3.4.1 - DNA, genes and chromosomes

Question 1

how is DNA stored in eukaryotic cells?

Answer 1

eukaryotic cells have linear DNA molecules that exist as chromosomes

Question 2

describe chromosomes

Answer 2

thread-like structures, each made up of 1 long molecule of DNA and its associated proteins

Question 3

where are chromosomes found in eukaryotic cells

Answer 3

chromosomes are found in the nucleus

Question 4

in eukaryotic cells, what are DNA molecules wound around

Answer 4

the DNA molecule is really long so has to be wound up so it can fit in the nucleus, it’s wound around proteins called histones

Question 5

in eukaryotic cells what do histone proteins help do

Answer 5

histone proteins help to support the DNA, the DNA (and protein) is then coiled up very tightly to make a compact chromosome

Question 6

what organelles in eukaryotic cells also have DNA?

Answer 6

mitochondria and chloroplasts also have their own DNA

Question 7

what is the DNA in mitochondria and chloroplasts like?

Answer 7

similar to prokaryotic DNA as it’s circular/shorter than DNA molecules in the nucleus and isn’t associated with histone proteins

Question 8

what do prokaryotes carry DNA as?

Answer 8

prokaryotes carry DNA as chromosomes

Question 9

what is different about the DNA in prokaryotes compared to eukaryotes

Answer 9

the DNA molecules are shorter and circular, the DNA isn’t wound around any histones and condenses to fit in the cell by supercoiling

Question 10

what does DNA contain?

Answer 10

genes

Question 11

what is a gene

Answer 11

a gene is a base sequence of DNA that code for the amino acid sequence of a polypeptide or a functional RNA (including ribosomal RNA and tRNAs)

Question 12

what differs different polypeptides

Answer 12

different polypeptides have a different number and order of amino acids

Question 13

what determines the order of amino acids in a polypeptide

Answer 13

the order of bases in a gene determines the order of amino acids in a particular polypeptide

Question 14

what is each amino acid coded for by?

Answer 14

each amino acid is coded for by a sequence of 3 bases in a gene called a triplet or a codon

Question 15

what happens to make a polypeptide

Answer 15

to make a polypeptide, DNA is 1st copied into mRNA which s the 1st stage of protein synthesis

Question 16

what is functional RNA

Answer 16

functional RNA is RNA molecules other than mRNA, which perform special tasks during protein synthesis e.g. tRNA and ribosomal RNA (rRNA)

Question 17

in eukaryotes does all nuclear DNA code for polypeptides?

Answer 17

in eukaryotes, lots of the nuclear DNA doesn’t code for polypeptides

nuclear DNA = DNA stored in the nucleus

Question 18

what are introns

Answer 18

genes that do code for polypeptides contain sections that don’t code for amino acids, these sections of DNA are called introns

Question 19

what are intron’s purpose

Answer 19

there can be several introns within a gene and their purpose isn’t known for sure

Question 20

what happens to introns in eukaryotic cells during protein synthesis

Answer 20

introns in eukaryotes are removed during protein synthesis so they don’t affect the amino acid order

Question 21

do prokaryotic cells have introns

Answer 21

prokaryotic DNA don’t have introns

Question 22

what are exons

Answer 22

all of the bits of a gene that do code for amino acids are called exons

Question 23

what does eukaryotic DNA also contain?

Answer 23

eukaryotic DNA also contains regions of multiple repeats outside of genes . these are DNA sequences that repeat over and over. these areas don’t code for amino acids and are called non coding multiple repeats

Question 24

what are alleles

Answer 24

a gene can exist in more than one form, these forms are called alleles

Question 25

order of bases in alleles and what they code for

Answer 25

the order of bases in each allele is slightly different, so they code for slightly different versions of the same polypeptide

Question 26

how many pairs of chromosomes do humans have

Answer 26

23 pairs of chromosomes, so 46 in total

Question 27

what are homologous pairs

Answer 27

pairs of each matching chromosomes are called homologous pairs

Question 28

similarities/differences in homologous pairs

Answer 28

in a homologous pair both chromosomes are the same size and have the same genes, although they could have different alleles

Question 29

where will alleles coding for the same characteristic be found?

Answer 29

alleles coding for the same characteristic will be found a the same fixed position (locus) on each chromosome in a homologous pair