Chapter 6: Nucleic Acids And Protein Synthesis Flashcards
What are nucleotides made up of?
- A nitrogen containing base
- A pentose sugar
- A phosphate group
What are the four nitrogen containing bases found in DNA?
Adenine, guanine, thymine, cytosine
What are the four nitrogen containing bases found in RNA?
Adenine, guanine, uracil, cytosine.
What can the pentose sugar be in DNA and RNA?
DNA-deoxyribose
RNA- ribose
Where does the linking of nucleotides take place and when?
This takes place in the nucleus, during the interphase of the cell cycle.
What are the purine bases?
Adenine and guanine
What are the pyrimidines?
Cytosine and Thymine
What are the complementary base pairs?
A with T and C with G
Describe the structure of a polynucleotide.
Each polynucleotide strand contains covalent sugar-phosphate bonds linking the 5-carbon of one sugar molecule and the 3-carbon of the next. The polynucleotide strand is said to have 3’ and 5’ ends.
Describe the structure of DNA.
DNA is made up of two antiparallel polynucleotide strands lying side by side, held together by hydrogen bonds. These strands are arranged into a double helix structure. The way the two strands line up is very precise.
What is the process of semi-conservative DNA replication?
It occurs during S phase of interphase.
- The DNA double helix unwinds and ‘unzips’ as the hydrogen bonds between the bases break by helicase.
- In the nucleus, there are nucleotides to which two extra phosphates have been added to activate the nucleotides.
- Each of the bases pairs up with its complementary base on each of the old DNA strands. The enzyme DNA polymerase links the nucleotides to each other by catalysing phosphodiester bonds. The two extra phosphates are broken off and released into the nucleus.
What is a gene?
A part of a DNA molecule where the nucleotide sequence codes for just one polypeptide, is called a gene.
What is a mutation with reference to nucleotides?
A change in the nucleotide sequence of a gene, which may then result in an altered polypeptide is called a mutation.
What is a triplet code?
It is a sequence of three bases standing for one amino acid.
What causes sickle cell anaemia?
The gene which codes for one of the amino acid sequence in the B-globin polypeptide chain in haemoglobin is substituted with the Hbs(sickle cell) allele of the gene, as opposed to the Hba (normal allele). This causes the outer surface of haemoglobin to become less soluble due to the substitution being a non-polar amino acid.
How does DNA affect the primary structure of a protein?
DNA codes for multiple proteins and controls the exact order in which amino acids join together when proteins are made.
How does DNA control the activities of a cell?
All chemical reactions are controlled by enzymes. Enzymes are proteins. Genes code for proteins, controlling which proteins are made. Thus, DNA controls the cell’s activities.
When does transcription of a gene begin? ref. promoter
Transcription of a gene begins when RNA polymerase binds to a control region of the DNA called a promoter and ends when the enzyme reached a terminator sequence.
Describe the transcription process of protein synthesis.
In the nucleus, the DNA strands unwind and ‘unzip’ as the hydrogen bonds between them break. Free activated RNA nucleotides pair up with the exposed bases of one strand only. As the RNA nucleotides pair up with their complementary ones, their sugar-phosphate groups are bonded together by RNA polymerase. The transcription begins when RNA polymerase binds to a control region of the DNA known as a promoter and ends when the enzyme has reached a terminator sequence. The hydrogen bonds holding DNA and RNA together are broken and the double stranded DNA reforms. The new single stranded molecule formed is known as mRNA. It leaves the nucleus through a nuclear envelope.
Describe the translation process of protein synthesis.
In the cytoplasm, there are free amino acids and transfer RNA (tRNA) molecules. At one end of a tRNA molecule is a site to which an amino acid can bind. At the other end are three unpaired bases. This base triplet is called an anticodon. Each tRNA molecule bonds with a particular amino acid. Meanwhile, also in the cytoplasm, the mRNA molecule binds to the small subunit of the ribosome. The ribsome is made up of RNA and protein. A tRNA molecule enters the large subunit of the ribosome and attaches to the mRNA. The first three exposed bases or CODON are always AUG with the complementary anticodon UAC on the tRNA. This tRNA molecule has the amino acid methionine attached to it. The anticodon on the tRNA and the codon on the mRNA form hydrogen bonds. Only two tRNA molecules can fit in the large subunit of the ribosome at the same time. A second tRNA molecule bonds with the next three bases bringing a different amino acid. The two amino acids are held closely together and a peptide bond is formed between them catalysed by the enzyme peptidyl transferase which is found in the small subunit of the ribosome. The ribosome moves along the mRNA , reading the next codon and bringing a third amino acid which bonds with the second one. The first tRNA leaves and is reused. The polypeptide chain continues to grow until a ‘stop’ codon is exposed on the ribosome. This is UAA, UAC or UGA.
