the genetic code of mRNA is translated into a AA sequence
What is the second stage of the translation process (from AA sequence)
- tRNA molecules bind with the exposed bases of the mRNA.
- The ribosome holds two amino acids together as a peptide bond forms.
- This is catalysed by an enzyme.
- The ribosome moves along the mRNA, and “reads” the next codon.
- The tRNA is released and passes back to the cytoplasm to pick up another amino acid.
- The polypeptide chain continues to grow until a “stop” codon is reached.
- A new protein molecule has been formed!
What is an overall summary of protein synthesis?
- A mRNA strand is made of the gene, using ONE strand of the DNA as a template
- mRNA passes out to cytoplasm and binds to a ribosome
- The ribosome moves along the mRNA and reads the mRNA codons
- tRNA molecules bring the correct amino acids to the ribosome, through complementary binding between anticodon and mRNA codon
- The polypeptide strand is built up
Protein synthesis, how does it work?
- proteins are formed using ribosomes in the cytoplasm of a cell
- the info codes for proteins in the nucleus
- DNA is too large to move out of the nucleus to the ribosomes
- info is sent from the DNA to the cytoplasm for transcription
What is transcription?
where Information in DNA is used to build a molecule of RNA (Ribonucleic acid)
This messenger RNA (mRNA) takes a “message” from the DNA to ribosomes in the cytoplasm.
What is the difference between DNA and RNA?
- The pentose sugar in RNA is Ribose not Deoxyribose
- The nitrogen containing base Thymine is replaced with Uracil.
What is the process of Transcription?
- The DNA double helix unwinds and unzips at the start of the gene.
- Hydrogen bonds between base pairs break and the bases are exposed.
- Free activated RNA nucleotides align with the exposed DNA nucleotides. On one strand of the DNA molecule only. (template)
- RNA Polymerase links the RNA
What is the second process of transcription (after enzyme links)?
- As the single strand of mRNA forms, the DNA helix reforms behind it.
- The mRNA molecule contains triplets of bases called codons based on the DNA sequence
- The mRNA molecule is small enough to leave the nucleus through a nuclear pore in the nuclear envelope.
- Finally the mRNA attaches to a Ribosome – (often on the RER).
