2.3 Genes, DNA, RNA Flashcards
What is a nucleotide?
Building blocks of nucleic acids = a nitrogenous base; a sugar; one or more phosphates
Name the types of nitrogenous base are there and how they are grouped?
Purines:
Adenine
Guanine
Pyrimidines:
Cytosine
Thymine
Uracil
What are the 2 types of sugar?
Deoxyribose & Ribose
What is DNA?
Deoxyribonucelic acid
a double stranded helix of 4 deoxyribonucleotides (A, T, C & G) linked together through phosphodiester bonds
What is RNA?
single stranded chains of 4 deoxyribonuleotides (A, U, C & G)
What is the tertiary structure of RNA?
It forms a ‘clover leaf’
What is Pre-mRNA or heteronuclear RNA (hnRNA)?
the primary transcripts produced from DNA during transcription - processed and shortened to produce mature mRNA
What is Messenger RNA (mRNA)?
represents the mature RNA transcripts of the gene as a template during translation
What is Transfer RNA (tRNA)?
specific adaptors during translation
at least 20 forms that are specific for each amino acid
What is Ribosomal RNA (rRNA)?
large structural or enzymatic (ribozymes) RNA molecules that determine the structure and function of the ribosome - act as a framework for ribosomal protein binding
What is Small nuclear RNA (snRNA)?
found in large quantities in the nucleus
many are ribozymes
involved in RNA processing
What is Small interfering RNA (siRNA)?
short double stranded RNA molecules which act to suppress gene expression
What is the usual start codon in a mammalian gene?
AUG (ATG) which codes for methionine
What are the stop codons of a mammalian gene?
UAA, UAG or UGA - these do not encode any amino acid but signal to stop translation
How is a nuclosome formed?
DNA is wrapped around nucleosomes through linker DNA - a repeating series of nucleosomes and their connections are referred to as ‘beads on a string’
What is a nuclosome?
The fundamental unit of Chromatin - a complex of DNA & proteins that forms chromosomes
What is a histone octamer?
the eight protein complex found at there centre of a nucleosome - assembles when a tetramer containing 2 copies of both H3 and H4 joins with a 2 H2A/H2B dimers
What are promotors?
regions of DNA upstream of the gene that can activate gene expression and RNA polymerase II binding when activates by transcription factors
What are enhancers?
regions of DNA remote from the gene that enhance the efficiency of gene expression - the remote regions are placed in physical proximity to the gene by various activators and co-activators
What are exons?
regions that determine mRNA sequence which encode the protein
What are introns?
non-coding regions interspersed between the exons
What does a spliceosome do?
During transcription the RNA copy that is made (primary transcript) contains both interons and axons = pre-mRNA
The spliceosome splices the primary transcript to eliminate introns = mRNA
This occurs within the nucleus
