Unit 4 DNA, RNA & Protein synthesis Flashcards
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Describe the similarities and differences in DNA in prokaryotic cells and eukaryotic cells.
- Both Eukaryotes and prokaryotes DNA are made of DNA nucleotides containing deoxyribose, a phosphate group, and a nitrogenous base
- Joined by phosphodiester bonds
PROKARYOTES - DNA is shorter
- DNA is circular
- DNA is not associated with proteins
EUKARYOTES - DNA is longer
- DNA is linear
- DNA associated with histones - to form chromosomes
Describe the DNA in chloroplasts and mitochondria of eukaryotic cells.
Like prokaryotes=
- DNA is short
- DNA is circular
- DNA is not associated with proteins
Describe what a gene codes for.
AND definition of a locus
A gene is a base sequence of DNA that codes for
- Amino acid of a polypeptide
- Functional RNA
Locus - A gene occupies a particular fixed position on a chromosome
Describe the features of genetic code & a sequence of 3 bases.
- A sequence of 3 DNA bases(a triplet) codes for a specific amino acid Genetic code has 3 features - Degenerate - Universal - Non-overlapping
Describe what is meant by degenerate and universal.
OPTIONAL
Degenerate - Each amino acid is coded for by more than one triplet of bases
Universal - Same triplet of bases code for the same amino acid in all organisms
Describe what is meant by an intron and an exon
IN EUKARYOTIC most of DNA made up of introns
Introns (Non-coding repeats) =
- Sections of DNA that do not code for amino acids
, found in eukaryotic DNA but not prokaryotic DNA
Exons =
- Base sequences of DNA that do code for amino acids
Describe the definition of the genome and proteome
Genome
- An organisms complete set of genes in a cell
- Usually doesn’t change
Proteome
- Full range of different proteins the cell is able to produce
- Constantly changing
Describe the strcuture of mRNA
- Short single-stranded molecules found in the nucleus and cytoplasm
- Made in transcription = copied from DNA therefore complementary to DNA sequence
- Longer than tRNA
Describe the structure of tRNA
- tRNA found in cyptoplasm
tRNA involved in translation, cloverleaf shape - On one side is an anticodon(↓) = complementary to codons on mRNA
- Opposite side is amino acid binding site which is specific
Describe the difference between transcription in eukaryotes and prokaryotes.
- In prokaryotes transcription directly creates mRNA as prokaryotic DNA doesn’t contain introns
- In Prokaryotes transcription takes place in the cytoplasm but in eukaryotes, it occurs in the nucleus
Describe the process of transcription.
Transcription - production of mRNA from DNA
- Hydrogen bonds between DNA bases break;
- DNA uncoiled but only one DNA strand acts as a template
- Free RNA nucleotides in nucleus align opposite to complementary bases
- Complementary base pairs formed A-T C-G G-C
Uracil replaced with Thymine in RNA A-U - RNA polymerase joins adjacent RNA nucleotides by phosphodiester bonds
- forms Pre-mRNA which is spliced to form mRNA to remove introns
- Leaves nucleus through nuclear envelop pores
Describe where translation takes place in eukaryotes and prokaryotes.
Cytoplasm of ribosomes
Outline ribosomal RNA
Describe the process of translation in eukaryotes
Translation - production of polypeptide chain(protein)
- mRNA attaches to the ribosome in the cytoplasm and ribosome moves to find the start codon
- tRNA brings specific amino acids to ribosome and anticodons on tRNA bind to complementary mRNA codons
- Amino acids join by peptide bonds with the use of ATP and is catalysed by ribosome
- Empty tRNA released after amino acids joined to the polypeptide
- Ribosome moves along mRNA to form polypeptide, stops at end codon as doesn’t code for amino acid, so ribosome detaches and translation complete
