Chapter 8: DNA, Genes and Protein Synthesis Flashcards
What is a gene?
A section of DNA that contains the coded information for making polypeptides and functional RNA.
In what form is the coded information?
A specific sequence of bases along the DNA molecule.
What is a locus?
The particular position on a DNA molecule where the gene is located.
What does a gene code for?
- The amino acid sequence of a polypeptide.
- Or a functional RNA, including ribosomal RNA and transfer RNAs.
Why is the genetic code considered degenerate?
Most amino acids are coded for by more than one triplet.
Why is the genetic code considered non-overlapping?
Each base is read only once.
Why is the genetic code considered universal?
With a few minor exceptions, each triplet codes for the same amino acid in all organisms. (indirect evidence for evolution)
What are exons?
Coding sequences- required (EXit the nucleus)
What are introns?
Non-coding sequences- removed (stay IN the nucleus)
What is a chromosome?
A thread-like structure in which DNA is tightly packaged within the nucleus.
What is a centromere?
A specialised DNA sequence of a chromosome that links a pair of sister chromatids.
What is a chromatid?
One thread of a chromosome.
How is DNA packed into a chromosome?
1: DNA molecule is combined with histones.
2: DNA-histone complex is coiled.
3: Coils fold to form loops.
4: Loops coil and pack together to form the chromosome.
What is a cell that has paired chromosomes (one from each parent) called?
Diploid
What are two chromosomes that carry the same genes called?
Homologous pairs
Which type of cell division produces four daughter cells, each with half the number of chromosomes as the parent cell?
Meiosis
What is one type of alternative form of a gene called?
Allele
What ‘change’ in the base sequence of a gene produces new allele of that gene?
Mutation
What is an enzyme with a new shape that may not fit its substrate called?
Non-functional enzyme
What is a codon?
The sequence of three bases on mRNA that codes for a single amino acid.
What is a genome?
The complete set of genetic material in an organism.
What is a proteome?
The full range of proteins produced by the genome.
What is RNA?
Ribonucleic acid
A polymer made up of repeating mononucleotide sun-units. It forms a single strand of: the pentose sugar ribose, one of the organic bases adenine, guanine, cytosine and uracil, and a phosphate group.
What type of strand is a DNA, mRNA and tRNA molecule?
DNA: double
mRNA: single
tRNA: single
What is the order of increasing size of DNA, mRNA and tRNA?
tRNA- smaller
mRNA: variable
DNA: largest
What type of shape is a DNA, mRNA and tRNA molecule?
DNA: double helix
mRNA: single helix
tRNA: clover shape
What type of sugar is present in a DNA, mRNA and tRNA molecule?
DNA: deoxyribose
mRNA: ribose
tRNA: ribose
What are the different bases in a DNA, mRNA and tRNA molecule?
DNA: A, T, C, G
mRNA: A, U, C, G
tRNA: A, U, C, G
What is the quantity of DNA, mRNA and tRNA molecules in cells?
DNA: constant (gametes)
mRNA: varies
tRNA: varies
What is the stability of DNA, mRNA and tRNA molecules like?
DNA: very stable
mRNA: unstable
tRNA: more stable than mRNA but less stable than DNA.
What is an anticodon?
Three bases at the opposite end of the tRNA.
What does the anticodon pair with?
The complementary codon on the mRNA.
What are the stages of protein synthesis?
1: Transcription of the gene in the nucleus- an mRNA strand is formed.
2: Processing of the mRNA
3: Translation of the mRNA in a ribosome- a polypeptide chain is formed.
4: Modification of the protein
What is the process of transcription?
(condensation reaction)
1: DNA helicase unwinds the double helix of DNA by breaking the hydrogen bonds between the base pairs.
2: The two strands of DNA are separated so free RNA nucleotides can fit in.
3: Free RNA nucleotide bases bind to the template DNA by their complementary base pair rules.
4: RNA polymerase joins the ribose phosphate backbone of the RNA nucleotides to form a molecule of pre-mRNA.
5: The single pre-mRNA strand moves away from the DNA helix and RNA polymerase zips the two strands of DNA back together.
6: The pre-mRNA strand is processed through splicing to form mRNA that is ready for translation.
What is splicing?
The base sequences corresponding to the introns are removed and the functional exons are joined together.
What is the process of translation?
1: A ribosome attaches to the mRNA at an initiation codon.
2: The bond between the amino acid and the tRNA is cut and a peptide bond is formed between the two amino acids. This operation is catalysed by ribozyme.
3: The polypeptide chain elongates one amino acid at a time, and peels away from the ribosome, folding up into a protein as it goes. This continues for hundreds of amino acids until a stop codon is reached, when the ribosome falls apart, releasing the finished protein.
4: The next amino acid-tRNA attaches to the adjacent mRNA codon. The anticodon on the tRNA binds to the codon on the mRNA.
5: The ribosome moves along one codon so that a new amino acid-tRNA can attach. The free tRNA molecule leaves to collect another amino acid. The cycle repeats from step 3.
