A-level Biology - 3.1.7 DNA, Genes and Chromosomes Part 2
This deck covers key concepts in DNA structure, replication, and genetic coding, focusing on differences between eukaryotic and prokaryotic DNA, gene expression, and chromosome structure.
Describe stage 3 of semi-conservative replication
Condensation reactions join nucleotides - catalysed by enzyme DNA polymerase H bonds form between bases (on original and new strands)

Key Terms
Describe stage 3 of semi-conservative replication
Condensation reactions join nucleotides - catalysed by enzyme DNA polymerase H bonds form between bases (on original and new strands)
Describe stage 4 of semi-conservative replication
Each new DNA molecule contains one strand from original DNA molecule and one new strand (Double strand twists again)
DNA molecules and histone are coiled up very tightly to make _ ________
compact chromosomes
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| Term | Definition |
|---|---|
Describe stage 3 of semi-conservative replication | Condensation reactions join nucleotides - catalysed by enzyme DNA polymerase H bonds form between bases (on original and new strands) |
Describe stage 4 of semi-conservative replication | Each new DNA molecule contains one strand from original DNA molecule and one new strand (Double strand twists again) |
Eukaryotic DNA is & _ with ______ | Nuclear Eukaryotic DNA is Linear & Associated with Proteins |
What is a DNA molecule in eukaryotic cells wound around? | (Proteins called) histones |
What do histone proteins do? | Help support the DNA |
DNA molecules and histone are coiled up very tightly to make _ ________ | compact chromosomes |
___________ and ___ in eukaryotes have their own DNA | Mitochondria and chloroplast |
What is the DNA in mitochondria and chloroplast (in eukaryotes) like? | Similar to prokaryotic DNA ∵ its circular and shorter than DNA in nucleus & it's not associated with histone proteins |
What is DNA like in prokaryotic cells? | DNA molecules are shorter and circular & isn't wound around histones |
How does prokaryotic DNA fit into cells? | Condenses to fit in cell by supercoiling |
What is a gene? | Sequence of DNA bases that codes for either a polypeptide or functional RNA |
What do different polypeptides have? | They have different no. and order of amino acids |
What determines the order of amino acids in a polypeptide? | The order of bases in a gene |
What is each amino acid coded by? | A sequence of 3 bases in gene = called triplet |
What is functional RNA? | RNA molecules other than mRNA (e.g. tRNA & rRNA) |
What is meant by a cell's genome? | The complete set of genes in the cell |
What is meant by a cell's proteome? | Full range of proteins that the cell is able to produce |
Most DNA in eukaryotic cells _ code for polypeptides | DON'T |
In eukaryotic DNA, genes that code for _ contain sections that… | In eukaryotic DNA, genes that code for polypeptides contain sections that don't code for amino acids |
What are introns? | Sections of DNA that don't code for amino acids |
Can there be several introns within a gene? | Yes |
What are exons? | Bits of gene that do code for amino acids |
When are introns are removed? | During protein synthesis |
Prokaryotic DNA doesn't have ____ | introns |
Eukaryotic DNA contains regions of _ _____ ____ of genes | Eukaryotic DNA contains regions of multiple repeats outside of genes |
What are multiple repeats? | DNA sequences that repeated over and over again e.g. CCTTCCTTCCTT |
Multiple repeats ____ code for amino acids & are called ______ ____ | Multiple repeats don't code for amino acids & are called non-coding repeats |
What is order of bases like in alleles and what does this lead to? | Order of bases in each alleles is slightly different ∴ they code for slightly different versions of the same polypeptide |
What is homologous pair? | Pair of matching chromosomes: both chromosomes are same size & have same genes (BUT could have different alleles) |
Where are alleles coding for the same characteristic found on chromsomes in a homologous pair? | Found at same fixed position (locus) on each chromosome in a homologous pair |
Explain why DNA helicase is important in DNA replication (2) | Breaks H-bonds (So) nucleotides can attach/strands can act as templates |
Draw 2 nucleotides joining together |