DNA, Genes and Chromosomes Flashcards
What are the differences between prokaryotic and eukaryotic genetic material?
- prokaryotic DNA is found in the cytoplasm, eukaryotic DNA is found in the nucleus
- prokaryotic DNA is circular, eukaryotic DNA is linear (chromatin)
- prokaryotic DNA is not associated with proteins, eukaryotic DNA is associated with proteins (histones)
- prokaryotic DNA is smaller, eukaryotic DNA is longer
- prokaryotic DNA does not contain introns, eukaryotic DNA does
How is DNA packed into chromosomes?
Hydrogen bonds connect complementary base pairs on opposite strands of DNA, which is wound into a double helix. DNA wraps around proteins called histones to form structures called nucleosomes, which are the basic units of chromatin. Chromatin is what makes up the chromosome
What are the similarities and differences between RNA and DNA?
- Both contain a phosphate group, pentose sugar and nitrogenous base
- Both contain adenine, cytosine and guanine
- Both polymers of nucleotides joined by phosphodiester bonds
- DNA is double stranded whereas RNA is single stranded
- DNA has a thymine base whereas RNA has a uracil base
- DNA has a deoxyribose sugar whereas RNA has a ribose sugar
Where is DNA found in eukaryotic cells?
DNA is found within chromosomes in the nucleus, however can also be found in structures such as mitochondria and chloroplasts, however like prokaryotic DNA, it is short, circular and not associated with proteins
What is a gene?
A base sequence of DNA that codes for:
- the amino acid sequence of a polypeptide
- a functional RNA (including rRNA and tRNA)
What is a locus?
A fixed position that a gene occupies on a particular DNA molecule
If the DNA base sequence is TACGGTAAT, what is the mRNA base sequence?
AUGCCAUUA
complementary base pairing rules, except U (rather than A) bonds with T
If the mRNA base sequence is AUGCCAUUA, what is the tRNA anticodon?
UACGGUAAU
complementary base pairing rules, except A bonds to U, and U bonds to A
If the DNA base sequence is TACGGTAAT, what is the tRNA anticodon?
UACGGUAAU
the bases will stay the same, except for T which is replaced with U
Which base sequence codes for the amino acid sequence?
mRNA
What 3 words are used to describe the genetic code?
universal, non-overlapping and degenerate
What does non-overlapping mean?
Each base is only used once in coding for an amino acid
What does universal mean?
The genetic code is identical in all organisms
What does degenerate mean?
More than one codon codes for a single amino acid
What is a codon?
3 adjacent bases on mRNA that code for an amino acid
Why are 3 bases needed to code for each amino acid?
Because at least 20 different codons are needed to code for 20 different amino acids
1 base = 4^1, 4 triplets
2 bases = 4^2, 16 triplets
3 bases = 4^3, 64 triplets - 64>20
What is the advantage of a cell having a degenerate code?
It is less likely that a change to the DNA will change the amino acid sequence (silent mutation)
What is a sequence of 3 bases called?
triplet
Why does much of the nuclear DNA in eukaryotes not code for polypeptides?
- there are non-coding multiple repeats of base sequence between genes
- only some sequences (exons) code for amino acid sequences
- within genes, exons are separated by one or more non-coding sequences called introns
What 2 molecules are found within the nucleus?
- DNA
- histones
Describe how a gene is a code for the production of a polypeptide
A gene is a base sequence on DNA. The base sequence in the triplet code determines the sequence of amino acids in the production of polypeptides
Define exon
Base sequence in DNA that codes for a polypeptide
Describe how phosphodiester bonds form between 2 nucleotides
- form in a condensation reaction which releases a molecule of water
- between deoxyribose and phosphate
- catalysed by DNA polymerase
Where are non-coding regions positioned in the genome
between genes
What is a homologous pair of chromosomes?
2 chromosomes carrying the same genes
