The Molecular Basis of Life

Question 1

describe the nucleus

Answer 1

-largest organelle in animal cells
-contains majority of genetic material
-contains DNA and protein assembled into chromatin

Question 2

describe the structure of the nucleus

Answer 2

-separated from rest of cell by nuclear envelope
-envelope has nuclear pores
-contiguous with ER
-contains nucleolus where ribosomes are assembled

Question 3

what enters and leaves nucleus?

Answer 3

-RNA and ribosomes leave nucleus
-proteins enter nucleus
-nuclear pores regulate what comes in and out and this needs ATP

Question 4

function of nucleus

Answer 4

Storing genetic material - DNA
Replicating DNA
Transcribing RNA

Question 5

describe DNA

Answer 5

-stores cell’s genetic information
-helical structure
-very stable
-very long

Question 6

describe the structure of DNA

Answer 6

-made of nucleotide monomers
-adenine, cytosine, thymine and guanine bases
-nucleotides form linear strings w phosphate backbone
-two anti-parallel chains which form double helix

Question 7

describe DNA packaging

Answer 7

-DNA wraps around histones to form nucleosome
-string of nucleosomes form coils called solenoids

Question 8

describe chromatin and chromosomes

Answer 8

-Nucleosomes coiled into solenoids form chromatin
-chromatin is organised into chromosomes
-chromosomes are only visible when condensed in metaphase
-Chromosome is 10000-fold shorter than the DNA it contains
-their structure is maintained by protein scaffolding

Question 9

what do metaphase chromosomes look like?

Answer 9

-consist of two sister chromatids joined at the centromere
-Structure maintained by protein scaffold

Question 10

what is the human genome?

Answer 10

total genetic content distributed in 22 pairs of chromosomes and the 2 sex chromosomes
-Genes are arranged linearly along the chromosome

Question 11

what are genes?

Answer 11

fundamental units of heredity

Question 12

describe genes

Answer 12

-present at particular loci on chromosomes
-alternate versions (alleles) on the gene present at same locus on homologous chromosomes
-each diploid cell contains two alleles of each gene
-homozygous means alleles are same
-heterozygous means alleles are different

Question 13

describe DNA replication - eukaryotes

Answer 13

Occurs during S phase of cell cycle
Is semi-conservative
-DNA helicase unwinds the double helix
-leading strand is synthesised continuously in the 5’-3’ direction by DNA polymerase
-lagging strand is synthesised discontinuously to form ozakazi fragments which are then joined by DNA ligase

Question 14

why are DNA polymerases said to be proof-reading?

Answer 14

because they can correct errors

Question 15

what are the three major forms of RNA?

Answer 15

• rRNA (ribosomal)
• tRNA (transfer)
• mRNA (messenger)

Question 16

how is RNA different to DNA?

Answer 16

-single stranded
-sugar is ribose
-uracil replaces thymine

Question 17

describe transcription

Answer 17

Synthesis of RNA from a DNA template
-carried out by RNA polymerase
-promoter region directs RNA polymerase
-consists of initiation, elongation and termination
-primary transcription contains introns which are removed by splicing
-goes through modifications e.g. 5’ cap and poly-A tail
-mature mRNA contains only exons which dictate sequence of amino acids in protein

Question 18

what is non-coding RNA?

Answer 18

functional RNA molecule that is not translated into proteins

Question 19

what are examples of ncRNA?

Answer 19

-miRNA (microRna, small non-coding RNA)
-siRNA (small interfering RNA)
-piRNA (piwi-interacting RNA)
-IncRNA (long non-coding RNA)

Question 20

describe oral cancer

Answer 20

-6th most common cancer in UK
-survival rates not improving w treatment
-associated w mutations of genes e.g p53 which cause cells to divide abnormally and form tumour
-genetic abnormalities can be used to determine treatment